Longitudinal Study of Selected Bacterial Zoonoses in Small Ruminants in Tana River County, Kenya

Brucellosis, Q fever, and leptospirosis are priority zoonoses worldwide, yet their epidemiology is understudied, and studies investigating multiple pathogens are scarce. Therefore, we selected 316 small ruminants in irrigated, pastoral, and riverine settings in Tana River County and conducted repeated sampling for animals that were initially seronegative between September 2014 and June 2015. We carried out serological and polymerase chain reaction tests and determined risk factors for exposure. The survey-weighted serological incidence rates were 1.8 (95% confidence intervals [CI]: 1.3–2.5) and 1.3 (95% CI: 0.7–2.3) cases per 100 animal-months at risk for Leptospira spp. and C. burnetii, respectively. We observed no seroconversions for Brucella spp. Animals from the irrigated setting had 6.83 (95% CI: 2.58–18.06, p-value = 0.01) higher odds of seropositivity to C. burnetii than those from riverine settings. Considerable co-exposure of animals to more than one zoonosis was also observed, with animals exposed to one zoonosis generally having 2.5 times higher odds of exposure to a second zoonosis. The higher incidence of C. burnetii and Leptospira spp. infections, which are understudied zoonoses in Kenya compared to Brucella spp., demonstrate the need for systematic prioritization of animal diseases to enable the appropriate allocation of resources

Longitudinal Study of Selected Bacterial Zoonoses in Small Ruminants in Tana River County, Kenya

Brucellosis, Q fever, and leptospirosis are priority zoonoses worldwide, yet their epidemiology is understudied, and studies investigating multiple pathogens are scarce. Therefore, we selected 316 small ruminants in irrigated, pastoral, and riverine settings in Tana River County and conducted repeated sampling for animals that were initially seronegative between September 2014 and June 2015. We carried out serological and polymerase chain reaction tests and determined risk factors for exposure. The survey-weighted serological incidence rates were 1.8 (95% confidence intervals [CI]: 1.3-2.5) and 1.3 (95% CI: 0.7-2.3) cases per 100 animal-months at risk for Leptospira spp. and C. burnetii, respectively. We observed no seroconversions for Brucella spp. Animals from the irrigated setting had 6.83 (95% CI: 2.58-18.06, p-value = 0.01) higher odds of seropositivity to C. burnetii than those from riverine settings. Considerable co-exposure of animals to more than one zoonosis was also observed, with animals exposed to one zoonosis generally having 2.5 times higher odds of exposure to a second zoonosis. The higher incidence of C. burnetii and Leptospira spp. infections, which are understudied zoonoses in Kenya compared to Brucella spp., demonstrate the need for systematic prioritization of animal diseases to enable the appropriate allocation of resources

Inter-epidemic Rift Valley fever virus seropositivity in an irrigation scheme in Bura, southeast Kenya

Rift Valley Fever (RVF) is an acute mosquito-borne viral zoonosis that causes cyclical epidemics in sub-Saharan Africa, with recent incursions into the Arabian Peninsula. Outbreaks of RVF are associated with above average rainfall and flooding, in which large numbers of vectors emerge. Recent studies into the interepidemic maintenance of RVF virus (RVFV) suggest that both vertical transmission in vectors and direct transmission between hosts, in combination with predisposing ecosystems, are responsible for persistence of the virus. A longitudinal survey was carried out in Tana River County, Kenya, in three ecosystems (irrigated, riverine and pastoral) from September 2014 – June 2015. The objectives of the study were to investigate possibility of low-level RVFV transmission during an inter-epidemic period, to examine variation in RVFV seroprevalence in sheep and goats across these ecosystems and to determine the risk factors for RVFV transmission. 316 small ruminants were selected and tested for immunoglobulin G antibodies against RVFV nucleoprotein using a competitive ELISA during 6 visits. Data on potential risk factors was also captured. The overall RVF virus seropositivity was 12.3% (95%CI = 9%-16.6%) by the end of the study. This varied across the sampling sites with the pastoral ecosystem having a significantly higher seroprevalence at 26.1% (95%CI = 16.6%-38.3%, p0.05) in the irrigated area (7) and in the riverine area (11). Seroconversions were significantly associated with presence of water either due to rainfall or irrigation (p<0.05). This study indicates that RVFV is circulating in the studied area. It also highlights the risk posed by land use changes, such as the creation and expansion of irrigation schemes, in increasing the risk of inter-epidemic RVFV transmission. This is through provision of necessary environmental conditions for vegetative growth thus providing vectors with more breeding grounds, shade and resting places, which further prolong their lifespans thereby propagating the virus. The findings provide policy makers with the evidence needed for vector and RVF prevention and control within this changing environment

An updated atlas of human helminth infections: the example of East Africa.

BACKGROUND: Reliable and updated maps of helminth (worm) infection distributions are essential to target control strategies to those populations in greatest need. Although many surveys have been conducted in endemic countries, the data are rarely available in a form that is accessible to policy makers and the managers of public health programmes. This is especially true in sub-Saharan Africa, where empirical data are seldom in the public domain. In an attempt to address the paucity of geographical information on helminth risk, this article describes the development of an updated global atlas of human helminth infection, showing the example of East Africa. METHODS: Empirical, cross-sectional estimates of infection prevalence conducted since 1980 were identified using electronic and manual search strategies of published and unpublished sources. A number of inclusion criteria were imposed for identified information, which was extracted into a standardized database. Details of survey population, diagnostic methods, sample size and numbers infected with schistosomes and soil-transmitted helminths were recorded. A unique identifier linked each record to an electronic copy of the source document, in portable document format. An attempt was made to identify the geographical location of each record using standardized geolocation procedures and the assembled data were incorporated into a geographical information system. RESULTS: At the time of writing, over 2,748 prevalence surveys were identified through multiple search strategies. Of these, 2,612 were able to be geolocated and mapped. More than half (58%) of included surveys were from grey literature or unpublished sources, underlining the importance of reviewing in-country sources. 66% of all surveys were conducted since 2000. Comprehensive, countrywide data are available for Burundi, Rwanda and Uganda. In contrast, information for Kenya and Tanzania is typically clustered in specific regions of the country, with few records from areas with very low population density and/or environmental conditions which are unfavourable for helminth transmission. Information is presented on the prevalence and geographical distribution for the major helminth species. CONCLUSION: For all five countries, the information assembled in the current atlas provides the most reliable, up-to-date and comprehensive source of data on the distribution of common helminth infections to guide the rational implementation of control efforts

Climate change and infectious livestock diseases: The case of Rift Valley fever and tick-borne diseases

Climate change influences the occurrence and transmission of a wide range of livestock diseases through multiple pathways. Diseases caused by pathogens that spent part of their life cycle outside the host (e.g. in vectors or the environment) are more sensitive in this regard, compared to those caused by obligate pathogens. In this chapter, we use two well-studied vector-borne diseases—Rift Valley fever (RVF) and tick-borne diseases (TBDs)—as case studies to describe direct pathways through which climate change influences infectious disease-risk in East and southern Africa. The first case study demonstrates that changes in the distribution and frequency of above-normal precipitation increases the frequency of RVF epidemics. The second case study suggests that an increase in temperature would cause shifts in the spatial distribution of TBDs, with cooler and wetter areas expected to experience heightened risk with climate change. These diseases already cause severe losses in agricultural productivity, food security and socio-economic development wherever they occur, and an increase in their incidence or geographical coverage would intensify these losses. We further illustrate some of the control measures that can be used to manage these diseases and recommend that more research should be done to better understand the impacts of climate change on livestock diseases as well as on the effectiveness of the available intervention measures

Auswirkungen des Ausbaus von Bewässerungssystemen auf die Übertragung des Rift Valley-Fiebers zwischen Epidemien und Jahreszeiten im Bura Sub-County, Tana River County, Kenia

The government of Kenya has prioritized food production through revitalized and sustained agricultural expansion as a means of achieving food security for the rapidly growing population, uplifting the living standards of rural communities by providing them with livelihood opportunities as well as jumpstarting overall economic growth for employment and wealth creation through the export of excess produce and by products. Key among several policy directives issued in this regard was the harnessing of the country’s vast irrigation potential, through the expansion of existing irrigation schemes as well as establishment of new ones along the Tana and Athi river basins as well as along the shoreline of Lake Victoria. The development of these schemes however has the potential to alter local environmental and ecological conditions that may influence the risk of RVF disease transmission. Given that a thorough understanding of the risk factors precipitating the occurrence of any infectious disease is vital for its effective control, this study aimed to investigate whether these land-use changes associated with the development of irrigation schemes had any impact on the transmission dynamics of RVF virus. This study involved the spatio-temporal evaluation and comparison of the abundance, distribution and species diversity of potential vectors of RVF virus across three villages with differing ecological habitats in Bura, Tana River County, Kenya. These included the irrigated ecosystem represented by Bura irrigation scheme located near Bura township, the riverine ecosystem represented by Husingo village that is adjacent to Tana River and the dry, pastoral ecosystem represented by Chifiri village which is located further inland, away from both the irrigated and riverine ecosystems. A concurrent longitudinal study was also undertaken to measure and compare the risk of RVF on the local population of sheep and goats kept by households, and between the three ecosystems. Representative samples of mosquitoes were collected from all ecosystems and morphologically identified using taxonomic keys. The sources of blood meals were also examined in order to identify the host spectrum of engorged females while sampling of sentinel animals for RVF antibodies was undertaken as a direct measure of risk. Comparative and multivariable analysis between these ecosystems revealed that the irrigated and riverine ecosystems were similar in terms of mosquito abundance and seasonality, despite one being naturally occurring while the other being man-made. Further, the irrigated ecosystem maintained a constant and minimum presence of mosquitoes throughout all seasons, while the riverine ecosystem exhibited much more sensitivity to rainfall, with mosquito abundance significantly increasing during the wet season. The host spectrum of blood fed females revealed that most blood meals came from easily available and accessible hosts such as goats, sheep and humans. Screening of sheep and goats for RVFV antibodies detected several seroconversions in the riverine and irrigated ecosystem, with those within the riverine ecosystem all occurring in one month approximately eight weeks after the start of the rainy season while those within the irrigated ecosystem were spread out over several months thereafter. The seroconversion study, which was a direct measure of RVF disease risk, indicated that most seroconversions occurred during the rainy season within the riverine ecosystem, while those within the irrigated ecosystem were spread out over several months. No seroconversions were detected in the much drier pastoralist ecosystem. The findings of this study suggest that further expansion of the irrigation scheme or establishment of new ones in this region will lead to a gross increase in the abundance and diversity of total mosquitoes, as well as potential vectors of RVF virus. The results further imply that with increased numbers of vectors, in the presence of low numbers of animal hosts may pose an increased risk of spillover infection to humans as opportunistic hosts during large epidemics. In addition to irrigation expansion, rainfall and flooding still remains a significant risk factor for the transmission of RVF virus in this county, especially in the non-irrigated riverine and pastoral ecosystems, and particularly in the presence of large numbers of naïve animal hosts. Practical implications of these findings include targeted vector surveillance especially of known vectors of RVF virus as well as the formulation and implementation of integrated vector and environmental control programs. Vector competence studies of other mosquito species identified that might be potential vectors are recommended in future in order to improve on current outbreak prediction models as well as evaluate the success of potential surveillance and control options.Die kenianische Regierung hat die Lebensmittelproduktion zur Priorität gemacht, um die Versorgung mit Lebensmitteln für eine schnell wachsende Bevölkerung sicherzustellen. Dies erfolgte vor allem durch anhaltende Expansion landschaftlicher Nutzflächen in zuvor naturbelassenen Gebieten. Dadurch erhöhte sich der Lebensstandard ländlicher Gebiete, weil sich neue Erwerbsmöglichkeiten bildeten, was die positive wirtschaftliche Entwicklung dieser Gebiete förderte, dabei insbesondere den Export landwirtschaftlicher Produkte. Ein Schlüsselfaktor dieser Politik war die umfassende Planung neuer aber auch der Ausbau bestehender Bewässerungssysteme entlang der Flussläufe des Tana und Athi, sowie des Ufers des Viktoriasees, um diese fruchtbaren Trockengebiete landwirtschaftlich nutzen zu können. Diese Entwicklung hat das Potential, das Ökosystem so zu verändern, dass es das Übertragungsrisiko des Rift-Valley-Fieber-Virus (RVFV) beeinflusst. Diese Studie hatte die Untersuchung der Einflüsse solcher Bewässerungssysteme auf die Übertragungsmechanismen des RVFV zum Ziel. Denn die intensive Auswertung aller bekannter Risikofaktoren einer Infektionskrankheit ist die Grundlage zur Entwicklung effizienter undwirksamer Bekämpfungsstrategien. Diese Studie umfasst eine geographische und zeitliche Auswertung der Fangzahlen, Verbreitung und Diversität potenzieller Vektoren des RVFV in drei Dörfern mit unterschiedlichem Habitat in der Gemeinde Bura, Tana River, Kenia. Hierbei repräsentieren Bura Township und Umgebung eine durch Bewässerungssysteme geprägte Landschaft, während sich das Dorf Husingo durch die natürlichen Nebengewässer des Flusses Tana auszeichnet. Das Dorf Chifiri ist Vertreter eines trockenen, pastoral geprägten Ökosystems. Parallel dazu wurde eine vergleichende Langzeitstudie zur Ermittlung des RVF-Risikos für die Bevölkerung und ihrer Ziegen und Schafe unter Berücksichtigung der Unterschiede zwischen den drei Gemeinden durchgeführt. Repräsentative Proben von Stechmücken wurden aus allen Ökosystemen gefangen und mit taxonomischen Schlüsseln morphologisch bestimmt. Außerdem wurden die Blutmahlzeiten der Mücken untersucht, um das Wirtsspektrum vollgesogener Weibchen zu ermitteln, während das Beproben von Sentinel-Tieren auf RVFV-Antikörper als direkter Indikator für das Übertragungsrisiko durchgeführt wurde. Vergleichende und multivariable Statistikanalysen ergaben, dass die künstlich bewässerten und natürlichen Fluss-Ökosysteme sich in Mückenvorkommen und Saisonalität ähnelten. Allerdings zeigte das künstlich bewässerte Ökosystem ein konstantes, wenn auch minimales, Vorkommen von Stechmücken, das nicht mit Jahreszeitenwechseln korrelierte. Das natürliche Flussökosystem hingegen zeichnete eine bedeutende Zunahme der Mückenmenge während der Regenzeit aus. Das Wirtsspektrum der vollgesogenen Weibchen ergab, dass die meisten Blutmahlzeiten von leicht zugänglichen Wirten wie Ziegen, Schafen und Menschen stammten. Bei der Untersuchung von Schafen und Ziegen auf RVFV-Antikörper wurden mehrere Serokonversionen sowohl im künstlich sowie auch natürlich bewässerten Ökosystem festgestellt. Die Serokonversionsstudie, die ein direktes Maß für das RVF-Übertragungsrisiko darstellte, zeigte, dass die meisten Serokonversionen während der Regenzeit im Gebiet des natürlichen Fluss-Ökosystems auftraten, während die des künstlich bewässerten Ökosystems über mehrere Monate verteilt waren. Im trockenen, pastoralen Ökosystem wurden keine Serokonversionen festgestellt. Die Ergebnisse dieser Studie deuten darauf hin, dass ein Ausbau bestehender Bewässerungssysteme und auch die Einrichtung neuer Systeme, zu einer generellen Zunahme der Stechmückenzahlen, sowie einer erhöhten Artenvielfalt der Mücken führen kann, einschließlich potenzieller Vektoren des RVFV. Die Ergebnisse legen die Vermutung nahe, dass diese Vektoren, bei weniger werdenden oder gänzlich fehlenden tierischer Wirten, zunehmend Menschen als opportunistische Wirte wählen könnten, was RVFV-Infektionen im Menschen begünstigen würde. Neben der Expansion von Bewässerungssystemen sind Regenfälle und Überschwemmungen nach wie vor ein wichtiger Risikofaktor für die Übertragung des RVFV in diesem Landkreis. Insbesondere in den natürlich bewässerten Flussökosystemen, aber auch in pastoralen Ökosystemen, vor allem in Gegenwart einer großen Anzahl immunologisch naiver Wirte. Praktische Anwendung dieser Erkenntnisse wären eine routinemäßige Überwachung des Vorkommens und Infektionsstatus bekannter RVFV-Vektoren, sowie die Formulierung und Implementierung integrierter Vektor- und Umweltkontrollprogramme. Vektorkompetenzstudien anderer identifizierter Mückenarten, die potenzielle Vektoren sein könnten, werden empfohlen, um aktuelle Vorhersagemodelle für Ausbrüche in der Zukunft zu verbessern und den Erfolg potenzieller Überwachungs- und Kontrolloptionen zu bewerten

Rift Valley fever/malaria study site analysis and major findings for Rift Valley fever and malaria transmission

This deliverable gives provisional results of the on-going analyses on RVF and malaria transmission studies in Kenya. Analyses on RVF are based on historical data on RVF outbreaks recorded in the study site between 1961 and 2007, initial outputs from the RVF dynamical model that is being developed, and data collected from participatory studies. All the analyses on malaria are based on hospital records covering the period 2006 – 2011

A multiplex fluorescence microsphere immunoassay for increased understanding of Rift Valley fever immune responses in ruminants in Kenya

Rift Valley fever virus (RVFV) is an important mosquito-borne pathogen with devastating impacts on agriculture and public health. With outbreaks being reported beyond the continent of Africa to the Middle East, there is great concern that RVFV will continue to spread to non-endemic areas such as the Americas and Europe. There is a need for safe and high throughput serological assays for rapid detection of RVFV during outbreaks and for surveillance. We evaluated a multiplexing fluorescence microsphere immunoassay (FMIA) for the detection of IgG and IgM antibodies in ruminant sera against the RVFV nucleocapsid Np, glycoprotein Gn, and non-structural protein NSs. Sheep and cattle sera from a region in Kenya with previous outbreaks were tested by FMIA and two commercially available competitive ELISAs (BDSL and IDvet). Our results revealed strong detection of RVFV antibodies against the Np, Gn and NSs antigen targets. Additionally, testing of samples with FMIA Np and Gn had 100% agreement with the IDvet ELISA. The targets developed in the FMIA assay provided a basis for a larger ruminant disease panel that can simultaneously screen several abortive and zoonotic pathogens