The role of heartwater (Ehrlichia ruminantium infection) and other tick-borne pathogens in Acute Camel Death Syndrome in Kenya

Dromedary camels are important food-producing animals in northern Kenya and vital for the economy, food security and well-being of pastoralist communities. Their population is steadily increasing year-on-year and stood at over 3.2 million in 2016. The Kenyan camel meat and milk industry is worth approximately US$11 million annually. Acute Camel Death Syndrome (ACDS) is an emerging disease of unknown cause affecting camel herds in parts of northern Kenya. Up to 100% of affected adult camels can die without treatment. Unlike other camel diseases that are well-recognised by local pastoralists, ACDS is a new disease for which Kenyan camel keepers have no vernacular name. Clinical and post-mortem signs show strong similarities to heartwater, a tick-borne disease of sheep, goats and cattle that is endemic throughout sub-Saharan Africa, but has only been described in camels in other parts of Africa on three occasions in the past 60 years. Affected camel herds may be heavily infested with ticks, and the causative agent of heartwater, the intracellular bacterium Ehrlichia ruminantium, has been detected in ticks removed from camels affected by ACDS. However this does not prove that ACDS is a manifestation of heartwater in camels; other tick-borne pathogens (TBP) may be involved in the syndrome.

It is essential to identify the causative agent of ACDS so that effective preventive and/or control measures can be implemented.

To investigate the role of heartwater and other TPB in ACDS, we propose to carry out a broad-spectrum survey of camels, sheep that graze alongside them, and ticks infesting both species, in areas where ACDS outbreaks have occurred. As controls, we will similarly sample camels, sheep and ticks in areas where ACDS has not been reported. We will interview camel keepers to determine their prior knowledge of ACDS and how it is distinct from other camel diseases with which they are familiar, and to establish disease incidence, symptoms, post mortem signs and concurrent levels of tick infestation that they have observed during outbreaks. We will collect blood and serum samples and ticks from camels and co-grazing sheep; blood samples will be screened for presence of E. ruminantium and other TBP indicating current infection and serum samples will be tested for antibodies to E. ruminantium and other TBP indicating previous exposure. Ticks will be screened for infection with E. ruminantium and other TBP to determine the range of pathogens circulating in the sample areas. We will attempt to isolate strains of the different pathogens by culturing them in bovine and tick cell lines; gene sequences of isolated novel strains will be compared with those of known strains from other hosts to look for differences that might explain the emergence of ACDS as a new camel disease.

If there is an outbreak of ACDS in any of our study areas during the project, we will collect clinical and post-mortem samples from affected camels and process them in the same way as the survey samples. We will bank aliquots of the camel and tick samples in cryostorage, thereby creating a resource for use in future studies on ACDS and by scientists researching other factors affecting camel health.

An important element of our project will be capacity-building relating to ACDS and more generally to camel health in Kenya. Using the knowledge gained from our field and laboratory studies, we will formulate protocols for diagnosis, treatment and control of ACDS, including hands-on training in appropriate sampling techniques and proper storage and transport of samples to the laboratory. In addition, we will provide the opportunity and support for a Kenyan MSc student to carry out their research project focussing on a particular aspect of our proposed study.

As well as the academic beneficiaries outlined in the previous section, the following non-academic groups will benefit from the proposed research on ACDS and other tick-borne diseases affecting camels in Kenya and other African countries:

- Reduction in mortality and morbidity of camels due to ACDS and other tick-borne pathogens will improve the nutritional and economic status of pastoralist camel keepers and their families through increased availability of milk and meat, and decreased expenditure on non-targeted or ineffective drug treatment for sick animals. Camels are a very important component of the pastoralist livestock economy in northern Kenya, and they and their owners are very vulnerable to losses. In the past, epidemics of animal disease have led to famine, and so camel health is the essence of Food Security in the region. Northern Kenya borders Somalia, with the world's highest population of dromedary camels, and an economy that is almost entirely dependent on live animal exports (~60-80% of GDP) to the Middle East. ACDS and other tick-borne diseases of camels are most likely to be present there and in other countries in the region, and also threaten their economies.

- Smallholder pastoralists in Northern Kenya will be better informed and more empowered on ACDS disease identification, factors contributing to its spread and its management and control strategies. In the long-term, when the disease is clearly understood and control strategies implemented, the farmers will realise increased camel production, leading to enhanced food security due to more milk and meat and ultimately increased incomes and better lives.

- Directorates of Veterinary and Animal Heath Services in the National and County governments in Kenya and their counterparts in other camel-keeping countries in Africa will have a better understanding of the role of ticks and tick-borne pathogens in camel health and thus be able to more appropriately target scarce resources towards diagnosis, treatment and control of camel diseases.