Design and descriptive epidemiology of the Infectious Diseases of East African Livestock (IDEAL) project, a longitudinal calf cohort study in western Kenya

Abstract

BackgroundThere is a widely recognised lack of baseline epidemiological data on the dynamics and impacts of infectious cattle diseases in east Africa. The Infectious Diseases of East African Livestock (IDEAL) project is an epidemiological study of cattle health in western Kenya with the aim of providing baseline epidemiological data, investigating the impact of different infections on key responses such as growth, mortality and morbidity, the additive and/or multiplicative effects of co-infections, and the influence of management and genetic factors.A longitudinal cohort study of newborn calves was conducted in western Kenya between 2007-2009. Calves were randomly selected from all those reported in a 2 stage clustered sampling strategy. Calves were recruited between 3 and 7 days old. A team of veterinarians and animal health assistants carried out 5-weekly, clinical and postmortem visits. Blood and tissue samples were collected in association with all visits and screened using a range of laboratory based diagnostic methods for over 100 different pathogens or infectious exposures.ResultsThe study followed the 548 calves over the first 51 weeks of life or until death and when they were reported clinically ill. The cohort experienced a high all cause mortality rate of 16% with at least 13% of these due to infectious diseases. Only 307 (6%) of routine visits were classified as clinical episodes, with a further 216 reported by farmers. 54% of calves reached one year without a reported clinical episode. Mortality was mainly to east coast fever, haemonchosis, and heartwater. Over 50 pathogens were detected in this population with exposure to a further 6 viruses and bacteria.ConclusionThe IDEAL study has demonstrated that it is possible to mount population based longitudinal animal studies. The results quantify for the first time in an animal population the high diversity of pathogens a population may have to deal with and the levels of co-infections with key pathogens such as Theileria parva. This study highlights the need to develop new systems based approaches to study pathogens in their natural settings to understand the impacts of co-infections on clinical outcomes and to develop new evidence based interventions that are relevant.

The epidemiology of tick-borne haemoparasites as determined by the reverse line blot hybridization assay in an intensively studied cohort of calves in western Kenya

“…The IDEAL project has been described in detail elsewhere ( Bronsvoort et al, 2013 ). In brief, a cohort of 548 East African shorthorn calves was recruited into the project at birth and monitored for a period of one year.…”

“…The aim of the study reported here was to gain further information on the prevalence of tick-borne parasites in an important farming system in eastern Africa through the use of the RLB assay. The samples were obtained from an intensively studied birth cohort of 548 calves in western Kenya ( Bronsvoort et al, 2013 ). Apart from baseline prevalence, the results were used to determine the levels of coinfections in the calf population.…”

Signatures of positive selection in East African Shorthorn Zebu: A genome-wide single nucleotide polymorphism analysis

“…They would be expected to display some level of tolerance – resistance to pathogens common in East Africa, e.g. Anaplasma marginale , Babesia bigemina , Haemonchus placei and Theileria parva 9 10 11 . However, a recent study has shown that in the absence of any veterinary intervention, 16% of newborn calves still died from natural causes during their first year 10 .…”

“…Anaplasma marginale , Babesia bigemina , Haemonchus placei and Theileria parva 9 10 11 . However, a recent study has shown that in the absence of any veterinary intervention, 16% of newborn calves still died from natural causes during their first year 10 . Specifically, East Coast Fever and haemonchosis have been identified as the main causes of death 11 .…”

Polymorphisms of BoLA-DRB 3.2 gene and associated genetic relationships among four strains of Tanzania shorthorn zebu cattle

“…taurus (Hansen, 2004;Maule, 1990;Mattioli et al, 2000;Porter, 1991). A few examples include the West African N'Dama cattle which have been confirmed to be tolerant to trypanosomiasis (Kim et al,2017) and the Kenyan Small East African zebu (SEAZ) which were shown to be resistant to Rhipicephalus (R.) appendiculatus ticks (Latif & Pegram, 1992) and to survive well in environments with poor quality forage, water scarcity and high temperatures (Western & Finch, 1986;de Clare Bronsvoort et al,2013). Tanzania shorthorn zebu (TSZ) is the breed name for the indigenous cattle of Tanzania and 12 strains have been identified.…”