Cryptosporidiosis Poses Major Challenge to Scottish Cattle Herd

The severe impact of Cryptosporidiosis on the Scottish cattle herd was highlighted today (June 14th) at the launch of Quality Meat Scotland’s Research & Development report.

Speaking at the launch, Sarah Thomson, PhD student at Moredun Research Institute, said that according to veterinary surveillance reports cryptosporidiosis has increased as a diagnosed cause of scour in calves.  Veterinary surveillance reports showed, she said, that in 2011 Cryptosporidiosis was responsible for 35% of scour outbreaks in calves less than one month old in Scotland.

However, despite its importance to the health of the national herd, very little is known about the different strains causing disease present in Scotland and the control method options are limited.

“Cryptosporidiosis is of great importance to the UK livestock industry. Infected animals may suffer from diarrhoea, loss of appetite and dehydration and in severe cases infection may cause death. Those most at risk are young livestock around 2-10 days old.

“One infected animal can produce enough parasites to infect 1000 million other animals which is a phenomenal amplification rate,” observed Ms Thomson.

Cryptosporidiosis is a parasitic disease which infects animals and humans. It is caused by a tiny single celled organism called Cryptosporidium which is invisible to the naked eye.

The parasite is transmitted orally, through the consumption of the oocyst (egg) stage of the parasite which is shed in the faeces of infected animals. Once inside the animal the parasite attaches to the gut wall and causes damage to the intestine resulting in disease.

A previous QMS project, CRYPOBEEF, revealed the increased severity of Cryptosporidiosis on farms in two areas of North East Scotland, where some of the units reported losses of up to 30% of calves.

“At present, control strategies for Cryptosporidium are limited. There is no vaccine to prevent cryptosporidiosis and treatment options rely largely on rehydration therapy,” said Ms Thomson.

“The oocysts (eggs) are highly resistant to common disinfectants and can survive and remain infective for long periods of time in the environment. This combined with the low minimum infectious dose makes Cryptosporidium a real challenge to control on the farm,” she added.

Frustratingly, very little is known about the species and strains of Cryptosporidium found in Scotland and even less is known about the pathogenicity of the different strains.

Initial testing of samples collected from young calves, for the presence of Cryptosporidium DNA, showed that all calves were positive for Cryptosporidium in the first six weeks with peak shedding of oocysts occurring in week three. Interestingly, over half the samples from calves were found to be positive for Cryptosporidium at six months of age.

Tests have shown that, in the first six weeks, most animals were shedding Cryptosporidium parvum with mixed infections and other species making an appearance from week three. Positive samples at three months were identified as Cryptosporidium bovis and Cryptosporidium ryanae which are the species most usually expected with this age group. These species have not been associated with any clinical signs at present.

“What is more unusual is that the majority (70%) of positive samples at six months were identified as C. parvum. This is unusual because most literature suggests that after six weeks animals will no longer shed or be infected with C. parvum,” she observed.

The key findings of the on-going work are as follows:

• Cryptosporidium is prevalent in calves up to at least six weeks with the most predominant species being C. parvum

• Contrary to current scientific belief based on previous findings, C. parvum was also the most prevalent species detected in calves at six months on one farm

• The same species and genotypes of Cryptosporidium are generally present on farms year after year

• Calves may be shedding Cryptosporidium even if they do not show clinical signs