In vivo interference between pathogenic and non-pathogenic viruses.

The interference among viruses is a well-documented biological phenomenon, both in animals and tissue culture systems. In two of our previous in vivo experiments and in four independent animal experiments, which are described in this presentation, interferences were successfully used to influence the outcomes of viral diseases by using non-pathogenic viruses. In this study, four pathogenic viruses were studied in their natural hosts, and against these viruses, in different combinations, 15 non-pathogenic viruses were tested. There was great variation in mutual effects among pathogenic and non-pathogenic viruses. In our four experiments, the viruses were either simultaneously inoculated or the non-pathogenic viruses were preinoculated. Newcastle disease vaccine (Strain H) had remarkable effects in the development of mouse ascites-associated lymphoma virus. The 50% mortality rate in mice caused by a vaccine strain of rabies virus was reduced to 15% using avian encephalitis virus. The clinical manifestations of rabbit myxoma virus effects were significantly delayed by Newcastle disease vaccine (Strain H). The 72% mortality rate due to Rous sarcoma virus in chickens was decreased to 33.3% when the animals were preinoculated with avian bursa virus vaccine.

The role of wild birds in the spread of influenza viruses.

Eggs deposited by different migrating wild bird species in pond farm areas in Hungary were examined for yolk antibodies to different variants of human A/H3N2 influenza virus. Antibodies to Victoria/75 and Texas/77 occurred in 17.9 and 32.0% of gull eggs, and 5.6 and 16.4% of common tern eggs, respectively, while antibodies to A/H1N1/77 occurred in roughly similar proportions (10.2 and 13.4%) in the eggs of both species. Infection of the gull and tern populations of given areas by human and avian influenza A viruses differed greatly in two consecutive hatching periods. While in 1978 7.6 and 1.1% of the gull and tern eggs, respectively, contained antibodies to the avian subtype Havl, no such antibodies were found in 1977. Subtype A/H3N2/Texas/77 virus was isolated from adult gulls and 1-3 weeks old gull chicks, and subtype H1N1 virus from mallard ducks. Three months before the onset of the Texas/77 epidemic, 95% of SPF chickens, and 71-81% of chickens hatched 3 months after termination of the A/H1N1/77 epidemic, had had HI, VN and SRH antibodies to the Texas/77 strain and A/H1N1/77 strains, respectively.

Susceptibility of birds to type-B influenza virus.

Among Zoo birds and migrating wild birds examined serologically during an outbreak due to influenza B virus, 4.1% were found to have serum antibodies to the agent. Evidence of avian susceptibility to the agent was emerging from reisolations of the virus and primary and secondary HI antibody response of the birds in subsequent infection experiments performed on adult pheasants and mallards, as well as one-day-old domestic ducklings and chicks. The virus persisted in the pheasants for at least three weeks, and adult pheasants, mallards and domestic ducklings were found to transmit it by contact to part of their susceptible mates.

Direct isolation of mycoplasmas and acholeplasmas from sera and kidneys of calves.

Kidneys and sera of calves from various farms and primary kidney tissue cultures were tested for mycoplasma and acholeplasma contamination. Altogether 24 strains belonging to Mycoplasma arginini and Acholeplasma axanthum were isolated from tissue cultures, kidneys and sera. The same species were detected from lungs and peribronchial lymph nodes of calves, together with A. laidlawii, A. modicum and M. bovirhinis species. There was a close correlation between the mycoplasma content of tissue cultures, sera and kidneys and the clinical picture observed in the farm, as well as between the quality of tissue cultures and the mycoplasma content of organs, sera and tissue cultures.

Studies on the pathogenicity of Acholeplasma axanthum in swine.

Acholeplasma axanthum sp. was isolated from the lung of swine with catarrhal pneumonia. Clinical symptoms of respiratory disease, gross and histological lesions of pneumonia, as well as serological response were produced by intranasal inoculation of ;miniature pigs' with the supernatant of lung suspension containing Acholeplasma axanthum and by a 48 hr. broth culture of the strain.A similar picture of disease was observed in animals held in contact with the animals inoculated with untreated lung suspension. Acholeplasma axanthum was isolated from the nasal cavity, lung and peribronchial lymph nodes 7-41 days after inoculation. No lesions were observed after inoculation of pigs with the supernatant of lung suspension pretreated with oxytetracycline or chloroform, and no successful isolation of Acholeplasma axanthum could be achieved after this treatment.