Tick-borne diseases affecting cattle in Kenya

Summary

Tick-borne pathogens cause disease in both animals and humans. This necessitates the need for developing diagnostic kits that are customised for tick-borne pathogens found in Kenya to improve surveillance, stay ahead of emerging variants and to implement appropriate preventive measures before human outbreaks occur.

Background

Tick-borne pathogens (TBPs) cause colossal losses to livestock production, in addition to the zoonotic disease threat to animal owners and handlers. Currently the diagnostic capacity of these pathogens, especially in developing countries such as Kenya, is inadequate hence underreporting. This has resulted in low prioritization during resource allocation and policymaking. Moreover, the diversity and epidemiology of these TBPs are constantly changing due to the effects of climate change,  increasing human population, and constantly evolving land-use patterns in Kenya, especially in urban and peri-urban areas. This has been evident by a decrease in the prevalence of the previously endemic tick-borne diseases in Kenya, such as East Coast Fever and babesiosis, and the corresponding increase in ehrlichiosis cases previously less widespread. Cattle are considered the domestic reservoir for some of the tick-borne pathogens that are most threatening to public health. This study utilised molecular techniques to analyse blood and ticks found attached to the cattle to determine which tick-borne pathogens may be emerging in the peri-urban areas of Nairobi City County.

Description of the study

This was an epidemiological and molecular study to determine tick-borne pathogens in the Anaplasma and Ehrlichia genera that infect cattle from smallholder dairy farms in peri-urban Nairobi. Dairy farming in Nairobi's peri-urban areas is characterized by small land sizes resulting from the growing urban population which has led to continued land sub-division. Consequently, farmers live near their livestock, and young stock is kept inside people’s houses. These minimal land spaces for dairy production have led to sub-optimal animal husbandry practices that compromise on animal welfare and subsequently their immunity and increase susceptibility to diseases, including emerging pathogens. 

This research project was motivated by the ambiguousness of diagnoses using both microscopy and serology: the former can fail to differentiate between the Anaplasma and Ehrlichia genera, and the latter has low sensitivity and suffers cross-reactivity across pathogen species. Therefore, despite microscopy and serology being readily available and cheap techniques for diagnosing tick-borne diseases in resource-poor regions, confirmatory molecular-based techniques are necessary to clarify rising cases being diagnosed as ehrlichiosis and detect any emerging pathogens.

 This study was conducted in peri-urban areas of Nairobi City County, Kenya. These are the geographical areas on the outskirts of Nairobi City surrounding the central business district (CBD). For data collection purposes, the county was subdivided into four quadrants, and for each quadrant, the sub-county with the highest cattle population was designated as the study population. Random sampling was used to recruit farms and animals, a total of 306 dairy cattle in 109 smallholder farms in the study population. Cattle whole blood and ticks infesting the cattle were collected for analysis of Anaplasma and Ehrlichia pathogens.

Outcome of the Study

Out of the cattle sampled, 19.9% (61/306) and 3.3% (10/306) were positive for Anaplasma and Ehrlichia pathogens, respectively, using Polymerase Chain Reaction (PCR). All the Ehrlichia positive samples and twenty-nine randomly selected Anaplasma positive were sequenced for confirmation of the pathogen species. Of these, 44.8% (13/29) and 40% (4/10) of the isolates were confirmed as emerging Anaplasma platys and Ehrlichia minasensis, respectively. These were the first reports of these pathogens in cattle in Kenya. Anaplasma platys has a zoonotic potential and causes human disease characterised by headaches, intermittent edema and muscle pain. Transmission from cattle to humans is through tick bites, and a range of tick species were also found to be infesting the study cattle. The ticks were found to harbour various Anaplasma and Ehrlichia pathogens, including zoonotic Rickettsia conorii and R. aeschlimanii. Rickettsia conorii is the causative agent for Mediterranean Spotted Fever (MSP) in humans. These rickettsioses commonly present with fever and may be confused with malaria or typhoid, especially in areas where these diseases are endemic. This results in misdiagnosis and underreporting.

 These findings indicate the emergence of novel Anaplasma, Ehrlichia, and Rickettsia pathogens, some of which are of public health importance, highlighting the urgent need for effective control of the vector ticks to prevent infection of cattle, which are the domestic reservoirs for human disease. It is imperative that veterinarians and physicians include these pathogens in their differential diagnoses to enable early and correct diagnosis and treatment. Additionally, creating awareness of the potential for human infection from infected cattle and ticks encourages owners and handlers to exercise caution during their routine activities and also to seek medical attention in the event of exposure to tick-bites. 

Lessons 

This research demonstrates that complex health issues require multidisciplinary involvement. It also suggests that further research to investigate the household members from which the infected cattle come would be important to determine if such cattle were infected with similar pathogens. The public health implications of these findings also indicate that policymakers must be involved at project inception to ensure circulation of new information and to facilitate adoption of strategies that can improve public health.

Impact

These findings are important because they inform the development of diagnostic kits that are customised for pathogens based on the Kenyan isolate sequences from this study. Commercial kits currently in use are from pathogen isolates from other regions of the world, which may differ from the ones in Kenya. Pathogens must be surveilled continuously and diligently to stay ahead of emerging variants and to implement appropriate preventive measures before human outbreaks occur. In our study, the willingness of cattle owners to modify their behaviour based on this new information was observed immediately. Such measures include avoidance of tick-bites, which is the mode of transmission of the pathogens. A policy brief to guide effective prevention and control strategies is under development for the Zoonotic Diseases Unit, Kenya (ZDU) and the Director of Veterinary Services.  Bridging knowledge gaps around emerging tick-borne pathogens requires a one-health approach involving public health experts, veterinarians, medical practitioners, environmentalists, molecular biologists, livestock owners, farmers and communities. 

About Getrude Shepelo

Getrude Shepelo is a Kenyan veterinarian and a lecturer at the Department of Clinical Studies, Faculty of Veterinary Medicine, University of Nairobi, Kenya. She is a Consortium for Advanced Research Training in Africa (CARTA) Graduate, from which she received funding for her PhD work and mentorship. CARTA is one of the eleven Developing Excellence, Leadership and Training in Science in Africa (DELTAS Africa) programmes. DELTAS Africa funds Africa-based scientists to amplify the development of world-class research and scientific leadership on the continent while strengthening African institutions. It is implemented through the Alliance for Accelerating Excellence in Science in Africa (AESA) platform, a funding, agenda-setting, programme management initiative founded by the African Academy of Sciences (AAS), the African Union Development Agency (AUDA-NEPAD), founding and funding global partners, and through a resolution of the summit of African Union Heads of Governments. DELTAS Africa is supported by Wellcome and the United Kingdom Foreign, Commonwealth and Development Office (FCDO, formerly DFID).