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Corridor disease (CD) is a fatal condition of cattle caused by buffalo-derived Theileria parva. Unlike the related condition, East Coast fever, which results from infection with cattle-derived T. parva, CD has not been extensively studied. We describe in detail the clinical and laboratory findings in cattle naturally infected with buffalo-derived T. parva. Forty-six cattle were exposed to buffalo-derived T. parva under field conditions at the Ol Pejeta Conservancy, Kenya, between 2013 and 2018. The first signs of disease observed in all animals were nasal discharge (mean day of onset was 9 days post-exposure), enlarged lymph nodes (10 days post-exposure), and pyrexia (13.7 days post-exposure). Coughing and labored breathing were observed in more than 50% of animals (14 days post-exposure). Less commonly observed signs, corneal edema (22%) and diarrhea (11%), were observed later in the disease progression (19 days post-exposure). All infections were considered clinically severe, and 42 animals succumbed to infection. The mean time to death across all studies was 18.4 days. The mean time from onset of clinical signs to death was 9 days and from pyrexia to death was 4.8 days, indicating a relatively short duration of clinical illness. There were significant relationships between days to death and the days to first temperature (chi2 = 4.00, p = 0.046), and days to peak temperature (chi2 = 25.81, p = 0.001), animals with earlier onset pyrexia died sooner. These clinical indicators may be useful for assessing the severity of disease in the future. All infections were confirmed by the presence of macroschizonts in lymph node biopsies (mean time to parasitosis was 11 days). Piroplasms were detected in the blood of two animals (4%) and 20 (43%) animals seroconverted. In this study, we demonstrate the successful approach to an experimental field study for CD in cattle. We also describe the clinical progression of CD in naturally infected cattle, including the onset and severity of clinical signs and pathology. Laboratory diagnoses based on examination of blood samples are unreliable, and alternatives may not be available to cattle keepers. The rapid development of CD requires recognition of the clinical signs, which may be useful for early diagnosis of the disease and effective intervention for affected animals.

Integrative management of wildlife and livestock requires a clear understanding of the diseases transmitted between the two populations. The tick-borne protozoan parasite Theileria parva causes two distinct diseases in cattle, East Coast fever and Corridor disease, following infection with parasites derived from cattle or buffalo, respectively. In this study, cattle were immunized with a live sporozoite vaccine containing three T. parva isolates (the Muguga cocktail), which has been used extensively and successfully in the field to protect against cattle-derived T. parva infection. The cattle were exposed in a natural field challenge site containing buffalo but no other cattle. The vaccine had no effect on the survival outcome in vaccinated animals compared to unvaccinated controls: nine out of the 12 cattle in each group succumbed to T. parva infection. The vaccine also had no effect on the clinical course of the disease. A combination of clinical and post mortem observations and laboratory analyses confirmed that the animals died of Corridor disease. The results clearly indicate that the Muguga cocktail vaccine does not provide protection against buffalo-derived T. parva at this site and highlight the need to evaluate the impact of the composition of challenge T. parva populations on vaccine success in areas where buffalo and cattle are present.