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Mucosal Disease: Field Observations
Frank Nottle BVSc District Veterinarian, COONABARABRAN
INTRODUCTION
Pestivirus infection is becoming increasingly recognised as a cause of lost productivity in the cattle industry. This is both for its effect on fertility and the illthrift - mortality syndrome. With all diseases there is value in examining the field manifestation of a disease entity of a period of time to determine if the disease is conforming to its expected pattern. This paper will present the available information on pestivirus infection in the Coonabarabran Rural Lands Protection Board District over the past ten years.
There will be no in-depth presentation of the full scientific aspects of the disease. For those desiring this information, the review by Dr Ian Littlejohns as published by the Sydney University Post Graduate Foundation is suggested as a starting point.
BACKGROUND INFORMATION.
Coonabarabran Rural Lands Protection Board district is located around the Warrumbungle Range in north-west New South Wales. Rainfall is non-seasonal at around 700mm. There are 850 properties running beef cattle with a total of 150,000 head. Calving takes place in late winter - early spring. Most young stock are sold as yearlings though there is a growing trend towards the heavier steer market.
Investigations were undertaken in the majority of cases in this paper because illthrift or abortion/stillbirth outbreaks. Tests used were the Gel Diffusion Precipitation Test (GDPT) on serum and virus isolation from blood. During 1990 the Elisa (Antigen Capture) test was introduced and run in parallel with virus isolation.
TREND OF PESTIVIRUS INVESTIGATIONS
As the level of understanding of clinical manifestations of pestivirus infection has increased over the past decade so has the level of laboratory submissions requesting pestivirus investigation. From 1981 to 1985 there were 4 submissions From 1986 to 1990 there were 50 submissions These were split by presenting problem as follows:
| Illthrift | 26 |
| Stillbirth/Abortion | 14 |
| Calf Deformities | 4 |
| Febrile Disease | 10 |
PESTIVIRUS PREVALENCE
Of 38 properties where sufficient samples were taken to give a fair chance of showing infection only three were free from the evidence of pestivirus activity. This level of 92% infected herds is in accord with previous surveys.
LEVEL OF INFECTION IN ADULT FEMALES
The infection rate in adult females should give an indication of the likely occurrence of infertility and congenital problems in their calves. The table below lists the number of herds with that level of infected females in the percentage ranges.
| FEMALES INFECTED | NO. OF HERDS |
|---|---|
| 100% | 5 |
| 80 - 90% | 2 |
| 60 - 70% | 2 |
| 40 - 50% | 1 |
| 20 - 30% | 2 |
| 10% | 2 |
| 0% | 3 |
These results would indicate that there is the potential for a wide range of infertility and congenital abnormalities to be seen. However in this series of cases pestivirus infection could not be shown to have caused any such events. This is not in accord with the observations of field veterinarians in other areas.
ILLTHRIFT INVESTIGATIONS.
A protracted illthrift syndrome is the usual outcome for a calf infected in utero with pestivirus. Damage to the mucosal surfaces is common with expected gastro-intestinal and respiratory tract effects.
The clinical signs observed in cattle where pestivirus was isolated were as expected. The age of the animals ranged from 6 to 36 months with 90% 18 months of age or younger. The clinical signs were seen in the following percentage of cases where pestivirus was isolated associated with illthrift.
| Clinical Signs | Animals Showing Sign |
|---|---|
| Diarrhoea | 72% |
| Oral/nasal Mucosal Erosions | 61% |
| Skin Changes | 44% |
| Lameness | 22% |
| Chronic Bloat | 11% |
Low packed cell volumes were seen in 5/5 animals tested. These ranged from 13% to 27%. Total white blood cell counts were low to normal ranging from 2.75 x 10g/l to 8.7 x 10g/l.
DIAGNOSIS
It is recognised that some cattle that are positive to the Gel Diffusion Precipitation Test will be carrying the virus. 5 animals fitted this category in this survey. In many cases if a positive G.D.P.T. is found, virus isolation does not proceed due to the cost. As such, a percentage of carrier animals is missed. The Elisa test should overcome this.
'NATURAL' VACCINATION
In order to exposure replacement heifers to pestivirus infection, known carrier animals have been run with them to provide 'natural' vaccination. In three herds where this has been done no cases of mucosal disease illthrift were seen in subsequent calf drops.