Cryptosporidiosis Risk factors: Scientific report on Calf Shed Infections
4 August 2017

Introduction: This report from Australia advances our understanding of spread of rotavirus and cryptosporidiosis as well as other calf scour pathogens using advanced molecular methods.

Gunn et al (2016) report on two farms with calf scour pathogens. She identifies the sequence of events surrounding two sets of infections and monitoring with sensitive test methods for important calf scour microrganisms. In an earlier report by Gunn (2005) developed an extensive list of risk factors suitable for management. In this latest report a research team goes further and advances our understanding of which of those risk factors may be influencing cases of clinical calf scours. This latest work reports use new technological methods, describe their development, aimed at advancing the reliability and understanding of the epidemiology of the important causes of calf scours; these being in particular rotavirus, and cryptosporidiosis. In this report (Gunn et al 2016) discusses the scientific methods in detail. The results of applying the work included field examples of two ‘problem’ calf sheds to advance the understanding of how ‘breakouts of infection’ occur inspite of farmers applying recognised standards of care and hygiene. The techniques developed and used to demonstrate more precisely the origins of infection on farms includes the use of swabs to test for rotavirus and cryptosporidiosis on a number of surfaces including calf shed walls, gates, tractor trailers, and calf feeders including feeding teats. And also included calf excretion of the agents being studied. These tests were monitored over time; generally over 3 weeks to reach some specific conclusions for each of the two farms.

One aspect of the calf scours that applied to both farms was the importance of mixed infections. And while acknowledging the presence of both infections (rotavirus TypeA) and cryptosporidiosis, the scope of the research may have limited the interpretation of how important, or relevant to the results such combined infections may have had on the clinical signs seen. In unpublished work, David & Millward (2005) report that mixed rotavirus and cryptosporidial infections complicates the interpretation of the time sequence from infection; the appearance and severity of signs are delayed when rotavirus and cryptosporidiosis are infected simultaneously compared with each agent alone. An important variable not available for Gunn et als report (2016) is new research on the importance of the genotypic strain of Cryptosporidium parvum as reported by (Thompson 2016) on the severity of clinical signs. While this is not proven in her PhD thesis the results leave open that cryptosporidial subtypes or strains differ significantly in virulence, and how pathogenic different genotypic strains may appear from a clinical perspective, notably how severe the scours (tendency to dehydrate), the loss of appetite, and period of recovery from scour can differ. In the practical farm situation there is a lack of knowledge about cryptosporidial challenge dose rate occurring, the inability to measure ‘stress’ in the very young calf, and in general the imprecise measurement of colostral transfer while following high standards of colostrum feeding to a group of calves. Taking these variables into account it is therefore difficult to apply the results above (Gunn et al 2016) to any other farm other than the two reported on. This report however does emphasise the presence of both organisms, one a virus and the other protozoan and their widespread presence in the calf rearing units from birth and in the shed environment. The use of these new tools to detect their presence is an advance in our understanding. They emphasise the importance of between calf transmission in advance of clinical signs of scouring.

Results:

Both rotavirus and Cryptosporidium parvum were found on a number of surfaces after swabbing.

There were some differences between farms and the report discusses these in further detail.

The use of Halocur on one farm (B) delayed significant shedding of oocysts, with only 30% shedding before 14 days. Halofuginone is considered to be more effective with lower challenge doses.

These reports produced on these two farms are open to a number of opportunities to propose what and how these infections occurred. These comments (BAPauling) do not necessarily reflect the conclusions of the report prepared by Gunn et al in her report. The full report should be examined to become familiar with each farm’s management and the interpretation of the results obtained.

Details of the findings are attached. The comments are made from a personal perspective and should not be seen as criticism of the management of the calf units or the research undertaken and reported on.

 

Hygiene standards in preparation failed to deliver a clean pen wall. “Hardy” viruses (includes rotavirus) and surface disinfection requires sterilisation standards to be achieved to reduce risks. Multiple cleaning attempts e.g steam cleaning repeatedly and allowing to dry (pers comm.). Sterilisation of the surface means a smooth wall structure – non-porous, with no residual organic matter.
This will not address the problem of the carrier cow excretor infecting the calves.
Interpretation, the floor bedding is clean at the start,
with the contamination subsequent to the expression of infection from wall to calf so that there is rotavirus excretion to floor (day 3 – 5),
Or
Contamination from calf infection from the dam (and fomites) at birth and a new infection expressing itself as contamination over the bedding. The graph below suggests nthat 40% of calves are excreting rotavirus from about 3 days and it is the dam and/or fomites including feeding utensils which is important.
Once rotavirus infects one part of the system, the wall, or from the cow, the virus becomes ubiquitous – everywhere and transfers to feeding equipment, meaning there is virtually no rescue available to prevent further infection.
The goal without hygiene practices changing may be limited in scope and success.
In the season reductions in severity may be possible – reducing the length of time of scouring may be the best goal.
It is reported that empty pens were cleaned with Virkon, a product which is known does not inactivate cryptosporidial oocysts. A change of surface preparation is required, using physical and then chemical disinfection. Very low levels (e.g 10 -60 oocysts) may have been enough for infection to start from walls and recycling of crypto in a calf
Refer to Practical Disinfection (www.pvd.co.nz)
It is possible that the rotavirus mixed infection was delaying the expression and recycling in the calf with mixed infections. This appears to be a likely explanation. (David & Millward 2005).
The graph suggests that less than optimal hygiene standards of feeding equipment reflected by crypto presence associated with feeding equipment before and around day 9 and with the prepatent period of 2 -3 days, this difference is the prepatent period for cryptosporidial infections. i.e. bedding contamination occurs at days 12-14.
What is important is that a significant number of calves are excreting prior to contaminatiomn of feeding utensils. So earlier transfer between calves may mean cow to calf, calving-down pad transfer, or transfer from trailer contamination.
See comments above.
Detection of crypto on feeding equipment is compounded with the number of calves excreting in the first 9-11 days. The origin of this expression at day 9-11 on feeding equipment of the expression suggests direct contact cow to calf, and calf to calf may be more important for crypto to spread the problem within the calf pen environment in the first 7-10 days. The mixed infections with rotavirus delayed expression of signs of crypto.
Competitive exclusion of crypto expression when mixed infections, but generally more serious clinical signs occur than that of crypto infection alone (David & Millward).
The important feature is the detection of crypto before 9-11 days. It was only then that there was detection on penwalls, and feeding equipment, followed by bedding. See comments above.
Infection with rotavirus was simultaneous with that of crypto, but with a shorter prepatent period the infection of rotavirus appears to pre-exist that of crypto. This may not truly reflect the source of the calf shed infections; cow to calf, calf trailer to calf while the calf is in transit from calving down to the calf shed.
If rotavirus is present the infectivity rate and % of calves infected reaches a high level of the calves at risk.
If crypto is present with only a low number exposed at the start of life, ultimately the infection rate will reach 100% in the period prior to 3 weeks. The shift from infections to clinical scouring sick calves may be more related to the genotypic strain, load dose ingested of oocysts (Thompson 2016 ), colostrum feeding, gut microbiome, stressors and availability of attachment sites in the immature gut lining. Included in this gut manageement is the use of probiotics, though there is no consensus as to which strains may offer ‘real’ and meaningful benefits.

Conclusions:
1. Mixed infections of young calves less than 3 weeks, of rotavirus and cryptosporidiosis started probably from the cow or the calving environment/trailer (or the transfer from fomites) in the first few hours/days; very early in the calf’s life.
2. The multiplication and shorter prepatent period for rotavirus overwhelms the appearance of cryptosporidiosis infection.
3. A faecal sample of early aged calves (less than 6 – 8 days) in mixed infections may therefore miss many of the pending infections of crypto.

Disinfection and Hygiene:
In my opinion there requires to be a change to disinfection materials and methods in the preparation of calf pens. And without more rigorous hygiene protocols for cleaning of feeding utensil any attempt to see the effects of change to disinfection procedures is likely to fail. The finding that the organisms can be found on trailers used to transfer calves also identifies more rigorous standards eg regular water blasting and steam cleaning. the same advice is provided by Moore et al (2010, 2012).

References:
David & Millward. Compositions and vaccines containing antigen(s) of Cryptosporidium parvum and of another pathogen. USA Patent 2005 US 20050106163 A1
Gunn A, J House (2005). Calf Scours in Southern Australia. Beef Enterprises Phase 2. Project code: AHW.057 Published by Meat & Livestock and University of Sydney, Australia
Gunn A, J House, P Sheehy, A Thompson, D Finlaison, P Kirkland (2016), B.AHE.0025 Molecular methods for detection of calf scour pathogens. Pub.: Meat and Livestock Australia Limited The University of Sydney and NSW Department of Industry and Investment.
Moore D, K Heaton, S Poisson, WM Sischo (2010). Calf Housing and Environments Series. V. Reducing Pathogen Load in the Calf Environment. Pub Washington State University Dec 2010
Moore DA, K Heaton, S Poisson, WM Sischo (2012). Dairy Calf Housing and Environment:The Science Behind Housing and On-Farm Assessments. Pub. Washington State University
Thompson, Sarah (2016). Cryptosporidiosis in farm livestock. PhD thesis. http://theses.gla.ac.uk/7096/. Submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy, Institute of Biodiversity Animal Health and Comparative Medicine. University of Glasgow 2016

July 2017:
Bruce Pauling is a veterinarian and director of Professional Veterinary Distributors, having researched, and developed Kryptade and Exagen registered veterinary medicines in New Zealand for aiding the prevention and treatment of calf scours associated with Cryptosporidium parvum.