Background Bovine babesiosis, commonly known as redwater fever, is a sporadic tick-borne disease in the United Kingdom. Outbreaks occur during the spring, summer and autumn months when ticks are active. This study reports the findings of an investigation of an outbreak of bovine babesiosis during the winter month of February, 2019. Methods DNA from blood, organ and tick samples taken from affected cattle were tested for the presence of piroplasm and Anaplasma phagocytophilum DNA using PCRs directed to the 18S rRNA gene and msp2 gene respectively. The species of piroplasm was confirmed by sequencing. Results Babesia divergens DNA was detected in the blood of five cattle displaying clinical signs of babesiosis within a herd of twenty. This parasite was also detected in three of ten ticks removed from one of the affected cattle. In addition, A. phagocytophilum was detected in three cattle tested and two of ten of the ticks. Conclusions An outbreak of bovine babesiosis during February is unusual as the tick vector, Ixodes ricinus, does not generally become active until temperatures rise later in the year. February of 2019 was unusual as average temperatures during the first week of the month reached over 10 °C, well above historical averages that are typically below 5 °C, and a temperature at which ticks can become active. This unusual weather event is likely to have triggered tick questing, that combined with a co-infection with two tick-borne pathogens caused the severe outbreak of disease.

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 redcoloured urine. Copious ticks were noted on affected animals. Blood smear examination performed on sick animals detected piroplasms within erythrocytes, and a panpiroplasm 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 naïve animals into an endemic tick area. Co-infection also potentially increased severity of disease. The difficulties in controlling this outbreak are discussed. CASE PRESENTATIONThis outbreak occurred in a milking cow dairy herd with 180 Holstein-Friesian animals, located near Bodmin Moor in Vet Rec Case Rep.

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