Wild deer as vectors of anthelmintic resistant gastrointestinal nematodes between cattle and sheep farms

Take-home Message: Wild deer do have the potential to transmit anthelmintic resistant gastrointestinal nematodes to cattle and sheep. 

Wild deer could potentially transmit anthelmintic resistant gastrointestinal (GI) nematodes to cattle and sheep, according to scientists in Scotland and Bristol who demonstrated the existence of Benzimidazole-resistant Haemonchus contortus in wild roe deer.

GI nematode parasites are one of the main causes of productivity loss in cattle and sheep production, as well as being a threat to animal welfare. Over-reliance on broad-spectrum anthelmintics to control these parasites has led to the development of anthelmintic resistance on cattle and sheep farms in the UK.

“Previous studies have demonstrated that, at least under experimental conditions, deer can become infected with bovine and ovine species of GI nematodes,” said Cosmin Chintoan-Uta, from The Roslin Institute in Edinburgh.

“So we set out to examine the population of GI nematodes in wild deer in the South West of England and aimed to identify whether wild deer could act as vectors of anthelmintic resistant GI nematodes between cattle and sheep farms.”

A total of 48 samples, comprising the abomasa and small and large intestines, were collected from fallow, red and roe deer. Samples were collected from three types of environment: ‘farmed’ deer with no contact with other wildlife or livestock; wild deer grazing in areas of ‘extensive’ cattle farming and wild deer grazing in areas of ‘intensive’ cattle and sheep farming.

To study the nematode GI population of these wild deer, the total adult abomasal nematode count was estimated from a 10% aliquot of abomasal contents in individual deer by visual identification of adult male nematodes.

Benzimidazole (BZ) resistance was investigated in these nematodes by isolating and sequencing the beta tubulin gene and surveying the resultant sequences for BZ-related mutations.

In order to confirm the potential of cross transmission, one calf was infected with approximately 10,000 larvae cultured from nematode eggs extracted from wild roe deer and one lamb was infected with approximately 4,000 larvae cultured from nematode eggs extracted from the calf.

Nematode eggs extracted from the faeces of the lamb were used in an Egg Hatch Test for detection of BZ resistance in H. contortus and a half maximal effective concentration (EC50) value was calculated to assess BZ resistance status.

“We found that wild roe deer grazing in the ‘intensive’ environment had a significantly different abomasal nematode fauna compared to red and fallow deer,” said Mr Chintoan-Uta. “These differences were irrespective of the type of environment in which the latter two grazed.

“Furthermore, the species of deer was the main influencing factor of adult abomasal nematode fauna, while the environment had a small effect in roe deer.

“The nematode larvae cultured from wild roe deer successfully established an infection in the calf, with 90% of the nematodes established being H. contortus. Larvae cultured from this calf successfully established a high level infection (more than 1,300 adult H. contortus estimated in the abomasum) in the lamb, with H. contortus being the only species identified.”

Mr Chintoan-Uta added that further research was required to determine whether cross-transmission occurs under field conditions and to determine the extent of this cross-infection.

Full details: Chintoan-Uta C, Morgan ER, Skuce P, Stafford K, Au C, Bevan E and Coles GC: “Deer can become infected with bovine and ovine gastrointestinal nematodes and can transmit anthelmintic resistant nematodes to cattle and sheep.”

For further information contact: BSAS on 01314 454508