Browsing by Author "Simuyandi, Michelo"

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A pilot study on use of live attenuated rotavirus vaccine (Rotarix™) as an infection challenge model.
(2020-Oct-27) Chilengi, Roma; Simuyandi, Michelo; Chibuye, Mwelwa; Chirwa, Masuzyo; Sukwa, Nsofwa; Laban, Natasha; Chisenga, Caroline; Silwamba, Suwilanji; Grassly, Nicholas; Bosomprah, Samuel
BACKGROUND: Rotavirus remains the commonest cause of dehydrating diarrhoea, particularly in developing countries. Human infection challenge studies in children in these countries offers an opportunity to rapidly evaluate new vaccine candidates that may have improved efficacy. We evaluated use of Rotarix™ as a live-attenuated challenge agent. METHODS: We undertook an open label, exploratory study in infants receiving two standard doses of Rotarix™ at 6 and 10 weeks of age in a cohort of 22 Zambian infants. The first vaccine dose was considered as primary vaccination, and the second at day 28 as a live-attenuated virus challenge. Saliva, stool and serum samples were collected on days 0, 3, 5, 7, 14, and 28 following each dose. The primary outcome was stool shedding of rotavirus, determined by NSP2 qPCR. We calculated mean shedding index as average of natural logarithm of viral copies per gram of stool. FINDINGS: After the first dose, viral shedding was high at day 3, peaked by day 5. After the second dose, viral shedding at day 3 was low and reduced gradually in most infants until day 14. Mean shedding index was significantly lower post dose 2 across all infants and timepoints (5.0 virus copies/g of stool [95%CI: 0.3-9.7] vs 10.4 virus copies/g of stool [95%CI: 6.2-14.6]; p-value < 0.0001; rho = 0.20, SD = 4.97. Seroconversion at day 28 was associated with a mean reduction of -1.03 (95%CI = -8.07, 6.01) in viral shedding after challenge dose but this was not statistically significant (p = 0.774). A borderline positive correlation between fold-change in IgA titre at day 28 from day 0 in saliva and serum was observed; Spearman's correlation coefficient, r = 0.69; p = 0.086. INTERPRETATION: Shedding after the 'challenge' dose was reduced compared with the first dose, consistent with the induction of mucosal immunity by the first dose. This supports the use of Rotarix vaccine as a live-attenuated infection challenge. FUNDING: Medical Research Council (UK) through the HIC-Vac Network.
Association of Maternal Immunity with Rotavirus Vaccine Immunogenicity in Zambian Infants.
(2016) Chilengi, Roma; Simuyandi, Michelo; Beach, Lauren; Mwila, Katayi; Becker-Dreps, Sylvia ; Emperador, Devy M.; Velasquez, Daniel E.; Bosomprah, Samuel; Jiang, Baoming
INTRODUCTION: Live attenuated oral vaccines against rotavirus (RV) have been shown to be less efficacious in children from developing countries. Reasons for this disparity are not fully understood. We assessed the role of maternal factors including breast milk RV-specific IgA, transplacentally acquired infant serum RV-specific IgG and maternal HIV status in seroconversion among Zambian infants routinely immunized with Rotarix™ (RV1). METHODS: 420 mother-child pairs were recruited at infant age 6-12 weeks in Lusaka. Clinical information and samples were collected at baseline and at one month following the second dose of RV1. Determination of breast milk RV-specific IgA and serum RV-specific IgA and IgG was done using standardized ELISA. Seroconversion was defined as a ≥ 4 fold rise in serum IgA titre from baseline to one-month post RV1 dose 2, while seropositivity of IgA was defined as serum titre ≥ 40 and antibody variables were modelled on log-base 2. Logistic regression was used to identify predictors of the odds of seroconversion. RESULTS: Baseline infant seropositivity was 25.5% (91/357). The seroconversion frequency was 60.2% (130/216). Infants who were IgA seropositive at baseline were less likely to seroconvert compared to their seronegative counterparts (P = 0.04). There was no evidence of an association between maternal HIV status and seroconversion (P = 0.25). Higher titres of breast milk rotavirus-specific IgA were associated with a lower frequency of seroconverson (Nonparametric test for trend Z = -2.84; P<0.01): a two-fold increase in breast milk RV-specific IgA titres was associated with a 22% lower odds of seroconversion (OR = 0.80; 95% CI = 0.68-0.94; P = 0.01). There was seasonal variation in baseline breast milk rotavirus-specific IgA titres, with significantly higher GMTs during the cold dry months (P = 0.01). CONCLUSION: Low immunogenicity of RV1 vaccine could be explained in part by exposure to high antibody titres in breast milk and early exposure to wild-type rotavirus infections. Potential interference of anti-RV specific IgA in breast milk and pre-vaccination serum RV specific-IgA and IgG titres with RV1 seroconversion and effectiveness requires further research.
Clinical presentation of congenital syphilis in a rotavirus vaccine cohort study in Lusaka: a case series.
(2021-Apr-01) Sukwa, Nsofwa; Simuyandi, Michelo; Chirwa, Masuzyo; Kumwimba, Yvonne M.; Chilyabanyama, Obvious N.; Laban, Natasha ; Koyuncu, Aybüke; Chilengi, Roma
BACKGROUND: Despite an otherwise robust national antenatal clinic program, maternal and congenital syphilis remains an important public health issue in Zambia. This case series reports the clinical presentation of seven infants diagnosed with congenital syphilis in Lusaka, Zambia. CASE PRESENTATIONS: The cases in this series were incidental findings from a cohort of infants enrolled in a rotavirus vaccine immunogenicity study recruiting infants at 6 weeks of age. As part of clinical care for enrolled participants, we screened mothers of children who presented with adverse events of (i) repeated upper respiratory tract infections/coryza, (ii) skin lesions, and (iii) poor weight gain, for syphilis using rapid plasma reagin test. From a cohort of 214 mother-infant pairs enrolled between September and December 2018, a total of 115 (44.4%) of the mothers reported to have not been screened during antenatal care. Of these, four (3.5%) reported to have tested positive; and only two received treatment. Seven out of 57 (26.6%) children meeting the screening criteria had a positive rapid plasma reagin test result. The mean age at diagnosis was 4.5 months (1.3 months standard deviation), and the common presenting features included coryza (6/7), skin lesions (4/7), conjunctivitis (3/7), pallor/anemia (5/7), wasting (2/7), and underweight (5/7). Three of the seven infants were exposed to human immunodeficiency virus. Following diagnosis, all seven cases received standard treatment according to national treatment guidelines. That is, 6/7 cases received inpatient care with benzylpenicillin for 10 days, while 1/7 was treated as an outpatient and received daily procaine penicillin for 10 days. CONCLUSION: These findings suggest that, though screening for syphilis is part of the standard antenatal care in Zambia, it is not offered optimally. There is urgent need to address programmatic shortcomings in syphilis screening and treatment to avoid long-term sequelae. Additionally, clinicians need to raise their index of suspicion and rule out syphilis when confronted with these clinical symptoms, regardless of the mother's human immunodeficiency virus status.
Contribution of Maternal Immunity to Decreased Rotavirus Vaccine Performance in Low- and Middle-Income Countries.
(2017-Jan) Mwila, Katayi; Chilengi, Roma; Simuyandi, Michelo; Permar, Sallie R.; Becker-Dreps, Sylvia
The role of maternal immunity, received by infants either transplacentally or orally from breast milk, in rotavirus vaccine (RV) performance is evaluated here. Breastfeeding withholding has no effect on vaccine responses, but higher levels of transplacental rotavirus-specific IgG antibody contribute to reduced vaccine seroconversion. The gaps in knowledge on the factors associated with low RV efficacy in low- and middle-income countries (LMIC) remain, and further research is needed to shed more light on these issues.
Early linear growth retardation: results of a prospective study of Zambian infants.
(2019-Jan-14) Chilengi, Roma; Asombang, Mah; Kadota, Jillian L.; Chilyabanyama, Obvious N.; Mwila-Kazimbaya, Katayi; Ng'ombe, Harriet; Simuyandi, Michelo; Bosomprah, Samuel
BACKGROUND: Linear growth retardation is the most dominant nutritional problem globally. We aimed to describe linear growth trajectory among infants under 2 years of age using the WHO growth velocity standards. METHOD: This was a prospective cohort study of infants enrolled at 6 weeks of age and followed up for up to 24 months in Kamwala Urban Health Centre, Lusaka, Zambia. The study was conducted between April 2013 and March 2015. Infants were enrolled if they were 6-12 weeks of age and the mother was willing to participate voluntarily and provided informed consent. Anthropometric data were collected at scheduled clinic visits at 1 month, 2 months, 3 months, then quarterly until the infant was 24 months old. We defined linear growth velocity as the rate of change in height. We estimated linear growth velocity as the first derivative of the penalized cubic spline mixed effects model. RESULTS: A total of 338 children were included in the analysis. Of these, 185 (54.7%) were female, 115 (34.1%) were born to HIV positive mothers and thus classified as HIV Exposed (HE). The mean age of children at enrollment was 1.6 months (SD = 0.15). On average, the growth velocity for 3-month length increments conditional on age were 0-3 months = 2.97 cm/3mo (95%CI = 2.69, 3.25); 3-6 months = 2.62 cm/3mo (95%CI = 2.38, 2.87); 6-9 months = 1.57 cm/3mo (95%CI = 1.43, 1.71); 9-12 months = 1.18 cm/3mo (95%CI = 1.08, 1.28); 12-15 month = 1.14 cm/3mo (95%CI = 1.02, 1.27); 15-18 months = 0.87 cm/3mo (95%CI = 0.79, 0.96); 18-21 months = 0.80 cm/3mo (95%CI = 0.72, 0.89); and 21-24 months = 0.86 cm/3mo (95%CI = 0.77, 0.96). For both boys and girls, the growth velocity in our cohort were consistently below the 3rd percentile of the WHO linear growth velocity standard. The estimated mean height and the age at which growth begins to falter were 68.6 cm (95%CI = 68.0, 69.2) and 13.6 months (95%CI = 13.2, 14.1) respectively. CONCLUSION: We found slower rate of growth among otherwise healthy Zambian infants. The data suggests that growth retardation is universal and profound in this cohort and may have already been occurring in utero.
Effect of innate antiviral glycoproteins in breast milk on seroconversion to rotavirus vaccine (Rotarix) in children in Lusaka, Zambia.
(2017) Mwila-Kazimbaya, Katayi; Garcia, Miguel P.; Bosomprah, Samuel; Laban, Natasha M.; Chisenga, Caroline C.; Permar, Sallie R.; Simuyandi, Michelo; Munsaka, Sody; Chilengi, Roma
INTRODUCTION: Rotavirus vaccines have been introduced into national immunization programmes to mitigate morbidity and mortality associated rotavirus diarrhoea. Lower vaccine effectiveness has however been noted in low-middle income countries, but little is known about the role of maternal components found in breast milk. This study assessed the effect of lactoferrin, lactadherin, and tenascin-c on rotavirus vaccine seroconversion. METHODS: This was a retrospective cohort study of 128 infants who had been fully immunized with Rotarix™. Serum samples were collected from the infant at baseline and one month after second rotavirus vaccine dose. Breast milk samples were collected from mothers at baseline. Standard ELISA was used to determine titres of rotavirus-specific immunologlobulin G and A in breast milk and serum as well as concentrations of lactoferrin, lactadherin, and tenascin-c. Poisson regression model with robust standard error was used to estimate the effect of breast milk components on seroconversion. The components were modelled on log base 2 so that the effect would be interpreted as a doubling of the concentration. RESULTS: In a multivariable analysis adjusting for maternal age, maternal HIV status, seropositivity at baseline, sex, age of child at vaccination as well as breast milk IgA and IgG, we found evidence of independent effect of LA (Adjusted IRR = 0.95; 95% CI = 0.91-0.99; P = 0.019) on seroconversion while there was no evidence for TNC (Adjusted IRR = 1.00; 95% CI = 0.85-1.17; P = 0.967) and LF (Adjusted RR = 1.01; 95% CI = 0.96-1.05); P = 0.802). We explored the joint effects of the three components but we found no evidence (Adjusted RR = 0.95; 95% CI = 0.81; P = 0.535). CONCLUSION: High breast milk concentrations of lactadherin might play a role in infant's failure to seroconvert to rotavirus vaccines. Further research to understand this observed association is an important consideration.
Evaluating the costs of cholera illness and cost-effectiveness of a single dose oral vaccination campaign in Lusaka, Zambia.
(2019) Tembo, Tannia; Simuyandi, Michelo; Chiyenu, Kanema; Sharma, Anjali; Chilyabanyama, Obvious N.; Mbwili-Muleya, Clara; Mazaba, Mazyanga L.; Chilengi, Roma
INTRODUCTION: In 2016, for the very first time, the Ministry of Health in Zambia implemented a reactive outbreak response to control the spread of cholera and vaccinated at-risk populations with a single dose of Shancol-an oral cholera vaccine (OCV). This study aimed to assess the costs of cholera illness and determine the cost-effectiveness of the 2016 vaccination campaign. METHODOLOGY: From April to June 2017, we conducted a retrospective cost and cost-effectiveness analysis in three peri-urban areas of Lusaka. To estimate costs of illness from a household perspective, a systematic random sample of 189 in-patients confirmed with V. cholera were identified from Cholera Treatment Centre registers and interviewed for out-of-pocket costs. Vaccine delivery and health systems costs were extracted from financial records at the District Health Office and health facilities. The cost of cholera treatment was derived by multiplying the subsidized cost of drugs by the quantity administered to patients during hospitalisation. The cost-effectiveness analysis measured incremental cost-effectiveness ratio-cost per case averted, cost per life saved and cost per DALY averted-for a single dose OCV. RESULTS: The mean cost per administered vaccine was US$1.72. Treatment costs per hospitalized episode were US$14.49-US$18.03 for patients ≤15 years old and US$17.66-US$35.16 for older patients. Whereas households incurred costs on non-medical items such as communication, beverages, food and transport during illness, a large proportion of medical costs were borne by the health system. Assuming vaccine effectiveness of 88.9% and 63%, a life expectancy of 62 years and Gross Domestic Product (GDP) per capita of US$1,500, the costs per case averted were estimated US$369-US$532. Costs per life year saved ranged from US$18,515-US$27,976. The total cost per DALY averted was estimated between US$698-US$1,006 for patients ≤15 years old and US$666-US$1,000 for older patients. CONCLUSION: Our study determined that reactive vaccination campaign with a single dose of Shancol for cholera control in densely populated areas of Lusaka was cost-effective.
Exploring willingness to participate in future Human Infection Studies in Lusaka, Zambia: A nested qualitative exploratory study.
(2021) Kunda-Ngándu, Evelyn M.; Chirwa-Chobe, Masuzyo; Mwamba, Chanda; Chipungu, Jenala; Ng'andu, Esnart; Chinganya, Hope M.; Simuyandi, Michelo; Chilengi, Roma; Sharma, Anjali
Human Infection Studies (HIC) involve intentional infection of volunteers with a challenge agent or pathogen with the aim of understanding and developing vaccines as well as understanding the disease pathophysiology in a well-controlled environment. Though Africa carries the highest burden of vaccine-preventable diseases, the region is only now being primed to conduct HIC relevant to its population. Given the imminent introduction of HIC in Zambia, we sought to understand potential participants' willingness to volunteer for such studies. We used a qualitative exploratory approach to understand the potential participants' perceptions on willingness to participate in HIC using the example of typhoid. Healthy adults, recruited using random selection and purposive sampling from higher learning institutions in Lusaka, participated in 15 in-depth interviews (IDIs) and 5 Focus Group Discussions (FGDs) respectively. Participants considered typhoid a serious disease with potential for life-long consequences and death. After sharing audio-visual materials introducing the concepts of HIC, some participants expressed open willingness to participate or alternatively the need to consult parents and professors, and expressed fear of death and illness. Though willing to be quarantined for up to six months, participants expressed concerns regarding separation from family and duties, having insufficient information to decide, inadequate access to care, severe disease, life-long injury or side-effects, death, and vaccine failure. These concerns along with possibility of underlying conditions that compromise individual immunity, competing priorities, parental refusal, and distrust of study or vaccine efficacy could lead to refusal to participate. Reasons for willingness to participate included monetary compensation, altruism and being part of a team that comes up with a vaccine. Though afraid of deliberate typhoid infection, potential participants are willing to consider participation if given adequate information, time to consult trusted persons, compensation and assurance of adequate care.
Genomic Analysis and Antimicrobial Resistance of Vibrio Cholerae Isolated During Zambia’s 2023 Cholera Epidemic
(2025-12-02) Ng'ombe, Harriet; Luchen, Charlie C.; Bote, Lia; Kasonde, Mpanga; Musonda, Kunda; Mwape, Kapambwe K.; Kuntawala, Dhvani H.; Silwamba, Suwilanji; Chibuye, Mwelwa; Chibesa, Kennedy; Mbewe, Nyuma; Bosomprah, Samuel; Khan, Wesaal; Liebenberg, Lenine; Oliveira, Tulio de; Wilkinson, Eduan; Dorman, Matthew J.; Coghlan, Avril; Simuyandi, Michelo; Chilengi, Roma; Chisenga, Caroline; Thomson, Nicholas R.
Introduction. Cholera, caused by Vibrio cholerae, remains a priority public health concern, particularly in developing countries. The first cholera outbreak in Zambia was documented in the 1970s, with recurring epidemics reported since then. In 2023, a cholera outbreak affected Zambia, particularly in districts bordering Malawi, Mozambique and the Democratic Republic of Congo, with significant cases reported in these neighbouring countries. This study aims to analyse cholera cases and isolates obtained during the 2023 epidemic, focusing on geographical distribution, genetic relatedness of isolates and their antibiotic resistance profiles. Methods. Stool samples were collected from patients presenting with cholera-like symptoms across three provinces of Zambia. A total of 98 samples were cultured on thiosulphate citrate bile salts sucrose agar, resulting in 32 sequenced V. cholerae isolates. Whole-genome sequencing was performed using Oxford Nanopore Technology, and phylogenetic inference was also achieved by the analysis of SNPs. Phenotypic antimicrobial resistance testing was conducted following Clinical and Laboratory Standards Institute guidelines. The genomic data were analysed for virulence factors and antimicrobial resistance profiles. Results. Of the 98 stool samples tested, 38 confirmed cholera cases were identified. A subset of 32 confirmed V. cholerae isolates, predominantly from the Eastern Province of Zambia (n=21), was selected for whole-genome sequencing. Genomic analysis revealed that all isolates belonged to the seventh pandemic El Tor lineage and the O1 serogroup, with two distinct clades identified corresponding to the 10th (T10) and 15th (T15) transmission events. Geographical analysis indicated a predominance of Ogawa serotypes in Eastern Province and Inaba in Northern Province. The virulence gene analysis confirmed the presence of key cholera toxin genes (ctxA and ctxB) and intestinal colonization factors. All isolates carried genes or mutations predicted to confer resistance to multiple antibiotics, including decreased susceptibility to ciprofloxacin, recommended for the treatment of cholera by the World Health Organization. Conclusion. The findings highlight the critical need for enhanced surveillance and targeted interventions to mitigate cholera outbreaks in Zambia. The emergence of resistant V. cholerae strains necessitates innovative strategies, including improved water sanitation, vaccination efforts and novel therapeutic approaches to combat this enduring public health threat.
Identification of cholera hotspots in Zambia: A spatiotemporal analysis of cholera data from 2008 to 2017.
(2020-Apr) Mwaba, John; Debes, Amanda K.; Shea, Patrick; Mukonka, Victor; Chewe, Orbrie; Chisenga, Caroline; Simuyandi, Michelo; Kwenda, Geoffrey; Sack, David; Chilengi, Roma; Ali, Mohammad
The global burden of cholera is increasing, with the majority (60%) of the cases occurring in sub-Saharan Africa. In Zambia, widespread cholera outbreaks have occurred since 1977, predominantly in the capital city of Lusaka. During both the 2016 and 2018 outbreaks, the Ministry of Health implemented cholera vaccination in addition to other preventative and control measures, to stop the spread and control the outbreak. Given the limitations in vaccine availability and the logistical support required for vaccination, oral cholera vaccine (OCV) is now recommended for use in the high risk areas ("hotspots") for cholera. Hence, the aim of this study was to identify areas with an increased risk of cholera in Zambia. Retrospective cholera case data from 2008 to 2017 was obtained from the Ministry of Health, Department of Public Health and Disease Surveillance. The Zambian Central Statistical Office provided district-level population data, socioeconomic and water, sanitation and hygiene (WaSH) indicators. To identify districts at high risk, we performed a discrete Poisson-based space-time scan statistic to account for variations in cholera risk across both space and time over a 10-year study period. A zero-inflated negative binomial regression model was employed to identify the district level risk factors for cholera. The risk map was generated by classifying the relative risk of cholera in each district, as obtained from the space-scan test statistic. In total, 34,950 cases of cholera were reported in Zambia between 2008 and 2017. Cholera cases varied spatially by year. During the study period, Lusaka District had the highest burden of cholera, with 29,080 reported cases. The space-time scan statistic identified 16 districts to be at a significantly higher risk of having cholera. The relative risk of having cholera in these districts was significantly higher and ranged from 1.25 to 78.87 times higher when compared to elsewhere in the country. Proximity to waterbodies was the only factor associated with the increased risk for cholera (P<0.05). This study provides a basis for the cholera elimination program in Zambia. Outside Lusaka, the majority of high risk districts identified were near the border with the DRC, Tanzania, Mozambique, and Zimbabwe. This suggests that cholera in Zambia may be linked to movement of people from neighboring areas of cholera endemicity. A collaborative intervention program implemented in concert with neighboring countries could be an effective strategy for elimination of cholera in Zambia, while also reducing rates at a regional level.
Immunogenicity of rotavirus vaccine (RotarixTM) in infants with environmental enteric dysfunction.
(2017) Mwape, Innocent; Bosomprah, Samuel; Mwaba, John; Mwila-Kazimbaya, Katayi; Laban, Natasha M.; Chisenga, Caroline C.; Sijumbila, Gibson; Simuyandi, Michelo; Chilengi, Roma
INTRODUCTION: Deployment of rotavirus vaccines has contributed to significant declines in diarrheal morbidity and mortality globally. Unfortunately, vaccine performance in low-middle income countries (LMICs) is generally lower than in developed countries. The cause for this has been associated with several host and maternal factors including poor water sanitation and hygiene (WASH) status, which are predominant in LMICs. More recently, environmental enteric dysfunction (EED) has specifically been hypothesized to contribute to poor vaccine uptake and response. The aim of this study was to examine the association between serological biomarkers of EED and seroconversion to rotavirus vaccine in Zambian infants. METHODS: This was a retrospective cohort study of 142 infants who had been fully immunized with Rotarix™, and had known seroconversion status. Seroconversion was defined as 4-fold or more increase in rotavirus-specific IgA titres between pre-vaccination and one month post-dose two vaccination. We performed ELISA assays to assess soluble CD14 (sCD14), Endotoxin Core IgG Antibodies (EndoCAb), intestinal fatty acid binding protein (i-FABP) and Zonulin according to the manufacturers protocols. Generalised linear model with family-poisson, link-log and robust standard error was used to estimate the independent effects of biomarkers on seroconversion adjusting for important cofounders. RESULTS: The median concentration of Zonulin, Soluble CD14, EndoCaB, and IFABP were 209.3 (IQR = 39.7, 395.1), 21.5 (IQR = 21.5, 21.5), 0.3 (IQR = 0.3, 0.3), and 107.7 (IQR = 6.4, 1141.4) respectively. In multivariable analyses adjusting for the independent effect of other biomarkers and confounders (i.e. age of child at vaccination, breast-milk anti-rotavirus IgA, infant serum anti-rotavirus IgG, and IgA seropositivity at baseline), there was strong evidence of about 24% increase in seroconversion due to doubling Zonulin concentration (Adjusted risk ratio (aRR) = 1.24; 95% CI = 1.12 to1.37; p<0.0001). Similarly, we found about 7% increase in seroconversion due to doubling IFABP concentration (aRR = 1.07; 95% CI = 1.02 to 1.13; p = 0.006). CONCLUSION: We found that high levels of zonulin and IFABP played a role in seroconversion. It is plausible that increased gut permeability in EED allows greater uptake of the live virus within the vaccine, but later consequences result in deleterious local structural distortions and malabsorption syndromes.
In-vitro inhibitory effect of maternal breastmilk components on rotavirus vaccine replication and association with infant seroconversion to live oral rotavirus vaccine.
(2020) Kazimbaya, Katayi M.; Chisenga, Caroline C.; Simuyandi, Michelo; Phiri, Cynthia M.; Laban, Natasha M.; Bosomprah, Samuel; Permar, Sallie R.; Munsaka, Sody; Chilengi, Roma
BACKGROUND: Despite contributing to a significant reduction in rotavirus associated diarrhoea in highly burdened low- and middle-income countries, live attenuated, oral rotavirus vaccines have lower immunogenicity and efficacy in these settings in comparison to more developed countries. Breastmilk has been implicated among factors contributing to this lowered oral vaccine efficacy. We conducted in-vitro experiments to investigate the inhibitory effects of maternal antibody and other non-antibody components in breastmilk on rotavirus vaccine strain (Rotarix) multiplication in MA104 cell culture system and assessed associations with in-vivo vaccine seroconversion in vaccinated infants. METHODS: Breastmilk samples were collected from mothers before routine rotavirus vaccination of their infant at 6 weeks of age. For each sample, whole breastmilk, purified IgA, purified IgG and IgG and IgA depleted breastmilk samples were prepared as exposure preparations. A 96 well microtitre plate was set up for each sample including a control in which only MA104 cells were grown as well as a virus control with MA104 cells and virus only. The outcome of interest was 50% inhibition dilution of each of the exposure preparations calculated as the titer at which 50% of virus dilution was achieved. Samples from 30 women were tested and correlated to vaccine seroconversion status of the infant. HIV status was also correlated to antiviral breastmilk proteins. RESULTS: The mean 50% inhibitory dilution titer when whole breastmilk was added to virus infected MA104 cells was 14.3 (95% CI: 7.1, 22.7). Incubation with purified IgG resulted in a mean 50% inhibitory dilution of 5 (95%CI -1.6, 11.6). Incubating with purified IgA resulted in a mean 50% inhibitory dilution of 6.5 (95% CI -0.7, 13.7) and IgG and IgA depleted breastmilk did not yield any inhibition with a titer of 1.06 (95%CI 0.9, 1.2). Higher milk IgA levels contributed to a failure of infants to seroconvert. HIV was also not associated with any antiviral breastmilk proteins. DISCUSSION AND CONCLUSION: Whole breastmilk and breastmilk purified IgG and IgA fractions showed inhibitory activity against the rotavirus vaccine Rotarix™ whilst IgA and IgG depleted breastmilk with non-antibody breastmilk fraction failed to show any inhibition activity in-vitro. These findings suggest that IgA and IgG may have functional inhibitory properties and indicates a possible mechanism of how mothers in rotavirus endemic areas with high titres of IgA and IgG may inhibit viral multiplication in the infant gut and would potentially contribute to the failure of their infants to serocovert. There was not association of HIV with either lactoferrin, lactadherin or tenascin-C concentrations.
Norovirus infections in young children in Lusaka Province, Zambia: clinical characteristics and molecular epidemiology.
(2017-Jan-23) Howard, Leigh M.; Mwape, Innocent; Siwingwa, Mpanji ; Simuyandi, Michelo; Guffey, Brad M.; Stringer, Jeffrey S.; Chi, Benjamin H.; Edwards, Kathryn M.; Chilengi, Roma
BACKGROUND: The burden, clinical features, and molecular epidemiology of norovirus infection in young children in southern Africa are not well defined. METHODS: Using data from a health facility-based surveillance study of children <5 years in Lusaka Province, Zambia presenting with diarrhea, we assessed the burden of norovirus infection. A convenience sample of 454 stool specimens was tested for norovirus using reverse-transcriptase polymerase chain reaction (RT-PCR). RT-PCR positive samples underwent additional nucleotide sequencing for genogroup and genotype identification. Clinical features and severity of diarrheal illnesses were compared between norovirus-positive and -negative subjects using Chi-squared and t-tests. RESULTS: Norovirus was detected in 52/454 (11.5%) specimens tested. Abdominal pain, fever, and vomiting were the most common presenting features in norovirus-associated illnesses. However, there were no significant differences in the clinical features of norovirus-positive compared to norovirus-negative illnesses. Of 43 isolates that were available for sequencing, 31 (72.1%) were genogroup II (GII) and 12 (27.9%) were genogroup I (GI). The distribution of genotypes was diverse. CONCLUSIONS: Noroviruses were detected in approximately 10% of young children with diarrhea in the Lusaka Province of Zambia, with GII representing the majority of infections. These findings support the role of norovirus in symptomatic diarrhea disease in Africa. Further studies are needed to confirm these observations and to evaluate prevention strategies.
Nutritional status, environmental enteric dysfunction, and prevalence of rotavirus diarrhoea among children in Zambia.
(2020) Koyuncu, Aybuke; Simuyandi, Michelo; Bosomprah, Samuel; Chilengi, Roma
BACKGROUND: Rotavirus is the most common cause of fatal diarrhoeal disease among children under the age of five globally and is responsible for millions of hospitalizations each year. Although nutritional status and environmental enteric dysfunction (EED) are recognized as important predictors of susceptibility to diarrhoeal disease, no research to date has examined the mechanisms by which undernutrition and EED may protect against prevalence of rotavirus infection. METHODS: We utilized data collected from a study evaluating the effectiveness of Rotarix™ vaccine against severe gastroenteritis among children under the age of 5 in Zambia. The prevalence of malnutrition, wasting, and stunting at the time of study enrollment was calculated using WHO child growth standards. Commercial ELISA kits were used to assess levels of faecal biomarkers for EED: alpha-1-antitrypsin and myeloperoxidase, and calprotectin. Separate multivariate logistic regression models were used to examine each measure of nutritional status and rotavirus diarrhoea including and excluding adjustment for EED. RESULTS: In models that did not include adjustment for EED, malnourished children had 0.66 times the odds of having rotavirus diarrhoea compared to children with normal nutritional status (95% CI: 0.42, 1.0; p = 0.07). EED severity score was significantly higher among controls asymptomatic for diarrhoeal disease compared to cases with rotavirus diarrhoea (p = 0.02). CONCLUSION: The morphological changes associated with EED may confer protection against rotavirus infection and subsequent diarrhoeal disease among children. Further research is critically needed to better understand the complex mechanisms by which nutritional status and EED may impact susceptibility to rotavirus in early life.
Prevalence and Patterns of Enteric Co-Infections Among Individuals Presenting with Cholera-like Diarrheal Disease During Seasonal Cholera Outbreaks
(Pathogens, 2025-11-30) Kuntawala, Dhvani H.; Bosomprah, Samuel; Phiri, Bernard; Ng’ombe, Harriet; Liswaniso, Fraser; Muchimba, Mutinta; Silwamba, Suwilanji; Chibesa, Kennedy; Nzangwa, Bertha T.; Luchen, Charlie C.; Mwape, Innocent; Tigere, Sekayi F.; Simuyandi, Michelo; Mbewe, Nyuma; Chilengi, Roma; Debes, Amanda K.; Thomson, Nicholas R.; Sack, David A.; Chisenga, Caroline C.
Abstract Cholera remains a major public health challenge, and co-infections can complicate clinical outcomes. In a cross-sectional study, we investigated the prevalence and patterns of enteric co-infections during Zambia’s 2023–2024 cholera outbreak and evaluated their implications for disease severity. 240 suspected cholera patients were enrolled from five healthcare facilities in Lusaka. Stools were tested for 11 enteric pathogens using the Bosphore® Gastroenteritis Panel Kit v2 on the QuantStudio 5 qPCR, with Vibrio cholerae confirmed by real-time PCR (quantitative PCR). Co-infections were highly prevalent, affecting 79.2% of participants. Campylobacter was the most frequently detected pathogen (70.0%), followed by Norovirus GI/GII (20.0%). Persons living with HIV were significantly more likely to present with co-infections than their counterparts (adjusted PR 1.27, 95% CI: 1.07–1.51; p = 0.008). Participants with confirmed V. cholerae + coinfections (N = 62) were less likely to developed moderate to severe disease compared to those with mono-infections (adjusted PR 0.59, 95% CI: 0.38–0.90; p = 0.014). These findings highlight the high prevalence and complexity of co-infections during cholera outbreaks, potentially contributing to antimicrobial resistance. They also highlight the need for targeted clinical management, particularly among persons living with HIV.
Rotavirus Prevalence, Genetic Diversity, and Co-Infections during the 2023- 2024 Cholera Outbreak in Zambia: Insights from Multi-Pathogen Diagnostics
(2026-02-28) Chauwa, Adriace; Bosomprah, Samuel; Phiri, Bernard; Laban, Natasha M.; Kuntawala, Dhvani H.; Ngosa, Dennis; Ng'ombe, Harriet; Liswaniso, Fraser; Luchen, Chaluma C.; Muchimba, Mutinta; Mwape, Innocent; Nzangwa, Bertha T.; Tigere, Sekayi F.; Chibesa, Kennedy; Silwamba, Suwilanji; Simuyandi, Michelo; Mbewe, Nyuma; Chilengi, Roma; Chisenga, Caroline C.
Abstract During cholera outbreaks in Zambia, diagnostic strategies that rely on single-plex or targeted assays risk overlooking concomitant infections with other clinically important enteric pathogens. We estimated the prevalence of rotavirus and described co-detected enteropathogens and rotavirus genotypes among patients admitted with clinically suspected cholera during Zambia’s 2023–2024 cholera outbreak. We conducted a sub-analysis of diarrhoeal specimens collected from patients admitted to five cholera treatment centres who met the syndromic suspected cholera case definition. Stool samples were tested using the Bosphore® Gastroenteritis Panel v2, a multiplex PCR enteric panel, to detect rotavirus and other gastrointestinal pathogens. Rotavirus-positive specimen with sufficient viral load were further characterised by RT-PCR genotyping and Sanger sequencing targeting VP7 and VP4 genes. Among 319 suspected cholera admissions, rotavirus was detected in 18 patients, yielding a prevalence of 5.6% (95% CI 3.4%, 8.8%). Rotavirus detections occurred predominantly in children aged <5 years (87.5%) and 6-15 years (80.0%). Co-infection was common - 93.7%, (15/16) of rotavirus-positive samples showed co-infection with at least one additional enteric pathogen, primarily Campylobacter. Genotyping was successful in five samples and showed heterogenous circulating strains, including G1P[8], G2P[4], G3P[6], G12P[6], and a rare G1P[6] reassortant. During a large 2023–2024 cholera outbreak in Zambia, rotavirus accounted for a modest but clinically important fraction of the suspected cholera admissions and was typically identified within mixed enteric infections. These findings highlight the limitations of syndromic diagnosis in outbreak settings and support integrating multi-pathogen diagnostics and sustained molecular surveillance to improve case management, antimicrobial stewardship, and vaccine-era monitoring.
Serum vibriocidal responses when second doses of oral cholera vaccine are delayed 6 months in Zambia.
(2021-Jul-22) Mwaba, John; Chisenga, Caroline C.; Xiao, Shaoming; Ng'ombe, Harriet; Banda, Elena; Shea, Patrick; Mabula-Bwalya, Chileshe; Mwila-Kazimbaya, Katayi; Laban, Natasha M.; Alabi, Peter; Chirwa-Chobe, Masuzyo; Simuyandi, Michelo; Harris, Jason; Iyer, Anita S.; Bosomprah, Samuel; Scalzo, Paul; Murt, Kelsey N.; Ram, Malathi ; Kwenda, Geoffrey; Ali, Mohammad; Sack, David A.; Chilengi, Roma; Debes, Amanda K.
Two-dose killed oral cholera vaccines (OCV) are currently being used widely to control cholera. The standard dose-interval for OCV is 2 weeks; however, during emergency use of the vaccine, it may be more appropriate to use the available doses to quickly give a single dose to more people and give a delayed second dose when more vaccine becomes available. This study is an open label, randomized, phase 2 clinical trial of the vibriocidal response induced by OCV, comparing the responses when the second dose was given either 2 weeks (standard dose interval) or 6 months (extended dose interval) after the first dose. Vaccine was administered to healthy participants > 1 year of age living in the Lukanga Swamps area of Zambia. Three age cohorts (<5 years, 5-14 years, and ≥ 15 years) were randomized to the either dose-interval. The primary outcome was the vibriocidal GMT 14 days after the second dose. 156 of 172 subjects enrolled in the study were included in this analysis. The Inaba vibriocidal titers were not significantly different 14 days post dose two for a standard dose-interval GMT: 45.6 (32-64.9), as compared to the GMT 47.6 (32.6-69.3), for the extended dose-interval, (p = 0.87). However, the Ogawa vibriocidal GMTs were significantly higher 14 days post dose two for the extended-dose interval at 87.6 (58.9-130.4) compared to the standard dose-interval group at 49.7 (34.1-72.3), p = 0.04. Vibriocidal seroconversion rates (a > 4-fold rise in vibriocidal titer) were not significantly different between dose-interval groups. This study demonstrated that vibriocidal titers 14 days after a second dose when given at an extended\ dose interval were similar to the standard dose-interval. The findings suggest that a flexible dosing schedule may be considered when epidemiologically appropriate. The trial was registered at Clinical Trials.gov (NCT03373669).
Shigella-specific antibodies in the first year of life among Zambian infants: A longitudinal cohort study.
(2021) Chisenga, Caroline C.; Bosomprah, Samuel; Simuyandi, Michelo; Mwila-Kazimbaya, Katayi; Chilyabanyama, Obvious N.; Laban, Natasha M.; Bialik, Anya; Asato, Valeria; Meron-Sudai, Shiri; Frankel, Gad; Cohen, Daniel; Chilengi, Roma
INTRODUCTION: Shigellosis, is a leading cause of moderate-to-severe diarrhoea and related mortality in young children in low and middle income countries (LMICs). Knowledge on naturally acquired immunity can support the development of Shigella candidate vaccines mostly needed in LMICs. We aimed to quantify Shigella-specific antibodies of maternal origin and those naturally acquired in Zambian infants. METHODS: Plasma samples collected from infants at age 6, 14 and 52-weeks were tested for Shigella (S. sonnei and S. flexneri 2a) lipopolysaccharide (LPS) antigen specific immunoglobulin G (IgG) and A (IgA) by enzyme-linked immunosorbent assay. RESULTS: At 6 weeks infant age, the IgG geometric mean titres (GMT) against S. sonnei (N = 159) and S. flexneri 2a (N = 135) LPS were 311 (95% CI 259-372) and 446 (95% CI 343-580) respectively. By 14 weeks, a decline in IgG GMT was observed for both S. sonnei to 104 (95% CI 88-124), and S. flexneri 2a to 183 (95% CI 147-230). Both S. sonnei and S. flexneri 2a specific IgG GMT continued to decrease by 52 weeks infant age when compared to 6 weeks. In 27% and 8% of infants a significant rise in titre (4 fold and greater) against S. flexneri 2a and S. sonnei LPS, respectively, was detected between the ages of 14 and 52 weeks. IgA levels against both species LPS were very low at 6 and 14 weeks and raised significantly against S. flexneri 2a and S. sonnei LPS in 29% and 10% of the infants, respectively. CONCLUSION: In our setting, transplacental IgG anti-Shigella LPS is present at high levels in early infancy, and begins to decrease by age 14 weeks. Our results are consistent with early exposure to Shigella and indicate naturally acquired IgG and IgA antibodies to S. flexneri 2a and S. sonnei LPS in part of infants between 14 and 52 weeks of age. These results suggest that a potential timing of vaccination would be after 14 and before 52 weeks of age to ensure early infant protection against shigellosis.
Systematic review of associations between gut microbiome composition and stunting in under-five children.
(2024-May-23) Chibuye, Mwelwa; Mende, Daniel R.; Spijker, Rene; Simuyandi, Michelo; Luchen, Chaluma C.; Bosomprah, Samuel; Chilengi, Roma; Schultsz, Constance; Harris, Vanessa C.
Childhood stunting is associated with impaired cognitive development and increased risk of infections, morbidity, and mortality. The composition of the enteric microbiota may contribute to the pathogenesis of stunting. We systematically reviewed and synthesized data from studies using high-throughput genomic sequencing methods to characterize the gut microbiome in stunted versus non-stunted children under 5 years in LMICs. We included 14 studies from Asia, Africa, and South America. Most studies did not report any significant differences in the alpha diversity, while a significantly higher beta diversity was observed in stunted children in four out of seven studies that reported beta diversity. At the phylum level, inconsistent associations with stunting were observed for Bacillota, Pseudomonadota, and Bacteroidota phyla. No single genus was associated with stunted children across all 14 studies, and some associations were incongruent by specific genera. Nonetheless, stunting was associated with an abundance of pathobionts that could drive inflammation, such as Escherichia/Shigella and Campylobacter, and a reduction of butyrate producers, including Faecalibacterium, Megasphera, Blautia, and increased Ruminoccoccus. An abundance of taxa thought to originate in the oropharynx was also reported in duodenal and fecal samples of stunted children, while metabolic pathways, including purine and pyrimidine biosynthesis, vitamin B biosynthesis, and carbohydrate and amino acid degradation pathways, predicted linear growth. Current studies show that stunted children can have distinct microbial patterns compared to non-stunted children, which could contribute to the pathogenesis of stunting.
Three transmission events of Vibrio cholerae O1 into Lusaka, Zambia.
(2021-Jun-14) Mwaba, John; Debes, Amanda K.; Murt, Kelsey N.; Shea, Patrick; Simuyandi, Michelo; Laban, Natasha; Kazimbaya, Katayi; Chisenga, Caroline; Li, Shan; Almeida, Mathieu; Meisel, Jacquelyn S.; Shibemba, Aaron; Kantenga, Timothy; Mukonka, Victor; Kwenda, Geoffrey; Sack, David A.; Chilengi, Roma; Stine, Colin O.
BACKGROUND: Cholera has been present and recurring in Zambia since 1977. However, there is a paucity of data on genetic relatedness and diversity of the Vibrio cholerae isolates responsible for these outbreaks. Understanding whether the outbreaks are seeded from existing local isolates or if the outbreaks represent separate transmission events can inform public health decisions. RESULTS: Seventy-two V. cholerae isolates from outbreaks in 2009/2010, 2016, and 2017/2018 in Zambia were characterized using multilocus variable number tandem repeat analysis (MLVA) and whole genome sequencing (WGS). The isolates had eight distinct MLVA genotypes that clustered into three MLVA clonal complexes (CCs). Each CC contained isolates from only one outbreak. The results from WGS revealed both clustered and dispersed single nucleotide variants. The genetic relatedness of isolates based on WGS was consistent with the MLVA, each CC was a distinct genetic lineage and had nearest neighbors from other East African countries. In Lusaka, isolates from the same outbreak were more closely related to themselves and isolates from other countries than to isolates from other outbreaks in other years. CONCLUSIONS: Our observations are consistent with i) the presence of random mutation and alternative mechanisms of nucleotide variation, and ii) three separate transmission events of V. cholerae into Lusaka, Zambia. We suggest that locally, case-area targeted invention strategies and regionally, well-coordinated plans be in place to effectively control future cholera outbreaks.