High morbidity associated with an outbreak of tick-borne disease in a dairy herd, Cornwall

In April 2020, animals in a herd of 180 dairy cows began displaying pyrexia, milk drop and condition loss. Some animals aborted while others developed anaemia and red-coloured urine. Copious ticks were noted on affected animals. Blood smear examination performed on sick animals detected piroplasms within erythrocytes, and a pan-piroplasm PCR and sequencing confirmed the presence of Babesia divergens. Further PCR testing detected Anaplasma phagocytophilum in some of the animals. In a number of animals, co-infection with both pathogens was demonstrated. A range of control measures were implemented with varying levels of success, and clinical cases continued until winter housing of cows in November. A total of 61 animals were affected. The main contributory factor in this case was likely buying in of large numbers of naive animals into an endemic tick area. Co-infection also potentially increased severity of disease. The difficulties in controlling this outbreak are discussed.

Automated summary

An outbreak of Babesia divergens and Anaplasma phagocytophilum co-infection occurred in a herd of 180 dairy cows in April 2020, affecting a total of 61 animals. The main symptoms included pyrexia, milk drop and condition loss, and the source of the outbreak was likely due to the introduction of naive animals into an area endemic for ticks. Co-infection potentially contributed to the severity of the disease, leading to difficulties in controlling the outbreak.