Protozoal Disease in Cattle
Anne Abbs BVSc CertVPH(MH) MRCVS
Coccidia and Cryptosporidium are both protozoal parasites that can cause
infection in young animals, particularly calves, leading to scour which is
frequently fatal if left untreated. Protozoa are spread by a resistant infective
stage called an oocyst that can survive outside the host animal.
Cryptosporidium generally occurs in calves up to 2 weeks old but coccidiosis
can cause disease in animals up to a year old. Thereafter animals can carry,
be infected and excrete oocysts but not show disease. Infected calves shed
massive numbers of oocysts that can survive in a moist environment for many
weeks. Infection can rapidly multiply if young calves are mixed with older
calves or pens are used repeatedly, allowing a build up of oocysts to occur.
Protozoa cause severe damage to the lining of the intestine and calves that
survive the infection will show stunted growth and poor condition for some
time.
Mixed infections with other agents such as Coronavirus, Rotavirus or E-coli
can often occur, exacerbating the problem. Good colostral uptake is vital to
help protect calves against other infections and reduce the severity of disease
when multiple agents are involved.
Reduction of oocyst numbers (and environmental challenge with other
pathogens like coronavirus) can be achieved with aggressive cleaning of
contaminated areas. Ideally all organic material should be removed and
surfaces are subjected to a steam clean. A disinfectant should be applied and
the areas should be allowed to dry. If possible the shed should be left empty
for at least 8 weeks and preferably 4 months. Ultra-violet light will also kill
oocysts – to take advantage of this, clean equipment can be left out in the sun
when not in use.Calves will be exposed to infection in the calving pens –
using the regime above on these pens or calving outside will reduce
exposure.
Halocur® can be used as a preventative treatment for Cryptospiridia, which
should start 24 - 48hrs after birth. Halocur® reduces shedding of oocysts but
does little to help with survival rates or cure diarrhoea – do not rely on
Halocur® when moving sheds and cleaning aggressively is more effective).
Treatments can be also be given for coccidia, but once a calf shows clinical
signs then intestinal damage will very often be advanced so once coccidiosis
is diagnosed, it is preferable to treat animals at the time that risk is most
anticipated and before clinical disease is apparent. Veterinary advice should
be sought as to the best treatment to use in individual circumstances, not
forgetting control is far better than treatment.
Protozoa can be difficult organisms to deal with as they are resistant to attack
outside of the host. Hygiene, good colostrum intake and preventative
treatment all play a role in their control, allowing calves to grow efficiently.