Egg transmission of egg drop syndrome 1976 virus in fowl

An avian influenza virus H6N1 outbreak in commercial layers: case report and reproduction of the disease

An outbreak of low pathogenic avian influenza (LPAI) subtype H6N1 (intravenous pathogenicity index = 0.11) infection occurred in four productive brown layer flocks on three farms in the Netherlands within a period of two months. The farms were located at a maximum distance of 4.6 km from each other. The infections were associated with egg production drops up to 74%, pale eggshells and persisting high mortality up to 3.2% per week. Three flocks were slaughtered prematurely as they were not profitable anymore. Newcastle disease, infectious bronchitis, egg drop syndrome and Mycoplasma gallisepticum infections could very likely be excluded as cause of or contributor to the condition in the field. Also, the anticoccidial drug nicarbazin, which can cause egg production drops and eggshell decolouration, was not detected in eggs from affected flocks. Furthermore, post mortem examinations revealed no lesions indicative of bacterial infection. Moreover, bacteriological analysis of hens was negative. The condition was reproduced in commercial brown layers after intratracheal inoculation with virus isolates from affected flocks. It is concluded that the LPAI H6N1 virus is very likely the only cause of the disease. An overview of main manuscripts published since 1976 describing non-H5 and non-H7 avian influenza (AI) virus infections in chickens and their biological significance is included in the present study, in which once more is shown that not only high pathogenic AI virus subtypes H5 and H7 can be detrimental to flocks of productive layers, but also non-H5 and non-H7 LPAI viruses (H6N1 virus). RESEARCH HIGHLIGHTS LPAI H6N1 can be detrimental to productive layers Detrimental effects are severe egg drop and persistent high mortality LPAI H6N1 virus outbreak seems to be self-limiting.

Studies on the persistence and excretion of egg drop syndrome 1976 virus in chickens

EDS virus strain 127 did not induce clinical signs or gross lesions in susceptible chicks of various age groups and in adult cocks. Virus persistence in various internal organs and the rate of excretion of virus by experimentally-infected chicken declined rapidly with increasing age. Virus 127 was detectable in organs of young chicks up to 5 weeks post-infection and in their faeces up to 2 weeks post-infection. In adult birds virus 127 persisted in tissues for about 3 weeks and was excreted with faeces for only 1 week post-infection. Vaccination of adult cocks with an inactivated vaccine resulted in intermittent shedding of virus only within the first 4 days post-challenge; thus, in comparison to non-vaccinated chickens, vaccination reduced virus excretion in faeces to a major extent.

Biochemical changes in blood and uterine fluid of fowl following experimental EDS'76 virus infection

The pH, pCO2, and pO2 values and the concentrations of sodium, potassium, calcium, magnesium, chloride, phosphorus, bicarbonate, base excess, protein, glucose, as well as the activity of alkaline phosphatase and malate dehydrogenase were determined in the venous blood and uterine fluid of control and EDS'76 virus-infected fowl. Moreover, the pH of the mucosa of different parts of the oviduct was measured. Hens were examined in the period from 10 to 24 days following infection; blood and uterine fluid samples were collected approximately 14 hours after oviposition, provided a plumped egg was present in the uterus. Examination of blood and pH measurement of oviduct mucosa did not yield significant differences between infected and noninfected hens. In comparison with noninfected control birds, the mean sodium concentration of the uterine fluid of infected hens producing soft shelled or shell-less eggs had evidently increased, while the mean concentration of potassium, calcium, magnesium and glucose had decreased. Similar differences were also observed between infected hens producing normally shelled eggs and infected hens producing abnormally shelled eggs. No significant differences between infected and not infected hens were observed concerning the other values determined in the uterine fluid. It is concluded that functional disturbances which account for shell aberrations following EDS'76 virus infection are located in the surface epithelial cells of the uterine mucosa. These disturbances are very probably initiated by a depressed function of the sodium pump. All changes observed in the uterine fluid of infected hens could be explained by this depressed function.

Serological examination and egg production of progeny of fowl experimentally infected with egg drop syndrome 1976 virus

Following EDS'76 virus (BC14 virus) infection of breeder chickens by the conjunctival route, vertical transmission occurred in the first week after infection. In the progeny which had been infected with EDS'76 virus by the vertical route, increasing haemagglutination inhibiting (HI) titres to BC14 virus and increasing numbers of birds with HI titres were observed from 3 weeks to 15 weeks of age. Sixty-one per cent of the hens and 77 per cent of the cocks had 2 log HI BC14 virus titres exceeding 4 at an age of 15 weeks. Some birds which han been serologically negative throughout the rearing period, seroconverted between 25 and 28 weeks of age. This phenomenon occurred in hens as well as in cocks. Simulation of stress twice during the laying period by injection of corticosteroid hormone did not increase the number of birds serologically positive to EDS'76 virus. EDS'76 was observed in the group of hens that was vertically infected, since egg production was significantly depressed between 28 and 34 weeks of age. Probably this was mainly the results of a production drop in the hens showing serconversion at 27 or 28 weeks of age. In this group of fowl vertically infected with EDs'76 virus, serologically positive birds appeared to be protected for the greater part to BC14 virus challenge at 50 weeks of age, while negative birds seemed to be fully susceptible. Chicks hatched from eggs collected in the third and fourth week after infection of the dams had maternal antibodies. Fertility and hatchability of apparently normally shelled eggs seemed not to be affected after BC14 virus infection of the dams. Intensive contact with contaminated faeces is probably an indispensable condition for lateral transmission of the virus.

Incidence of EDS'76 virus infection in fowl in 1980 in the Netherlands in comparison with the incidence in 1976-1978

Serological examinations demonstrated that Egg Drop Syndrome 1976 (EDS'76) virus infection was of no significance in the Dutch poultry industry in 1980, in contrast to the situation in 1976-1978 when this infection was of widespread occurrence. The conclusion was reached that the sharp decrease in the incidence of EDS'76 virus infection was due to large scale vaccination in 1978 and 1979. The results of this study show that there is no further need for general EDS'76 vaccinations. However, continuous serological monitoring is necessary to detect flocks for which vaccination is indicated.