Cryptosporidium is now the second most common cause of scouring in calves. Chloe Palmer finds out more about the impact of this parasite and how the risk of infection can be minimised.
The incidence of cryptosporidium infection in calves is now more commonplace and it poses a significant challenge to farmers because it is not easily treated.
Owen Atkinson, a veterinary consultant, says he sees many more cases of cryptosporidium now than when he first qualified 20 years ago.
“Cryptosporidium mainly affects calves between the age of four days and two weeks, although it can occur at any time until weaning.
Adult cattle are symptomless carriers but the calf is generally infected by its dam or a contaminated environment.”
Cryptosporidium is a small protozoa parasite which infects the small intestine. Known as oocysts, the eggs are shed in faeces and can persist for many years, being particularly resistant to disinfectants and drying out.
“Cryptosporidium is notoriously difficult to treat because there is no vaccine for it and the treatment options are limited. The infective oocysts are shed in huge numbers by infected animals and are very resilient, so the levels of infection can accumulate in buildings over time,” Mr Atkinson says.
“Immediately removing the calf from its dam is essential if you suspect cryptosporidium infection in a dairy herd. Clearly, for suckler herds, this is not possible. However, it is worth noting cryptosporidium is the only scour disease where antibodies from the colostrum do not give protection.”
Keeping the highest standards of hygiene is the best way to minimise the risk of cryptosporidium infection.
Mr Atkinson advises farmers to frequently clean calving areas and always house newborn calves in clean, disinfected pens, or rotate calving areas if outside. Any animals showing symptoms of infection should be isolated.
“It can be difficult to diagnose cryptosporidium without laboratory tests because the scour does not show any distinguishing features, such as a particular colour or texture.
“Similarly, there is no way of screening the herd for cryptosporidium and faecal samples of scouring calves must be tested by a laboratory or a vet for a definitive diagnosis.”
Mr Atkinson cautions farmers to be vigilant because calves will have already shed large numbers of oocysts by the time they are diagnosed with cryptosporidium, so rapid treatment is advised.
He says: “There is only one licenced product, Halocur, to treat cryptosporidium which is given as a drench. It is more effective when used preventatively and is administered to calves for seven consecutive days from 24-48 hours old.”
Care must be taken when administering the treatment as it can be toxic even in small quantities and it should only be used in conjunction with specific veterinary advice.
“It must not be given on an empty stomach and dosing correctly is imperative as even small overdoses can lead to illness. All newborn calves in the herd should be treated to break the cycle of infection,” he says.
Cryptosporidium also poses a significant threat to human health and Mr Atkinson says farmers handling infected calves should take precautions to prevent transfer of the infection to them and their family.
Other animals, including cats and dogs, can carry their own particular strains of the parasite.
Cryptosporidiosis infection in humans can cause severe diarrhoea and vomiting and is occasionally fatal in infants or those suffering from a compromised immune system.
The most significant outbreaks have occurred when drinking water supplies are contaminated with cryptosporidium. The most serious recent case was in 2005 following contamination of water supplied from Llyn Cwellyn reservoir in Snowdonia, where 231 cases of cryptosporidiosis were reported.
The Drinking Water Inspectorate imposes a rigorous sampling regime on all water companies in the UK. Dr Jodie Whitehead, catchment manager with Severn Trent Water, says cryptosporidium is one of the biggest challenges facing the company.
“Since the regulations were tightened in 2007 following the outbreaks in North Wales, the standard does not allow any cryptosporidium oocysts in the drinking water supply.”
Dr Whitehead points to the difficulties of treating cryptosporidium in the water supply because it is resistant to chlorine. Ultraviolet treatment, which efficiently deactivates the protozoa, is installed at boreholes but it is very expensive.
“Where we identify cryptosporidium oocysts in a drinking water supply with no treatment process in place, we will perform a risk assessment to determine whether we need to isolate the source from supply. We may need to take action to protect public health, such as asking customers to boil their water.”
Most historic cases of cryptosporidium contamination can be linked to faeces from livestock, particularly cattle, and Severn Trent Water is now working with farmers to raise awareness of the problem.
Dr Whitehead says: “We know livestock on land close to drinking water boreholes or surrounding surface water reservoirs present a risk of cryptosporidium infection.
“The problem is especially acute where large numbers of cattle poach ground close to a borehole because this causes soil compaction and, when the soil dries out, the fissures provide a pathway for water containing the oocysts to reach the water in the borehole.”
Dr Whitehead says where there is strong connectivity between surface and groundwater, there is an increased risk of contamination.
“Keeping livestock out of streams which run close to boreholes can reduce the risk of infection reaching groundwater by percolation.
Cross-compliance prohibits the spreading of slurry or manures within 50 metres of a spring or borehole.”
Grants to reduce contamination
Dr Whitehead is keen to work more closely with farmers with land on, or close to, boreholes.
“We have already run several awareness-raising workshops with farmers based near our boreholes.
“From April 2015, we hope to offer 50 per cent grants to farmers with land close to high risk boreholes for capital works to reduce the contamination risk.”
Dr Whitehead is pleased with the results from a small number of farms where Severn Trent Water has contributed towards the cost of fencing works, the creation of hard standing areas and the resiting of water troughs.
“Where we can invest in capital works which will remove or substantially reduce the contamination risk posed by cattle close to our boreholes, this is our preferred option,” says Dr Whitehead.
Greater awareness of the impact of cryptosporidium infection and taking action to reduce the risk of infection will also improve herd performance, Mr Atkinson says.
“Diseases which affect calf health might result in the loss of a relatively small number of calves but there is also the cost of treatment to consider.
“The greatest economic losses are often in the calves which survive as they are unlikely to reach the target weight for first service at the desired age and will take some time to catch up compared to the growth of healthy animals.”