Reflections on IDEAL: What we have learnt from a unique calf cohort study.

The year 2020 marks a decade since the final visit was made in the 'Infectious Diseases of East African Livestock' (IDEAL) project. However, data generation from samples obtained during this ambitious longitudinal study still continues. As the project launches its extensive open-access database and biobank to the scientific community, we reflect on the challenges overcome, the knowledge gained, and the advantages of such a project. We discuss the legacy of the IDEAL project and how it continues to generate evidence since being adopted by the Centre for Tropical Livestock Genetics and Health (CTLGH). We also examine the impact of the IDEAL project, from the authors perspective, for each of the stakeholders (the animal, the farmer, the consumer, the policy maker, the funding body, and the researcher and their institution) involved in the project and provide recommendations for future researchers who are interested in running longitudinal field studies.

Seroprevalence of respiratory viral pathogens of indigenous calves in Western Kenya.

Most studies of infectious diseases in East African cattle have concentrated on gastro-intestinal parasites and vector-borne diseases. As a result, relatively little is known about viral diseases, except for those that are clinically symptomatic or which affect international trade such as foot and mouth disease, bluetongue and epizootic haemorrhagic disease. Here, we investigate the seroprevalence, distribution and relationship between the viruses involved in respiratory disease, infectious bovine rhinotracheitis virus (IBR), bovine parainfluenza virus Type 3 (PIV3) and bovine viral diarrhoea virus (BVDV) in East African Shorthorn Zebu calves. These viruses contribute to the bovine respiratory disease complex (BRD) which is responsible for major economic losses in cattle from intensive farming systems as a result of pneumonia. We found that calves experience similar risks of infection for IBR, PIV3, and BVDV with a seroprevalence of 20.9%, 20.1% and 19.8% respectively. We confirm that positive associations exist between IBR, PIV3 and BVDV; being seropositive for any one of these three viruses means that an individual is more likely to be seropositive for the other two viruses than expected by chance.

Variation and covariation in strongyle infection in East African shorthorn zebu calves.

Parasite burden varies widely between individuals within a population, and can covary with multiple aspects of individual phenotype. Here we investigate the sources of variation in faecal strongyle eggs counts, and its association with body weight and a suite of haematological measures, in a cohort of indigenous zebu calves in Western Kenya, using relatedness matrices reconstructed from single nucleotide polymorphism (SNP) genotypes. Strongyle egg count was heritable (h(2) = 23.9%, s.e. = 11.8%) and we also found heritability of white blood cell counts (WBC) (h(2) = 27.6%, s.e. = 10.6%). All the traits investigated showed negative phenotypic covariances with strongyle egg count throughout the first year: high worm counts were associated with low values of WBC, red blood cell count, total serum protein and absolute eosinophil count. Furthermore, calf body weight at 1 week old was a significant predictor of strongyle EPG at 16-51 weeks, with smaller calves having a higher strongyle egg count later in life. Our results indicate a genetic basis to strongyle EPG in this population, and also reveal consistently strong negative associations between strongyle infection and other important aspects of the multivariate phenotype.

A longitudinal assessment of the serological response to Theileria parva and other tick-borne parasites from birth to one year in a cohort of indigenous calves in western Kenya.

Tick-borne diseases are a major impediment to improved productivity of livestock in sub-Saharan Africa. Improved control of these diseases would be assisted by detailed epidemiological data. Here we used longitudinal, serological data to determine the patterns of exposure to Theileria parva, Theileria mutans, Babesia bigemina and Anaplasma marginale from 548 indigenous calves in western Kenya. The percentage of calves seropositive for the first three parasites declined from initial high levels due to maternal antibody until week 16, after which the percentage increased until the end of the study. In contrast, the percentage of calves seropositive for T. mutans increased from week 6 and reached a maximal level at week 16. Overall 423 (77%) calves seroconverted to T. parva, 451 (82%) to T. mutans, 195 (36%) to B. bigemina and 275 (50%) to A. marginale. Theileria parva antibody levels were sustained following infection, in contrast to those of the other three haemoparasites. Three times as many calves seroconverted to T. mutans before seroconverting to T. parva. No T. parva antibody response was detected in 25 calves that died of T. parva infection, suggesting that most deaths due to T. parva are the result of acute disease from primary exposure.

Hematological profile of East African short-horn zebu calves from birth to 51 weeks of age.

This paper is the first attempt to accurately describe the hematological parameters for any African breed of cattle, by capturing the changes in these parameters over the first 12 months of an animal's life using a population-based sample of calves reared under field conditions and natural disease challenge. Using a longitudinal study design, a stratified clustered random sample of newborn calves was recruited into the IDEAL study and monitored at 5-weekly intervals until 51 weeks of age. The blood cell analysis performed at each visit included: packed cell volume; red cell count; red cell distribution width; mean corpuscular volume; mean corpuscular hemoglobin concentration; hemoglobin concentration; white cell count; absolute lymphocyte, eosinophil, monocyte, and neutrophil counts; platelet count; mean platelet volume; and total serum protein. The most significant age-related change in the red cell parameters was a rise in red cell count and hemoglobin concentration during the neonatal period. This is in contrast to what is reported for other ruminants, including European cattle breeds where the neonatal period is marked by a fall in the red cell parameters. There is a need to establish breed-specific reference ranges for blood parameters for indigenous cattle breeds. The possible role of the postnatal rise in the red cell parameters in the adaptability to environmental constraints and innate disease resistance warrants further research into the dynamics of blood cell parameters of these breeds.

The dental health of 12-year-old children whose diets include canned fruit from local factories: an added risk for caries?

OBJECTIVE: To determine the dental health of 12-year-old children from households that are supplied with sweetened canned fruit from local factories. METHODS: The DMFS and DMFT indices were determined for 12-year-old pupils from 6 schools, 3 of which are situated in communities with fruit canning factories. Subjects were questioned about the workplace of household members and supplies of sweetened canned fruit from factories. To compare indices we used a two-way analysis of variance, for multiple comparisons the Bonferroni Test and for proportions the Chi-Squared Test. Fluoride content of the drinking water was measured for each school. RESULTS: The fluoride content for all schools was less than 0.1 ppm. In only 2 schools were the majority of pupils from households that were supplied regularly with canned fruit from factories. An analysis of the DMFT data of the children in all the schools showed that there were significantly fewer children with a DMFT = 0 and significantly more with a DMFT = 4+ in the 2 schools. The mean DMFS and DMFT of children in households supplied with canned fruit were significantly higher than those children without the supply. CONCLUSION: The supply of sweetened canned fruit to households may be an added risk to dental health for the children in that household.