Interferon-gamma responses to Plasmodium falciparum liver-stage antigen-1 and merozoite-surface protein-1 increase with age in children in a malaria holoendemic area of western Kenya

BACKGROUND: In areas of high-level, year-round malaria transmission, morbidity and mortality due to malaria decrease after the first two to three years of life. This reduction may be related to the development of cellular immunity to specific antigens expressed in the different life-cycle stages of Plasmodium falciparum. METHODS: A cross sectional study was conducted to evaluate T cell cytokine responses to the P. falciparum pre-erythrocytic antigen liver-stage antigen-1 (LSA-1) and the blood-stage antigen merozoite-surface protein-1 (MSP-1) in children under five years of age residing in a malaria holoendemic region of western Kenya. Interferon-γ (IFN-γ) and interleukin-10 (IL-10) responses to the LSA-1 T3 peptide (aa 1813–1835) and the MSP-1 aa20–39 peptide were tested in 48 children. RESULTS: The proportion of children producing IFN-γ to LSA-1 and to MSP-1 increased with age: in the 0–12, 13–24, 25–36 and 37–48 month age groups, zero, 11.1, 36.4 and 40% of children had IFN-γ responses to LSA-1 (p = 0.019), and 10, 10, 27.7 and 40% of children had IFN-γ responses to MSP-1 (p = 0.07), respectively. In contrast, the proportion of children producing IL-10 to LSA-1 and MSP-1 was similar in all age groups. CONCLUSION: The data suggest that development of IFN-γ responses to LSA-1 and MSP-1 requires increased age and/or repeated exposure, whereas IL-10 responses to these antigens may occur at any age and with limited exposure. The data also demonstrate that by the age of 4 years, children in a malaria holoendemic area develop frequencies of IFN-γ responses to LSA-1 and MSP-1 similar to those seen in adults in the area

Drug resistant tuberculosis in Kenya: trends, characteristics and treatment outcomes, 2008 – 2016

Background: Drug resistant (DR) tuberculosis (TB) remains a major public health concern. Failure to treat patients with TB adequately increases the risk of transmission of infection to the general population. Treatment of DR TB is characterized by lengthy treatment duration, use of toxic and less effective drugs and high likelihood of adverse treatment outcomes that include adverse drug reactions, high mortality and loss to follow up.Objective: To determine the trends, characteristics and treatment outcomes of patients >15 years notified with DR‐TB in Kenya from 2008 to 2016Design: Retrospective descriptive cross‐sectional studySetting: Tuberculosis treatment centers in KenyaSubjects: Persons above 15 years notified with DR TBResults: We reviewed records of 1903 DR‐TB patients who were notified between 2008 and 2016. The public sector made the highest contribution of the notified cases (80%). Most of the cases were male (62.3%). The HIV testing rate was 99.5%, with the TB/HIV co‐infection being 36%. Initiation of antiretroviral therapy among those who tested positive for HIV was 94.6%. Co‐trimoxazole preventive therapy uptake was 99.3%. Most patients had secondary DRTB (77.3%). Multi‐drug resistant TB accounted for 78.4% of the DR TB cases while mono drug resistance was observed in 26% of the cases. Treatment success was achieved in 79% of the cases. Mortality and treatment failure during the study period was 11% and 0.2% respectively.Conclusion: An upward trend in notified DR‐TB cases was observed during the period under review. The public sector gave the most contribution. Active surveillance on patients lost to follow up while on treatment and poor drug adherence will be of importance to reduce the potential of development of drug resistance

Identification of a novel variant of LMP-1 of EBV in patients with endemic Burkitt lymphoma in western Kenya

BACKGROUND: Epstein Barr virus (EBV) is a gammaherpesvirus that is associated with nasopharyngeal carcinoma (NPC) and endemic Burkitt lymphoma (eBL). EBV carries several latent genes that contribute to oncogenesis including the latent membrane protein 1 (LMP-1), a known oncogene and constitutively active CD40 homolog. Variation in the C terminal region of LMP-1 has been linked to NPC pathogenesis, but little is known regarding LMP-1 variation and eBL. RESULTS: In the present study, peripheral blood samples were obtained from 38 eBL patients and 22 healthy controls in western Kenya, where the disease is endemic. The LMP-1 C-terminal region from these samples was sequenced and analyzed. The frequency of a 30 base pair deletion of LMP-1 previously linked to NPC was not associated with eBL compared to healthy controls. However a novel LMP-1 variant was identified, called K for Kenya and for the G318K mutation that characterizes it. The K variant LMP-1 was found in 40.5% of eBL sequences and 25.0% of healthy controls. All K variant sequences contained mutations in both of the previously described minimal T cell epitopes in the C terminal end of LMP-1. These mutations occurred in the anchor residue at the C-terminal binding groove of both epitopes, a pocket necessary for MHC loading. CONCLUSIONS: Overall, our results suggest that there is a novel K variant of LMP-1 in Kenya that may be associated with eBL. Further studies are necessary to determine the functional implications of the LMP-1 variant on early events in eBL genesis

Outcomes of Kenyan children under five years of age, initiated on isoniazid preventive therapy following exposure to bacteriologically confirmed pulmonary tuberculosis, 2013-2016

Background: Isoniazid preventive therapy (IPT) is one of the key interventions in achieving the End TB Strategy of 90% reduction in Tuberculosis (TB) incidence by 2030 compared with 2015. One of the key pillars in achieving this is preventive treatment of persons at high risk of contracting TB. This group includes children less than five years exposed to bacteriologically confirmed TB. Despite Kenya national IPT roll out in 2015, there still exists limited information on its programmatic coverage, outcomes and missed opportunities for initiation of IPT.Objective: To determine the coverage, outcomes and missed opportunities for initiation of IPT among children under-five years in contact with bacteriologically confirmed pulmonary tuberculosis (PTB) in Kenya.Design: Cross sectional descriptive study.Setting: All the 47 counties in Kenya.Subjects: Children under-five years exposed to bacteriologically confirmed PTB initiated on IPT and notified between 2013 and 2016.Results: During the study period (2013-2016), a total of 6,507 children aged less than five years who were exposed to bacteriologically confirmed PTB were initiated on IPT. The number of children initiated on IPT increased from 721 in 2013 to 3306 in 2016.The number of counties notifying cases increased from 26 in 2013 to 47 in 2016. Treatment completion was 78%, 87% and 82% for 2013, 2014 and 2015 respectively. Of the 1390 children who had completed the 6 month-course of IPT during the study period, 9%had no TB, 7% were not accessed while84% had no documentation of outcomes by the end of the follow up period of 24 months. Missed opportunities for initiation of IPT reduced from 90% (7109) in 2013 to 60% (4872) in 2016.Conclusion: IPT coverage and completion rates have improved from 721 in 2013 to 3306 in 2016 and 78% in 2013 to 82% in 2015 respectively. Despite this, Kenya is yet to meet the targets set by the World Health Organization (WHO). Sustainable measures need to be put in place to achieve the WHO targets

Spatial and temporal distribution of notified tuberculosis cases in Nairobi County, Kenya, between 2012 and 2016

Background: Tuberculosis (TB) is an infectious disease of major public health concern globally. The disease has showed space‐time variations across settings. Spatial temporal assessment can be used to understand the distribution and variations of TB disease.Objective: To determine the spatial and temporal distribution of notified TB cases in Nairobi County, Kenya, between 2012 and 2016Design: A cross sectional studySetting: Nairobi County, KenyaSubjects: Tuberculosis cases notified in Tuberculosis Information for Basic Units from 2012 to 2016Results: A total of 70,505 cases of TB were notified in Nairobi County between 2012 and 2016, with male to female ratio of 3:2 and HIV coinfection rate of 38%.The temporal analysis showed a declining trend of the notified cases. The spatial clusters showed stability in most areas while others varied annually during the study period. The space‐time analysis also detected the four most likely clusters or hotspots. Cluster 1 which covered the informal settlements of Kibera, Kawangware and Kangemi with 4,011observed cases against 2,977expected notified TB cases(relative risk (RR) 1.37, p<0.001). Further, Cluster 2 covered Starehe and parts of Kamukunji, Mathare, Makadara, Kibra and Dagoretti North Constituencies (RR 1.93, p<0.001; observed and expected cases were 4,206 and 2,242, respectively.Conclusion: This study identified high TB case notifications, declining temporal trends and clustering of TB cases in Nairobi. Evidence of clustering of TB cases indicates the need for focused interventions in the hotspot areas. Strategies should be devised for continuous TB surveillance and evidence based decision making

Recurrent Plasmodium falciparum Malaria Infections in Kenyan Children Diminish T-Cell Immunity to Epstein Barr Virus Lytic but Not Latent Antigens

Plasmodium falciparum malaria (Pf-malaria) and Epstein Barr Virus (EBV) infections coexist in children at risk for endemic Burkitt's lymphoma (eBL); yet studies have only glimpsed the cumulative effect of Pf-malaria on EBV-specific immunity. Using pooled EBV lytic and latent CD8+ T-cell epitope-peptides, IFN-γ ELISPOT responses were surveyed three times among children (10 months to 15 years) in Kenya from 2002–2004. Prevalence ratios (PR) and 95% confidence intervals (CI) were estimated in association with Pf-malaria exposure, defined at the district-level (Kisumu: holoendemic; Nandi: hypoendemic) and the individual-level. We observed a 46% decrease in positive EBV lytic antigen IFN-γ responses among 5–9 year olds residing in Kisumu compared to Nandi (PR: 0.54; 95% CI: 0.30–0.99). Individual-level analysis in Kisumu revealed further impairment of EBV lytic antigen responses among 5–9 year olds consistently infected with Pf-malaria compared to those never infected. There were no observed district- or individual-level differences between Pf-malaria exposure and EBV latent antigen IFN-γ response. The gradual decrease of EBV lytic antigen but not latent antigen IFN-γ responses after primary infection suggests a specific loss in immunological control over the lytic cycle in children residing in malaria holoendemic areas, further refining our understanding of eBL etiology

The Breadth, but Not the Magnitude, of Circulating Memory B Cell Responses to P. falciparum Increases with Age/Exposure in an Area of Low Transmission

BACKGROUND: Malaria caused by Plasmodium falciparum remains a major cause of death in sub-Saharan Africa. Immunity against symptoms of malaria requires repeated exposure, suggesting either that the parasite is poorly immunogenic or that the development of effective immune responses to malaria may be impaired. METHODS: We carried out two age-stratified cross-sectional surveys of anti-malarial humoral immune responses in a Gambian village where P. falciparum malaria transmission is low and sporadic. Circulating antibodies and memory B cells (MBC) to four malarial antigens were measured using ELISA and cultured B cell ELISpot. FINDINGS AND CONCLUSIONS: The proportion of individuals with malaria-specific MBC and antibodies, and the average number of antigens recognised by each individual, increased with age but the magnitude of these responses did not. Malaria-specific antibody levels did not correlate with either the prevalence or median number of MBC, indicating that these two assays are measuring different aspects of the humoral immune response. Among those with immunological evidence of malaria exposure (defined as a positive response to at least one malarial antigen either by ELISA or ELISPOT), the median number of malaria-specific MBC was similar to median numbers of diphtheria-specific MBC, suggesting that the circulating memory cell pool for malaria antigens is of similar size to that for other antigens

Antibody-Mediated Growth Inhibition of Plasmodium falciparum: Relationship to Age and Protection from Parasitemia in Kenyan Children and Adults

BACKGROUND: Antibodies that impair Plasmodium falciparum merozoite invasion and intraerythrocytic development are one of several mechanisms that mediate naturally acquired immunity to malaria. Attempts to correlate anti-malaria antibodies with risk of infection and morbidity have yielded inconsistent results. Growth inhibition assays (GIA) offer a convenient method to quantify functional antibody activity against blood stage malaria. METHODS: A treatment-time-to-infection study was conducted over 12-weeks in a malaria holoendemic area of Kenya. Plasma collected from healthy individuals (98 children and 99 adults) before artemether-lumefantrine treatment was tested by GIA in three separate laboratories. RESULTS: Median GIA levels varied with P. falciparum line (D10, 8.8%; 3D7, 34.9%; FVO, 51.4% inhibition). The magnitude of growth inhibition decreased with age in all P. falciparum lines tested with the highest median levels among children \u3c4 years compared to adults (e.g. 3D7, 45.4% vs. 30.0% respectively, p = 0.0003). Time-to-infection measured by weekly blood smears was significantly associated with level of GIA controlling for age. Upper quartile inhibition activity was associated with less risk of infection compared to individuals with lower levels (e.g. 3D7, hazard ratio = 1.535, 95% CI = 1.012-2.329; p = 0.0438). Various GIA methodologies had little effect on measured parasite growth inhibition. CONCLUSION: Plasma antibody-mediated growth inhibition of blood stage P. falciparum decreases with age in residents of a malaria holoendemic area. Growth inhibition assay may be a useful surrogate of protection against infection when outcome is controlled for age