New Zealand researchers are reported to have proven that sheep can carry and potentially spread the parasite behind the bovine anaemia epidemic.
Sheep are asymptomatic carriers of the tick-borne parasite Theileria orientalis. This means they are unaffected by the disease but can spread it to ticks which feed on them.
The researchers suggest this could explain how the disease spread so quickly through the North Island after the outbreak in 2012.
The research, published in Veterinary Parasitology, was undertaken by scientists at Massey University and AgResearch with funding from Massey University Research Fund and the Lewis Fitch Research Fund.
The authors are K.E.Lawrence, K.Gedye, R.Hickson, B.Wang, L.Carvalho, Y.Zhao and W.E.Pomroy
The Abstract says:
Theileria orientalis is a tick‒borne intracellular parasite of red blood cells that causes severe and mild infections in various ruminants worldwide.
To date there have been 11 types identified within this species, of which 4 types are presently found in New Zealand cattle.
Since 2012, New Zealand has suffered a substantial epidemic of infectious bovine anaemia in both dairy and beef cattle associated with the Ikeda type. The speed at which the disease spread through the North Island suggested that other species could have been involved in transmission.
The aim of a series of related experiments was to test the null hypothesis that sheep cannot maintain T. orientalis Ikeda type infection or infect ticks that feed on them.
Several studies were conducted over two years to address this hypothesis which together showed that sheep can have detectable levels of T. orientalis Ikeda type infection in both the acute and chronic phase and that Haemaphysalis longicornis larvae can become infected when feeding on sheep.
No anaemia, weight loss or clinical disease was recorded in the sheep in the acute phase of infection.
The levels of infection recorded in the sheep were much lower than those found in cattle, consistent with the sheep being asymptomatic carriers of T. orientalis Ikeda type infection.
Link to research (DOI): 10.1016/j.vetpar.2021.109391