This report is a description of trials reported in a patent application(not an ideal research reference). It reports on the impact of single infections compared with mixed infections involving rotavirus and cryptosporidial infections across a range of criteria measured.
Ref: USA Patent 2005/0106163: David & Millward
Calves were artificially infected with rotavirus, or cryptosporidium, or a mixed infection of each.
Calves were challenged on day 1 of life. There were 4 groups of 6 calves. Challenges were with known pathogenic strains of each organism.
Observations included rectal temperature, general condition, anorexia, diarrhoea, dehydration, and death.
Anorexia was considered present if a calf took less than 2 litres of milk. (NB: Many young calves about 20-25 kg do not drink 2 litres of milk per feed especially for the first 3 – 4 days of life)
Score 1 is calf with signs, Score 0 is without signs
Calves were observed twice daily for 10 days following inoculation with challenge strains.
(Control calves not shown).
Oocyst numbers were markedly increased when the combined infection was present with the highest numbers occurring late in the study period.
Rotavirus excretion is extended with mixed infections with higher numbers of infectious particles in faeces compared with the virus infections alone.
Dehydration is noticeably more severe with mixed infections coinciding with the appearance of crypto oocysts (graph 1 above).
Calves were equally affected by each of the infections, and timing of this effect is related to the incubation period for each disease.
However the mixed infection had a more severe effect, starting earlier, and lasting longer.
The loss of appetite was noticed in all groups from day 1-3 days of age, irrespective of treatment.
This may reflect the natural (lower) volume intake of newborn calves.
The combined infection did increase the severity over the first 3 days, and persisted to day 10. Crypto infection alone also had an extended period with loss of appetite. The effects of the combined infection was additive in how severely calves appetite was affected.
Calves challenged with both rotavirus and cryptosporidium suffered the clinical signs of calves infected in the field with changes to appetite, scours, and dehydration. There were also changes in condition reflecting general discomfort, and progressed to death in some instances. The cause of each death however was not commented on.
The severity of signs were noticeably more severe, and the signs progressed over an extended period when there was mixed infections present. For some of the signs there appeared to be synergism between rotavirus and Cryptosporidum parvum.
Noted Features included
- Rotavirus excretion was high even if signs were not as severe as cryptosporidial infections. It suggests virus contamination may be highly significant. Challenge doses in the field may gradually increase with time in a calf shed.
- In a mixed infection, rotavirus may have disappeared by the time a sample of faeces is taken for diagnostic purposes. The sensitivity of the test method in this report is not given.
- Dehydration was very much more severe with cryptosporidial infection. However no mention is made of the effectiveness of rehydration therapy for each of the 3 infectious challenges.
- A combined infection produced an extended period of loss of appetite, and dehydration compared with either disease alone. It was noticeable that in this case that the signs were at its most severe after 10 days of age, though there was also considerable signs of infection from day 6.
Outcomes for Calf Rearing in the Field
- Increased numbers of calves being managed will produce severe effects on limited labour available.
- Calves will accumulate in hospital mobs as more calves join the ‘sick’ mob.
- And there will be delays in ability to release these calves into the recovered normal groups.
- Recovered calves may still be excreting significant numbers of oocysts, so isolation must be maintained from normal calves. It is likely that these will already have been infected though.