Epidemiology of vector-borne diseases in cattle from SE Uganda

Abstract

Vector-borne diseases, (VBD), are amongst the most important constraints to animal production in tropical and sub-tropical regions of the world, including sub-Saharan Africa, (SSA). Losses due to these diseases are estimated to be up to 25% of the region's annual livestock production total. Some of the diseases are also zoonotic and therefore contribute to human health problems. The most important VBD are caused by the protozoa: Anaplasma, Cowdria, Babesia, Theileria and Trypanosoma parasites. Anaplasma, Cowdria, Babesia and Theileria are transmitted by ticks while trypanosomes are transmitted by tsetse flies in humans and animals in Africa. Control of these diseases in SSA is non-sustainable, mainly because of ineffective disease surveillance, poor diagnostic capacity and inadequate control measures largely due to economic constraints ofthe affected governments.

Two of the most commonly used diagnostic methods, microscopy and molecular techniques for pathogen detection and species characterization, were evaluated for their sensitivity and specificity. The results showed that the two techniques have very low diagnostic agreement in detecting all the three species of trypanosomes, (kappa values < 0.02). The sensitivity of PCR amplification in detecting trypanosomes in cattle blood was found to be 5-10 times higher than microscopy. The specificity of microscopy was found to be poor, in relation to PCR amplification as it mis-diagnosed many cases as having T. vivax while PCR showed that they were T. brucei. The study showed that Theileria species were more prevalent in Tororo than in Busia (60% vs. 38%). Molecular based methods revealed that Theileria mutans was the predominant species in cattle, at 42% prevalence while the overall prevalence of Theileria species was found to be 66% in Tororo district.

The prevalence of trypanosome species was found to be 10 times higher than previously recorded in this region. The study revealed that isometamidium chloride (Samorin) treatment of cattle did not protect the animals from infection with any of the three trypanosome species for more than three months. While Samorin treatment appeared to control trypanosomiasis in areas with low prevalence, the drug had no effect in controlling the disease in high prevalence areas. It would therefore be necessary to combine the use of drug intervention with other methods such as vector control, to reduce the prevalence, in order to realize effective control of trypanosomiasis. The results further show that Samorin treatment did not offer protection against T. brucei infections in cattle. The study also showed that treatment of cattle with diminazene aceturate (Berenil) can not be relied upon to control transmission of trypanosomes. Finally, the study revealed that the prevalence of T. brucei is higher in adult animals than in calves while the prevalence of T. congolense and T. vivax is higher in animals below 24 months.