Geographic distribution of non-clinical Theileria parva infection among indigenous cattle populations in contrasting agro-ecological zones of Uganda: implications for control strategies.

Fredrick Kabi,Charles Masembe,Halid Kirunda,Riccardo Negrini,Vincent Muwanika

doi:10.1186/1756-3305-7-414

Abstract

BackgroundNon-clinical Theileria parva infection among indigenous cattle occurs upon recovery from primary disease during the first year of life. Continuous exposure to infection through contaminated tick infestations with absence of clinical disease gives rise to endemic stability. Endemic stable populations may become sources of infection if contaminated tick vectors are shared with susceptible exotic cattle. This study aimed at establishing a nationwide distribution of non-clinical T. parva infection among indigenous cattle populations to inform novel control strategies.MethodsThe occurrence of non-clinical T. parva infection among apparently healthy 925 indigenous cattle from 209 herds spread out in 10 agro-ecological zones (AEZs) was determined using a nested PCR assay. The influence of AEZ, breed, sex, age and farmers’ ranking of ECF importance were interrogated for influence of non-clinical parasite occurrence.ResultsThe overall prevalence of non-clinical T. parva infection was 30% (278/925). A gradual increase of non-clinical T. parva infection was observed ranging from 17% (95% CI: 0.03 – 0.23) to 43% (95% CI: 0.3 – 0.55) in the North Eastern Savannah Grasslands (NESG) to the Western Highland Ranges (WHR) respectively. A similarly associated 18% (95% CI: 0.07 – 0.28) and 35% (95% CI: 0.3 – 0.39) non-clinical parasite prevalence was observed among the East African shorthorn Zebu (EASZ) and Ankole cattle respectively. Average herd level non-clinical T. parva prevalence was 28%, ranging from zero to 100%. The likelihood of non-clinical T. parva infection was 35.5% greater in the western highlands compared to the northeastern semi-arid AEZs.ConclusionsNon-clinical T. parva occurs countrywide, structured along patterns of AEZ and breed gradients. These findings may guide policy formulation, deployment of integrated control strategies and local cattle improvement programs.

Highlights

Non-clinical Theileria parva infection among indigenous cattle occurs upon recovery from primary disease during the first year of life
Endemic stability is a state of interaction between the host, tick vector and pathogen, whereby calves are infested with contaminated ticks, exhibit non-acute or mild clinical disease, which further develops into a high level of immunity in adult cattle with absence of clinical disease as described by Jonsson et al [2]
The medium non-clinical T. parva infection prevalence zones were composed of KP, NWSG, PSG and WSG i.e., 22%, 25%, 25% 26% and LVC 27% (0.15 0.38) respectively

Summary

Introduction

Non-clinical Theileria parva infection among indigenous cattle occurs upon recovery from primary disease during the first year of life. East coast fever (ECF) is caused by T. parva and often exhibits a non-clinical infection among indigenous cattle which have recovered from the primary disease and are continuously exposed to infection, a phenomenon called endemic stability. In Uganda, indigenous cattle breeds comprise about 93.3% of the national cattle herd and include the Ankole, East African shorthorn zebu (EASZ), Nganda and their crosses [3]. Their ability to survive under continuous ECF challenge is known to have developed as a result of host parasite evolutionary co-existence dating back to cattle introduction in the disease endemic region [4,5]. More so where indigenous and exotic cattle are managed in close proximity, resulting into sharing of contaminated ticks, risks of disease transmission and high mortalities [5] among the later

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