Paramyxovirus: Eliminating the confusion
The paramyxovirus that infects birds belongs to the family Paramyxoviridae. At least nine distinct serotypes have been identified with several additional isolates from birds awaiting characterization. The most important paramyxovirus that infects birds is PMV-1, commonly know as Newcastle Disease (NDV). This serotype is globally distributed and all species of birds are susceptible to it. Pigeon Paramyxovirus-1 (Pigeon PMV-1) is also distributed world-wide and can cause disease in racing, homing and show pigeons and potentially birds of prey that eat the infected bird.
There are four groupings of PMV-1 based upon their virulence and type of infections they induce in chickens: Lentogenic may cause mild or unapparent disease; Mesogenic, or moderate severity of disease; Velogenic Neurotropic stains (VNND) causing severe disease with high mortality; and Velogenic Viscerotropic strains(VVND) causing severe disease and mortality with hemorrhage within the intestinal tract. The term Exotic Newcastle Disease (END) is VVND or VNND. The lentogenic and mesogenic form is very widespread in the avian species, but usually does not cause deadly disease outbreaks. The velogenic strains are considered foreign pathogens that do not naturally occur in the USA. Birds being brought to the USA illegally are generally the source of infection with END. Globally, many countries have disease outbreaks of END, affecting several species of birds, including birds of prey.
In general, clinical signs with PMV-1 include gastrointestinal and respiratory disease. As the disease progresses, central nervous system (CNS) signs (ataxia, torticollis, opisthotonos and convulsions) become apparent. The response to disease is affected by the strain of the virus, age, species, and condition of the bird. It is important to remember that a strain of paramyxovirus causing severe clinical disease in one group of birds may only cause subclinical infections in others. It has been noted that vultures and owls may be more resistant to infection with NDV.
Transmission of this virus is usually by direct contact, air-borne routes, and vectors. Infected birds may shed the virus in their feces and through the respiratory tract. This virus can survive for several weeks in the environment, especially with cool damp weather. This is often why we will see outbreaks in the winter months. The virus is present in all parts of the carcass of an infected bird and when introduced into a susceptible flock, all birds may be infected within 2-6 days. The detrimental effects on the poultry industry by this disease require any outbreak to be reported to the World Organisation for Animal health (OIE). Outbreaks affect the ability of states or countries to export poultry products until the outbreak is over and the poultry considered clean of infection. In the United States in order to control the spread of this disease, the following takes place: Strict isolation or quarantine of outbreaks; humane destruction of all infected and exposed birds; thorough cleaning and disinfection of the premises; proper carcass disposal; pest control in flocks; depopulation followed by 21 days without poultry before restocking; avoidance of contact with birds of unknown health status and control of access to poultry farms.
The goal of any vaccine is to prevent clinical disease and reduce or abolish virus shedding. Inactivated and live attenuated NDV vaccines can prevent clinical disease but not virus shedding especially following a virus challenge. Currently research utilizing recombinant DNA technology is the platform for developing more efficient vaccines. Recombinant, genotype-matched, live attenuated vaccines generated by reverse genetics is showing the most promise for a novel vaccine that may outshine all the currently available NDV vaccines. NDV vaccines are designed for the poultry industry. They have been used in other species including birds of prey, but detailed and ongoing research to evaluate their efficacy is still needed. Depending on in which country you reside, there may be limitations of what vaccines are available for your use.
Pigeon Paramyxovirus 1 (Pigeon PMV-1)
This serotype of paramyxovirus is distributed worldwide. This serotype in poultry is considered mesogenic but often causes severe neurologic disease and mortality, especially in young pigeons. Pigeon PMV-1 may occur year round but is common in unvaccinated pigeon flocks during the racing seasons. This virus can be transmitted through direct contact or indirect contact with infected birds through contaminated respiratory secretions or feces. Infected birds may shed this virus for up to a month and the virus has the ability to remain infectious in contaminated feces for months.
The clinical signs are very similar to PMV-1 with the addition of kidney involvement. Infected birds can be successfully treated with strong supportive care and isolation from the flock for 6-8 weeks following clinical signs. This will prevent exposure to virus shed from the infected pigeon to the rest of the flock. There are strong vaccination programs for pigeon flocks to help control this virus. Birds of prey are susceptible to this virus and can become infected by Pigeon PMV-1 by eating infected prey or being in close proximity to inhaled infected respiratory secretions or feces.
There are several pigeon PMV-1 vaccines available depending on your country of residence. Most of these vaccines are a killed vaccine. In some countries a chicken NDV vaccine is available for “off label” use in the pigeon. It is believed that the chicken vaccine may provide cross protection against pigeon PMV-1. There is concern that if a new strain of pigeon PMV-1 develops, the current vaccines will not be protective.
Paramyxovirus in birds of prey
Birds of prey can be highly susceptible to NDV depending on the species. Falcons, hawks and eagles can become infected, remain asymptomatic, die following a brief period of lethargy, anorexia and diarrhea, or become neurologic and die. Owls and vultures in general may exhibit resistance to disease but have the ability to shed the virus. Pigeon paramyxovirus -1 can also be infectious to birds of prey as mentioned above. Clinical signs vary and follow the same path as in NDV or pigeon PMV-1. Birds may recover if aggressive supportive care is provided and the neurologic form does not progress.
There is no specific bird of prey vaccination for any paramyxovirus strains. In areas where NDV or pigeon paramyxovirus is prevalent, inactivated chicken-based or pigeon-based vaccines have been used. Several studies from the Middle East support the use of chicken NDV vaccines to control NDV outbreaks in the falcons. This may offer some cross protection against pigeon PMV-1; however, research is needed to evaluate the efficacy of the vaccination program.
The following are examples of the many types NDV testing available. The difficulty in testing any bird for paramyxovirus is what strain is present and how sensitive and reliable are the results. Research is ongoing to find the most complete and foolproof test.
is regarded as the gold standard method for the definitive diagnosis of NDV and is often used for validating the results from other detection methods.
HI (hemagglutination inhibition) measures titers of the NDV antibodies. HI titers can be monitored in a vaccinated bird and a sudden rise in the titer may indicate exposure to a field strain of NDV.
The ELIZA test is a serology test utilizing detection of the virus antigen. This type of testing may be able to differentiate antibodies due to vaccination from those due to infection. Limitations do exist with this type of testing; however, ELIZA testing can be useful for surveillance.
Virus neutralization test (VNT) is particularly useful in measuring NDV specific neutralizing antibodies. This test is better suited in the assessment of vaccine protective immunity than in NDV surveillance.
Molecular Based Assays
Reverse Transcription-Polymerase Chain Reaction (RT-PCR), QuantitativePolymerase Chain Reaction (qPCR) and Non-PCR Amplification Techniques are all involved with detection and identification of the virus genome. The virus primers used in these tests must be constantly updated to identify mutations of the virus.
Next-generation sequencing (NGS)
NGS is revolutionizing the diagnosis of infectious diseases. This technique is facilitating a rapid, sensitive, and specific detection and differentiation of viruses. This technique is often used to determine what strain of paramyxovirus is present or if a new novel virus is present.
Newcastle Disease in Falcons in Saudi Arabia; Jamie Samour
Development of a RT-nested PCR test detecting pigeon Paramyxovirus-1 directly from organs of infected animals; C Barbezange
Diagnostic and Vaccination Approaches for Newcastle Disease Virus in Poultry: The Current and Emerging Perspectives; Muhammad Bashir Bello