Derzsy's disease

Goose parvovirus infection occurs in all breeds of domestic geese and Muscovy ducks. The disease has also been reported in wild geese following accidental infection (Schettler, 1971). Muscovy duck parvovirus infection has been reported to occur in various genetic crosses of Muscovy ducks and several indigenous breeds of waterfowl in the Far East. Geese seem to be less susceptible to Muscovy duck parvovirus than to goose parvovirus. In both geese and Muscovy ducks the disease is strictly age dependant with up to 100% mortality occurring in birds under one-week of age. Progressive resistance to infection occurs so that by the time the birds are 4 to 5-weeks-old negligible losses occur. Following infection, older geese and Muscovy ducks show no clinical signs but respond antigenically. Other breeds of waterfowl and domestic poultry seem to be refractory to infection.

Derzsy's disease has been reported from all the major goose and Muscovy duck farming countries of Europe, including the former USSR, and Israel. The disease has also been reported from China, Taiwan, Vietnam and Japan. In countries such as France and Germany, where geese and Muscovy ducks are farmed intensively, the disease has caused serious economic problems.

Isolation and Identification of the Causative Agent

A variety of methods have been developed and evaluated for the diagnosis of goose parvovirus infection (Gough, 1997;1998). The virus can be isolated from a variety of suitable postmortem specimens following inoculation of 10 to 15-day-old embryonated goose or Muscovy duck eggs via the allantoic cavity. Embryo mortality occurs 5-10 days post-inoculation with haemorrhages and ochre-coloured livers. The virus can also be isolated in primary cell cultures of goose or Muscovy duck embryos. Isolation of the virus is facilitated by inoculating cultures before they reach confluency. The virus produces a well-defined cytopathic effect (CPE) three to five days post-infection. In haemotoxylin and eosin-stained preparations Cowdrey type A intranuclear inclusions and syncytium formation are often present. Electron microscopic examination of infected cell cultures or neutralization with specific goose parvovirus antiserum can confirm the presence of the virus.

Immunofluorescence has also been used to detect the presence of antigen in both goose embryos and infected cell cultures. Other methods of detecting goose parvovirus have been developed, including the immunoperoxidase technique and reverse indirect haemagglutination test.

An agar gel diffusion technique has been described using hyperimmune rabbit anti-goose parvovirus serum to precipitate parvovirus in allantoic fluid from infected goose embryos. Aggregates of goose parvovirus virions have also been detected by electron microscopic examination of ultra-thin sections of heart and bursa of Fabricius from infected goslings, and in concentrated extracts of faeces from goslings showing clinical signs of goose parvovirus.

A polymerase chain reaction (PCR) has been developed to detect parvoviruses. Primers have been designed from conserved regions of the VP1 and 2 genes that encode for the capsid proteins. These can be used to differentiate strains of goose and Muscovy duck parvovirus following restriction fragment length polymorphism (RFLP) analysis.

Serology

Confirmation of goose parvovirus infection can be obtained by serological means. The most commonly used method is the virus neutralization test in embryonated goose or Muscovy duck eggs or primary cell cultures to detect the presence of goose parvovirus neutralizing antibodies. A neutralization test has also been developed for use in Khaki Campbell or Pekin duck eggs using a duck-embryo-adapted goose parvovirus. Though less sensitive than the neutralization test, the agar gel diffusion test is a useful method of rapidly testing large numbers of sera for the presence of goose parvovirus antibodies. Other serological techniques developed include the spermagglutination-inhibition and ELISA tests. Antigen for these tests is readily prepared from allantoic fluid of infected goose eggs by means of polyethylene glycol (PEG) concentration of the virus.

Apart from duck herpesvirus enteritis there are no other known viral infections that cause high mortality in young geese or Muscovy ducklings. However, equivocal results can arise when viruses other than parvovirus are isolated, particularly reoviruses and adenoviruses. In such cases it may be necessary to carry out serological tests in order to confirm the diagnosis.

The subject has been reviewed in detail elsewhere (Gough, 1997). There is no specific treatment for goose parvovirus infection. Antibiotic therapy has been used to reduce losses from secondary bacterial or fungal infections. Because many outbreaks of goose parvovirus are directly attributed to transmission of the disease by congenitally infected goslings during hatching, the practice of incubating and hatching eggs that have originated from different breeding flocks should be discouraged. Only eggs from known parvovirus-free flocks should be incubated together and good hatchery hygiene should be maintained.

On farms where outbreaks of the disease have occurred, the practice of breeding from geese that have survived the disease as goslings should also be discouraged, as these birds are potential carriers of the virus. All contact geese whether goslings or adults, should be serologically tested in order to identify which birds have been infected horizontally. Positive reactors should be removed from the flock, as these birds may also become carriers of the virus.

As the disease is confined to young geese or Muscovy ducklings, control measures have been developed to provide adequate immunity during the first 4-5 weeks of life. Some of the early outbreaks of goose parvovirus occurring in China in 1962 were controlled by the use of hyperimmune serum in newly hatched goslings. Serum therapy was widely used when the disease subsequently appeared in Europe, using serum produced in hyperimmunized geese. However, passive immunization was found to be expensive and time-consuming, particularly as two doses of serum were often required to produce adequate immunity. Active immunization of adult breeding geese and Muscovy ducks with virulent virus has also been reported. The results showed that protection against goose parvovirus was transferred to the progeny via the egg yolk.

One of the first vaccines against the disease was developed in China, and during the period 1962 to 1979 about four million female geese were vaccinated. The virus was attenuated following multiple passage in embryonated goose eggs and a good degree of protection to challenge was recorded in the progeny goslings. Other vaccines have been developed by attenuation of the virus in goose or Muscovy duck embryo cell cultures, for use in breeding geese and goslings. Duck embryo-adapted goose parvovirus vaccines have also been shown to induce a good immune response in goslings and breeder geese.

In flocks of geese where parvovirus has not been diagnosed, inactivated vaccines have been used prophylactically.