Epidemiology of East Coast Fever in smallholder livestock systems of East Africa

Abstract

The health and productivity of livestock are pivotal in rural livelihoods across sub-Saharan Africa, providing nutrition, income and employment. However, infectious diseases, particularly those caused by haemopathogens, pose a significant threat to their health and productivity. Haemopathogens including Theileria parva, Anaplasma marginale, Ehrlichia ruminatium, and Babesia spp. infect the host’s bloodstream, causing signs like fever, anaemia, organ dysfunction and death. East Coast fever (ECF), caused by T. parva and transmitted by the tick Rhipicephalus appendiculatus, is among the deadliest of these infections and causes the development of lymphoproliferative syndrome and the significant reduction in milk production, fertility and growth. Co-infections are common in endemic regions with cattle often harbouring multiple pathogens concurrently which may result in either synergistic or antagonistic effects on disease progression. Co-infections can result in altered immune responses, misdiagnosis, and reduced treatment efficacy. Certain co-infections, specifically other Theileria species may offer protective effects when a calf contracts ECF. Recent research has identified potential heritable genetic tolerance to ECF, particularly involving a variant in the FAF1B gene which regulates immune-mediated apoptosis.

This study aims to investigate the epidemiology, transmission, co-infection dynamics, and inherited tolerance of haemopathogen diseases in East African smallholder cattle systems, with a specific focus on ECF. Data from the 2007–2009 Infectious Diseases of East African Livestock (IDEAL) study, including novel Illumina MiSeq pathogen profiles, from a haemobiome tool developed by the University of Edinburgh, Centre for Tropical Livestock Genetics and Health (CTLGH) and cattle genetic data, were used to conduct statistical analyses. Results were used to assess the influencers and predictors of calf survival and disease outcome.

Calves homozygous for the FAF1B (FAS-associated factor 1) T allele (TT) exhibited a reduced risk in mortality attributed to ECF, supporting a potential role of genetically mediated tolerance. Additionally, prior exposure to less pathogenic Theileria species (Theileria-mutans and/or Therileria-velifera) before infection with T. parva was statistically associated with a higher chance of survival, implying that this co-infection plays a protective role. The findings aid in informing effective disease management strategies, including selective breeding for tolerant genotypes and harnessing the potential of co-infections to mitigate disease severity ultimately contributing to reduced cattle mortality and greater economic resilience for smallholder farmers.