Neospora caninum, a microscopic protozoan parasite, was first described in 1988 and has since been shown to be a major cause of bovine abortion throughout the world.
In some areas, such as north coast of NSW, Neospora caninum is thought to be responsible for more than 30 per cent of all abortions in cattle. Initial investigations in North Queensland dairy herds estimate that about 26 per cent of cattle are infected with this parasite. A recent research project on 3700 beef cattle from 25 management groups across Queensland has shown that Neospora caninum was present in all herds. Also, researchers in the United States have reported a 5 per cent decrease in milk production in infected first-lactation dairy heifers and decreased weight gains in infected beef cattle.
Neospora infections have also been reported from many other animals, including dogs, sheep, goats, horses and deer. Additionally, a close relative of this parasite, Neospora hughesi, has recently been described from horses.
This page focuses on the impact of Neospora caninum on cattle.
|Possible outcomes of infection|
|Abortion in cattle herd|
Abortion due to Neospora usually occurs between months 4-7 of gestation, but may occur from 3 months to term. Foetuses aborted before 3 months may not be observed, so the role of Neospora at this stage of gestation is not known. Infected calves may be born showing incoordination and paralysis of the limbs but this is uncommon. Adult cows have no clinical signs of illness following infection.
Within a herd, abortion due to Neospora can be sporadic (low numbers of abortion occasionally) or it may occur as an abortion storm (large number of animals abort within a short period of time) which could be as much as 33 per cent of the breeding herd aborting within a few months.
Whether or not an abortion will occur in an infected animal is determined by a number of factors (i.e. the virulence of the strain, the health status and genetic susceptibility of the host and stage of pregnancy when infected.)In a 2011 study, it was shown that there is a 3-4 times increase in risk of abortion in infected dairy cattle compared to those that are not infected. A recent research has shown that there is no significant difference in reproduction performance between infected and uninfected beef herds.
Some properties may have more than half their cattle infected with the parasite and never encounter any reproductive problems, and then experience an abortion storm where annual abortion rates of 15-20 per cent not uncommon. Although the triggers for these abortion storms are not known, events that suppress the cow's immune system are being investigated. (immunosuppressant toxins - which can occur in mouldy fodder - and bovine pestivirus have been suggested.)
|Sources of infection|
The egg producing stage of the life-cycle of Neospora caninum occurs in the intestine of wild or domestic dogs. Eggs passed in the faeces of dogs may be ingested by an intermediate host, such as cattle. When the foetal membranes or aborted foetus are eaten by dogs, the parasite will infect the dogs which in turn shed eggs and the lifecycle is complete.
It has yet to be investigated whether congenitally infected pups produce eggs or a dog is capable of gaining a second infection after the first one has cleared.
There are two major ways of transmission for cattle. The first is from dog to cow (horizontal) via ingestion of dog faeces. Such infection of a non pregnant cow results in immunity and will not affect reproductive performance. However, if the cow is infected during pregnancy, the calf will be infected.The second route of infection is from cow to calf (vertical) during pregnancy. Such calves, if not aborted, are mostly born clinically normal but infected (persistently infected) and will have a 95 per cent chance of giving birth to infected progeny without a 'dog to cow' route being involved at all.
It is highly unlikely that the parasite is transmitted by contact, sexually or through the milk.It has been shown that vertical transmission, especially from the persistently infected cattle is the major route of infection and cycling of the parasite within herds. Recent research demonstrated there was evidence of low rates of dog to cow transmission at 70 percent of the groups.
Diagnosis of a Neospora abortion is best made by a veterinary laboratory through the examination of the aborted foetus for microscopic lesions. It is important to collect aborted foetuses, chill them (not freeze them) and submit them to the laboratory as soon as possible. (to avoid leptospirosis and Q fever, use protective gloves, seal in plastic bags and refrigerate.) A test is available through Biosecurity Queensland for the detection of antibodies in blood but this should be conducted as part of a strategic sampling of the herd.
Firm control recommendations are difficult to make as the full biology of this parasite in Australia is not known. However, where practical, you should limit the access of farm and wild dogs to infectious material, such as aborted foetuses, stillborn calves and afterbirth, and prevent exposure of dog faeces to pastures and stored feed. (This is also advisable for hydatid control.)
It should be noted that even afterbirth from non-aborting animals may contain parasites that are infectious to dogs and cattle. Thus, you should clean up afterbirth if possible.
It is important to note that controlling 'dog to cow' transmission alone is not effective enough. Reducing wild dog population in extensive grazing situations may reduce the dog to cow infection rate and the infrequent incidence of increased abortions, but it is unlikely to reduce the prevalence of infection as transmission is mainly from cow to calf during pregnancy.
On properties with a low rate of horizontal transmission, it may be possible to breed the parasite out of a herd by not including infected cows in the breeding herd, or on dairy farms by not breeding replacement heifers from infected cows. A blood test can help determine which animals are infected, and may be especially useful for studs and pre-purchase testing.
A vaccine is currently available in the United States. However, the vaccine was not capable preventing vertical transmission of Neospora in cattle and its effectiveness in preventing abortions is still under review. Such a vaccine, if shown to be effective, would not be available in Australia for several years.
As research progresses, clearer prevention and control strategies should be developed. Work by the University of Queensland has shown that the genetics of valuable animals can be salvaged by transferring embryos from infected animals into uninfected recipients. At present, no drug therapy is available to treat or control Neospora.