Paramyxovirus Type 1

Its Importance for the Commercial Poultry Industry.  Pigeon Paramyxovirus type 1 is closely related to Newcastle
Disease virus (NDV), as they are both classified in the same family of
viruses, Paramyxoviridae, and are within the same serotype, referred to
as Paramyxovirus type 1.

Pigeon Paramyxovirus type 1 (PPMV-1) is closely related to Newcastle Disease virus (NDV), as they are both classified in the same family of viruses, Paramyxoviridae, and are within the same serotype, referred to as Paramyxovirus type 1. In spite of their close relationship, there are clear antigenic (antibody stimulating) differences between NDV and PPMV-1, which can only be determined by laboratory testing.

Newcastle disease viruses differ considerably in their ability to cause disease in various species of birds and have been described as avirulent (causing no clinical signs), low pathogenic (causing only mild to moderate clinical signs) and virulent (highly pathogenic viruses causing “Exotic Newcastle disease”).

On the other hand, the PPMV-1 have been isolated from many outbreaks in commercial and feral pigeons throughout the world with increased mortality and severe clinical signs.

Differentiation of PPMV-1 and virulent NDV is important as the virulent strains result in an extremely contagious disease (Exotic Newcastle disease) that can infect more than 236 avian species, causing very high mortality in susceptible hosts such as chickens and turkeys. Among various NDV outbreaks, only those caused by virulent strains must be reported to the OIE (Office International des Epizooties) by its member countries.

Exotic Newcastle disease is a reportable disease in Canada and the CFIA takes aggressive actions against it. Occurrence of a virulent form of NDV may also impose trade restrictions depending on the affected species and potential epidemiological links.

PPMV-1 was isolated for the first time from pigeons in the Middle East in late 1970s and subsequently was introduced throughout North Africa. The virus was reported in Italy in 1981 and from 1981 to 1984, spread throughout the world. PPMV-1 has been isolated from pigeons, doves and ornamental birds in addition to commercial and feral pigeons. It has been suggested that PPMV-1 is a variant form of NDV of chickens and possibly emerged as a result of frequent transmission of the virus from chickens to pigeons.

Confirmed cases of PPMV-1 were first reported in the United States (U.S.) in 1984 and since then there have been numerous reports of PPMV-1 isolations from feral and commercial pigeons across the U.S. During November 2006, a significant increase in the number of isolations of PPMV-1 from commercial pigeon operations with nervous signs and increased mortality were reported in Canada. 

PPMV-1 and poultry 
In 1984, a number of outbreaks in commercial poultry flocks in the U.K., with clinical signs such as drop in egg production, nervous signs and increased mortality were attributed to infection with PPMV-1. Contamination of feed with pigeon feces and carcasses was considered the main source of most of these outbreaks.

Despite widespread outbreaks of PPMV-1 in feral and commercial pigeons in the U.S. since 1984 and recently in commercial pigeons in Canada, so far, there have been no confirmed reports of this virus causing obvious clinical disease in commercial poultry flocks in these countries. However, in 2001, it was speculated that a case of egg production drop in a commercial layer flock in the U.S. was attributed to the contamination of the feed ingredients with infected pigeon carcasses (PPMV-1 was isolated from the pigeon carcasses but not from the layer flock), although this was never proven.

Because of historical evidence that demonstrates the ability of some pigeon-origin isolates of PPMV1 to cause clinical disease in commercial poultry flocks in other parts of the world (e.g., Europe, 1984), there is concern that these viruses might spread from pigeons to commercial poultry flocks and cause clinical disease. There have been a number of studies in the U.S. that have assessed the virulence of pigeon-origin PPMV-1 isolations in chickens under experimental conditions.

The results of these studies have indicated that various isolates of the PPMV-1 have shown different levels of pathogenicity (virulence) for chickens, ranging from no disease or mild respiratory signs (sneezing) to extreme cases of high mortality in chicks inoculated at one day of age. Inoculation of chickens at older ages with the same isolates resulted in milder clinical signs. The overall results indicate that PPMV-1 isolates, and/or age of the chicken at the time of inoculation are important factors in determining the absence or extent of observed clinical signs. One recent study showed that dual experimental infection of chickens with PPMV-1 isolates and other agents such as IBDV (Infectious Bursal Disease virus), CAV (Chicken Anaemia virus) and MG (Mycoplasma gallisepticum) did not aggravate clinical signs of PPMV-1.

It is important to note that PPMV-1 is typically very contagious and can spread from infected pigeon operations to other pigeons or commercial poultry flocks, especially with inadequate biosecurity measures. Also, it is possible that chickens could get infected with PPMV-1 and shed the virus in the absence of clinical signs.

The possibility of frequent transmission of PPMV-1 to domestic poultry flocks has also raised some concern. This is based on the fact that under experimental conditions it has been shown that when series of chickens were inoculated sequentially (serial passage), the ability of these viruses to cause disease in chickens have shown to be increased. It is not known if PPMV-1 can gain increased disease capability, if allowed to circulate in commercial poultry flocks but this possibility certainly demands careful investigation. Careful attention is  warranted to avoid any direct and indirect contact between infected pigeon operations and commercial poultry flocks.

Can Pigeons Get Infected With Virulent NDV?
Similar to many other avian species, pigeons are considered susceptible to virulent strains of NDV and can become infected, shed the virus and potentially infect other pigeons and poultry flocks. In countries where Exotic NDV is not  present, clinical cases of pigeons with nervous signs should be carefully investigated to ensure that they are not infected with virulent (Exotic) NDV. This can only be done with laboratory testing, which can be facilitated by a veterinarian.

What Can Be Done to REduce the Risks?
To summarize, the PPMV-1 that has been increasingly isolated from pigeon operations in Canada demands monitoring and appropriate measures for two main reasons: 1) These viruses are able to cause disease and mortality in non-vaccinated pigeons and result in losses to these operations. 2) If adequate biosecurity is not in place, there is a potential to spread to commercial chicken and turkey flocks. Even if the infection with the PPMV-1 isolates in commercial poultry flocks is not causing overt clinical signs, it may provide an opportunity for the virus to circulate in these flocks for an extended period of time and based on available experimental studies, potentially gain more ability to cause clinical signs and disease in commercial poultry flocks in the future. The potential for this to happen under field conditions is not known. n

References are available upon request from the Poultry Industry Council. This article is available as a factsheet (number 158) from the PIC website (www.poultryindustrycouncil.ca) and was edited by Research Co-ordinator Kimberly Sheppard.