Pathogenicity Of Newcastle Disease Virus In Ducks

ND (Newcastle disease, ND) was an acute, highly contagious disease which caused by Newcastle disease virus (NDV). NDV can infect a variety of birds with high death. Newcastle disease virus (NDV) host almost include all kinds of the bird. For the traditional view, the waterfowl are considered to be the original host of NDV and can be infected in a latent way. But since 1997, the emergence of gene type VII NDV, have led to geese and ducks infected with the disease, showed that the pathogenicity host of NDV are expanding. At the same time, Class I , genotype VII, genotypeâ…¡NDV have been isolated from seemed a healthy wild waterfowl all around the world, which made waterfowl role in Newcastle disease virus evolution and spread receive attention again. Mallards were standard species in the wild waterfowl and the ancestor of other ducks other than Muscovy duck. It may be helpful to analysis the role of mallard in NDV transmission and evolution through the study of different genotypes of NDV?s pathogenic and replication characteristic.In this study, SPF Shao ducks and mallards as animal infection model for studying the pathogenicity of Newcastle disease virus. The standard virulent strain F₄₈E₉, vaccine strain LaSota, genotype VII of wild mallard type NDV Mallard/CH/HLJ363/05 (WB-363) and duck virus Md / CH / GD/1/05 (Md) were selected for the study. With different doses and inoculated way of virus infect duck to observe the incidence of mortality and collect throat and cloacal swabs to isolate the virus. to determine if the duck release virus and release time; The tissue distribution of important organs , serum neutralizing antibody and seroconversion were detected 4-5 days post infection. Meanwhile, the pathogenicity to cohabitation ducks or chickens were established.The results showed that there is no morbidity and no mortality post vaccine strain La Sota inoculated Shao ducks and mallards in different doses by intranasal way of natural infection, eye and muscle, intravenous inoculation. Collected the throat and cloacal swabs for testing, only Shao duck virus attack group after the high dose group showed a transient virus release only 3 days after virus attack, but there is no morbidity and no mortality, and a weak seroconversion. Necropsy experimental ducks, monitored for 4-week there is no virus replication in the main organs, and seroconversion rates and neutralizing antibody titer are low.Isolated from wild birds and ducks in the two genetic strains of Newcastle disease virus type VII Mallard/CH/HLJ363/05 and Md/CH/GD/1/05 in simulated natural way to duck under the experimental infection, at the highest dose 10^8.6EID₅₀/0.2ml and lowest dose 10^6.6EID₅₀/0.2ml group, it can not lead to morbidity and mortality of ducks, but some ducks can detect of virus release; By muscle, intravenous injection with WB363 strain can be lethal to ducks, live ducks produce significant seroconversion, which is higher than La Sota vaccine strain. The virus can be isolated from swab samples and main organs by muscular, intravenous way with gene type VII virus. Virus can replicate in the duck. There are short time of virus release with the experimental duck, and all the cohabited ducks were no virus release, morbidity and mortality, and serum antibody titers less than 1:4, but kept together with the infected ducks, the cohabitation chickens died. F₄₈E₉ standard strain in intranasally and eye way, the 15 days Shao duck can be infected with 10^2.8EID₅₀/0.2ml, and death in 10^5.8EID₅₀/0.2ml. With the same dose of virus to mallards, there are no morbidity, mortality, only latent carriers of the virus. Mallards inoculated with F₄₈E₉ strain in intramuscular and intravenous way can be infected, the virus can replicated in many kinds of organ. Cohabitation mallard group can produce neutralizing antibodies, but no virus release, morbidity, mortality. 1 month old mallards have a certain resistance to F₄₈E₉, the virus can not be effective replicate in vivo of duck.Preliminary results show the widely used vaccine La Sota strain that immunized in chicken can not replicate efficiently in vivo of Shao ducks and mallards, so it is not suitable to use as a candidate vaccine for Newcastle disease. Pathogenic characters of F₄₈E₉ strains are higher than the current popular gene VII type NDV, but they can be replicated in vivo in the duck in a latent way and has a potential impact on mutation and spread of NDV. Wild mallard ducks resistance ability is higher than domestic duck and affected by age.