[Isolation from ducks of a hypervirulent strain of duck plague virus and an avian type 6 paramyxovirus]. / Isolement chez des canards mulards d'une souche hypervirulente de virus de la Peste du canard et d'un Paramyxovirus aviaire de type 6.

This paper describes the isolation and identification of a duck plague virus (DP) and a paramyxovirus (PMV6), from the livers and intestines collected in 4-month old mule ducks, under fattening, exhibiting 75% mortality and necrotic-haemorrhagic gross lesions. These viruses were isolated in specific pathogen free (SPF) muscovy duck eggs and SPF chicken eggs respectively. Then the DP virus was adapted to duck and chicken fibroblasts. The disease was reproduced in 2-week old SPF muscovy ducklings, intramuscularly inoculated with the previous organs, as well as in contact ducks. From them, only the DP virus was isolated again. Experimentally the intramuscular inoculation of the duck plague French vaccinal strain, 4 h post contact, did not prevent the disease and did not decrease its severity. Regarding the DP virus, the typical signs and lesions observed in experimentally infected muscovy ducks as well as the presence of intranuclear inclusions of the epithelial cells of their oesophagus, intestines, bursa of Fabricius and liver on the one hand, and on the other hand, of the epithelial cells of the duck egg chorio-allantoic membrane and fibroblasts inoculated with the samples first defined, allowed the characterization of the virus. Direct electron microscopy, as well as the results of seroneutralization tests with different specific avian Herpes virus antisera confirmed the DP virus identification. Moreover the DP isolate was not antigenically different from the serotype actually known. The haemagglutinating virus (PMV6) was characterized by direct electron microscopy as well as with 18 specific avian Myxovirus antisera; its identification was confirmed too by the specific seroconversion observed 4 weeks post-inoculation of this virus, in 11 weeks old SPF muscovy ducklings. Finally an assay was carried out to appreciate the pathogenicity of theses viruses inoculated either separately or associated. It showed the high pathogenicity of the DP strain. The PMV6 was apathogenic and no synergic effect with the DP virus was demonstrated. It appears to be the first isolation of PMV6 in France, to our knowledge. The epidemiological circumstances related to theses isolations are discussed. The failure of the emergency vaccination in contact ducks, might be attributed to the high virulence of the DP strain.