So you've got crypto?

This month, I just thought I’d share a bit of information on Cryptosporidium parvum, as I know it can be a confusing bug to get your head around and incredibly difficult to manage once it’s on your property.

Cryptosporidium parvum (often referred to as ‘crypto') is a protozoan parasite, rather than a bacterium (like e.coli or salmonella), meaning it is not readily treated by antibiotics.

Crypto is a common cause of scours in calves aged between four days and one month.

It is shed in the manure of adult cows who don’t show any symptoms of infection themselves. Calves usually become infected when they inadvertently ingest adult cow manure, often during the first 24 hours of life while still on their dam or in the calving paddock.

Once ingested, the protozoa invade the calf’s intestine and multiply, destroying the lining cells of the intestine, preventing nutrient absorption, and causing liquid diarrhoea that can last up to three weeks.

Huge numbers of infective crypto oocysts (eggs) are shed through the faeces of affected calves. To give this context, for each millilitre of manure from an infected animal, there are anywhere between one million to 100 million oocysts.

Immunity to crypto is slow to develop and these oocysts can re-infect that same calf as well as any pen-mates that come into contact with the infected scour.

Oocysts are very hardy in the environment and persist for long periods of time, commonly resulting in infection of the next group of calves entering the shed.

Sheds and pens should be thoroughly scrubbed and cleaned between groups to minimise faecal contamination, but it’s virtually impossible to eradicate crypto completely.

Crypto oocysts thrive in damp and dark environments and exposure to sunlight and drying can reduce infectivity in calf faeces after one to four days.

As calves age, they become less susceptible to infection and disease is less severe if/when they are affected.

Sickness due to Cryptosporidium in calves can be very high — affecting the majority of calves in the group, but death rates are usually low with good nursing (unless super-infection occurs due to repeated re-infection in the same animal or other pathogens are involved at the same time).

Where uncomplicated crypto infection occurs, the greatest losses generally aren’t usually from dying calves, but rather from losses associated with poor growth rates as the intestines take some weeks to repair.

The ongoing scour can result in dehydration, which if not addressed, can prove fatal. However, most calves with crypto as the only pathogen can be maintained with oral electrolytes during recovery.

Crypto is readily diagnosed using a faecal sample and a rapid test-kit in the field. Post-mortem samples and faecal floats can also be used if required.

Management of affected animals is mostly focused on fluid therapy and nutritional support — oral electrolytes or intravenous fluids in extreme cases, and milk feeds.

Antibiotics may be helpful if facing concurrent or secondary bacterial infections but are not considered the mainstay of treatment for straightforward crypto cases. There is no vaccine for crypto.

With crypto, it’s all about prevention and management.

Halocur can help prevent outbreaks by reducing replication of the parasite, thereby reducing the amount of oocysts shed into the environment. Halocur can help reduce the severity of diarrhoea in already-infected calves, however it should be used in consultation with your vet as it can be detrimental in dehydrated animals.

At the same time, the calf will be developing its own immune response to the parasite, so re-infection should be less of a problem after the Halocur course has finished.

Halocur administration is oral via a special applicator or syringe for accurate dosing, and usually starts on the first day of life (or as soon as the calves enter your property) and continues for seven days.

It’s important to remember that Halocur is far more effective as a preventative in newborn calves.

Aside from prevention and good nursing, management changes when faced with a crypto outbreak on your farm can include:

● All in/all out calf rearing. Avoiding mixed age groups and avoiding overstocking pens.

● Daily cleaning of calf tubers and calf feeders, or having dedicated feeders for each calf pen.

● Clean, ad lib fresh water (crypto loves water!).

● Cleaning and disinfecting calf pens between groups with an ammonium-based formula, ensuring all faecal material in pens is scrubbed clean.

● Increasing frequency of pick-ups from the calving paddock, or rotating calving paddocks.

● Fencing off crypto ‘breeding sites’ such as dark, damp areas under trees.

● Daily cleaning of calf trailers.

● Isolation of sick animals in a ‘hospital pen’ that is completely separate or walled-off from contact with other unaffected calves.

● Ensuring good colostrum management.

● Strategic use of the preventative Halocur.

Importantly, crypto is transferrable from cattle to humans.

I can personally vouch for its unpleasantness, and would recommend anyone working with sick calves practise strict personal hygiene.

Children, pregnant women and the sick or elderly should take extra care.

The author has no affiliations (financial or otherwise) with MSD Animal Health.

Lucy Collins is completing her Dairy Residency with The University of Melbourne. She works as an on-farm veterinarian for Apiam Animal Health, and alongside her partner on his family’s dairy farm in south-west Victoria. She is a 2021 Nuffield Scholar supported by Gardiner Dairy Foundation.