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Bovine Protozoal Abortion in North-Eastern NSW

P.A.W. HARPER Grafton Agricultural Research & Advisory Station, GRAFTON, NSW 2460

The diagnosis of protozoal abortion in cattle is based on demonstration of characteristic histologic lesions in the aborted foetus; focal or multifocal non-suppurative inflammation in the brain, heart, liver and occasionally other organs, and less commonly, demonstration of protozoan cysts in tissue sections. A protozoal organism similar to the newly described protozoan infection of dogs Neospora caninum (Dubey et al. 1988) has been implicated as a major cause of abortion in dairy cattle in California (Thilstead and Dubey 1989; Anderson et al. 1991; Barr et al. 1991). The recent demonstration that N. caninum can be transmitted trans-placentally in cattle and cause non-suppurative necrotising encephalitis and foetal mummification respectively in the foetus (Dubey et al. 1992) confirms the potential pathogenic role of N. caninum in bovine protozoal abortion.

In Australia, bovine protozoal abortion has been recognised by diagnostic pathologists for a number of years. The disease has been presumed to have been due to infection with Sarcocystis species (McCausland et al. 1984) or more recently Neospora-like protozoa. This paper reports the findings of a ten year retrospective study of bovine protozoal abortion in an area where the disease is recognised as a major cause of reproductive failure, and presents immunological confirmation of the role of N. caninum in at least some of these cases of abortions.

Protozoal abortion is considered to be one of the most important causes of abortion in north-eastern NSW cattle herds. Retrospective examination of 200 cases of bovine abortion, where the whole foetus was submitted to the Regional Veterinary Laboratory at Wollongbar, determined that 17% were diagnosed as due to Protozoal abortion (Table 1). Further, in the 10-year period from 1983 to 1992 inclusive, officers at the Regional Veterinary Laboratory Wollongbar diagnosed protozoal abortion as the cause of the loss of 96 foeti from cows from 89 farms in the region. The laboratory records of the 96 cases, all of which were diagnosed by demonstration of histological lesions characteristic of the disease, were examined and owners of properties contacted. Owners were surveyed as to enterprise types, stock numbers, management procedures, size of property, grazing type, presence of dogs and their management, presence of foxes and feral dogs, presence of neighbours dogs, presence of domestic and feral cats and type of food given to domestic animals, whether baiting had been used and how often, numbers of cattle abortions in the year diagnosed, in previous years and in following years, size of aborted foetuses, whether foetal mummification was observed, whether illness in cows prior to abortion was observed and whether silage hay or concentrates were routinely fed.

The numbers of bovine protozoal abortions diagnosed by year is given in Table 2. Between 5 and 9 diagnoses were made per year with the exception of 1985, 1991 and 1992. Concerted efforts were made in 1985 at the cessation of Brucella abortus testing, and in 1991, to encourage the submission of foeti to the laboratory, explaining the rising number of diagnoses in recent years. A regional distribution of diagnoses by Rural Lands Protection Boards is given in Table 3. Similar numbers of diagnoses were made throughout the region, with the exception of Gloucester, in which a majority of aborted foeti were submitted to Elizabeth Macarthur Agricultural Institute. Of the 89 farms confirmed infected, 57 were dairies and 32 were primarily beef enterprises.

In all cases the whole foetus was submitted to the laboratory and in the majority of cases, lesions of non-suppurative inflammation were detected in more than one organ, the most common being the brain and heart. The distribution of lesions in the 96 cases are presented in Table 4.

The month in which the diagnosed abortion occurred is presented in Figure 1. The most common month in which abortions occurred was July, however the seasonal calving patterns for north coast dairy and beef herds are autumn and winter/spring respectively, so abortions would be expected throughout the year, particularly since the drought of 1990-92 has led to widespread late calving in beef herds.

On farms in which three or more abortions had occurred in recent history (i.e. within three months) were classified as abortion 'outbreaks', whereas those with less than three recent abortions were classified as 'sporadic' abortions. Thirty-eight of the affected farms were classified as outbreaks and the remainder considered sporadic abortions. Estimated gestational age of the foetus at the time of the abortion is given in Table 5. Protozoal abortions were diagnosed throughout the full gestational range of foeti submitted (foeti <4 months are rarely submitted). A number of calves died postnatally with lesions of the disease, however were not included in the study as they were not considered abortions. Foetal mummification was reported as occurring during three outbreaks of abortion, during which protozoal abortion was diagnosed in at least one foetus submitted.

The anti-N. caninum immunoperoxidase technique (Lindsay and Dubey 1989) was used in tissues from eight foeti from the study with positive demonstration of both tachyzoites and cysts of Neospora caninum in the brain of one aborted calf and individual tachyzoites in the brain of another confirming the role of N. caninum in bovine abortion in north-eastern NSW. N. caninum which has been isolated from dogs (Dubey 1990), has been implicated by immunological methods in some cases of abortion in cattle in Tasmania and south-western New South Wales (Obendorf and Mason unpublished; Philby and Dubey unpublished).

Contact was made with 79 of the 88 farms in which diagnoses was confirmed and information collected on the epidemiology of the disease. The majority of infected properties reported the presence of foxes (95%) with the presence of domestic cats (79%), feral cats (63%), domestic dogs running freely (61%) and neighbours dogs running freely (63%), with feral dogs and dingos being reported (61%). An overwhelming majority of properties reported bushland present, adjacent to or at least within 10 kilometres (78%). In the light of present knowledge it is likely that the disease involves N. caninum and possibly other organisms transmitted by carnivores, and that control of carnivores be applied in the vicinity of outbreak areas. This requires consideration of several strategies including: tethering of domestic dogs, restricting their access to pastured areas; feeding domestic dogs on cooked or dried proprietary feed preparations, and assisting in control and eradication of foxes, feral cats and wild dogs. An Agnote has been distributed in the region to assist in the promotion of laboratory submissions as the diagnostic method of choice in diagnosing bovine protozoal abortion.

Acknowledgements

The efforts of R.W. Cook, P.A. Gill, G.C. Fraser and J.R. Boulton of the Regional Veterinary Laboratory, Wollongbar, NSW, 2477, in diagnosing the disease, and J.P. Dubey of the Zoonotic Diseases Laboratory, Livestock and Poultry Sciences Institute, Agricultural Research Service, US Department of Agriculture, BARC-East, Beltsville, Maryland, 20705, USA, in performing the immuno-diagnostic tests is gratefully acknowledged.

References

Anderson MI, Blanchard PC, Barr BC, Dubey JP, Hoffman RL and Conrad PA (1991). J. Am. Vet. Med. Assoc. 198:241

Barr BC, Anderson ML, Dubey JP and Conrad PA (1991). Veterinary Path. 28:110

Dubey JP, Carpenter JL, Speer CA, Topper MJ and Uggla A (1988). J. Am. Vet. Med. Assoc. 192:1269

Dubey JP (1990). Comp. Cont. Ed. 12:653

Dubey JP, Lindsay DS, Anderson ML, Davis SW and Shen SK (1992). J. Am. Vet. Med. Assoc. 201:709

Lindsay DS, McCausland IP, Dubey JP, Badman RT, Hides S and Slee KJ (1989). Cornell Vet. 74:146

Lindsay DS and Dubey JP (1989).American Journal of Veterinary Research 50:1981

Thilstead JP and Dubey JP (1989). Journal of Veterinary Diagnostic Investigations 1:205

Table 1. Causes of 200 cases of abortion in north coast cattle, where the whole foetus was submitted to the laboratory

	%
Septic (non-specific bacteria)	18.0
Protozoan	17.0
Leptospirosis	10.0
Vibriosis	6.5
Deformity (Akabane virus, etc.)	6.5
Dystocia/trauma	6.5
Other	2.5
Pestivirus	1.5
Undiagnosed	31.5

Figure 1. Month in which diagnosed abortion occurred

Table 2. Bovine protozoal abortions diagnosed at RVL Wollongbar, 1983-1992

Year	Number of foeti
1983	5
1984	1
1985	14
1986	6
1987	9
1988	8
1989	6
1990	8
1991	16
1992	23
TOTAL	96

Table 3. Bovine protozoal abortions diagnosed by Rural Lands Protection Board

RLPB	Number of farms
Gloucester	6
Kempsey	22
Grafton	19
Casino	21
Tweed/Lismore	21
TOTAL	89

Table 4. Distribution of lesions in 96 cases of protozoal abortion

Lesions	Number of cases
Encephalitis only	30
Encephalitis, myocarditis	37
Encephalitis, myocarditis, plus hepatitis, etc.	18
Encephalitis, hepatitis only	2
Myocarditis only	8
Hepatitis only	1
TOTAL	96

Table 5. Estimated gestational age of foetus at time of abortion

Age of foetus	Number of foeti
> 4 months to ≤ 5 months	25
> 5 months to ≤ 6 months	16
> 6 months to ≤ 7 months	23
> 7 months to ≤ 8 months	15
> 8 months to ≤ 9 months	7
TOTAL	96

Table 6. IgG levels in 24 cases of bovine protozoal abortions diagnosed

IgG level	Number of foeti
≤ 80	6
> 80 ≤ 200	5
> 200 ≤ 500	10
> 500	3
TOTAL	24