Page 374 - Avian Virology: Current Research and Future Trends

Avian Pox Viruses

Deoki N. Tripathy* 13

Department of Pathobiology, College of Veterinary Medicine, University of Illinois, IL, USA

*Correspondence: sreddy@cvm.tamu.edu
https://doi.org/10.21775/9781912530106.13

Abstract the genus. Synonyms, which have been used for avian pox virus
Avian pox viruses infect both wild and domestic birds. In this infections, are: contagious epithelioma, avian diphtheria; variole
regard, more information is available on fowlpox virus type species aviaire (French); Geflugelpocken (German); bouba aviaria (Por-
of the genus Avipoxvirus because of its economic impact on com- tuguese); virula aviar, difteria aviar (Spanish). The disease has
mercial poultry. Canarypox virus infection causes high mortality worldwide distribution.
in canaries. The diagnosis is based on the development of cutane- Fowlpox and turkeypox are economically important diseases
ous and/or diphtheritic lesions and histopathologic examination of domestic poultry. The disease is of special significance for
of the lesions for cytoplasmic inclusions. The virus multiplies aviculturists as poxvirus infections in canaries can cause high
in the cytoplasm of infected cells and produces cytoplasmic mortality in a short time. While poxvirus infection is generally
inclusion bodies. Virus isolation is carried out in the developing manifested as either cutaneous, diphtheritic or systemic, all forms
chicken embryos. Complete nucleotide sequence of the genomes of the disease may occur in the same bird. An acute systemic form
of fowlpox virus, canarypox virus and few other avian pox viruses of the disease observed in canaries causes high mortality. All forms
has been determined. Polymerase chain reaction (PCR) is being of the disease occurring either singly or in combination have been
used to amplify nucleotide sequences of specific genes, e.g. 4b, for reported in canaries (Donnelly et al., 1984; Shivaprasad et al.,
diagnosis and phylogenetic analysis of strains. For disease preven- 2009). The ‘cutaneous form’ of the disease is characterized by
tion, vaccines of fowlpox and pigeonpox virus origin have been development of proliferative skin lesions while presence of upper
used for many years by the poultry industry. Outbreaks of fowl- digestive and respiratory tract lesions are referred as ‘diphtheritic
pox in previously vaccinated chickens still occur in many poultry form’ of the disease.
operations. The virus strains isolated from such outbreaks show
insertion of full-length reticuloendotheliosis virus (REV) in their
genome. REV has been associated with immunosuppression and Etiological agent
tumour formation. It appears that the emerging strains are anti- Because of the large size, avian pox viruses can be observed under
genically and genetically different for which the current vaccines light microscopy (Fig. 13.1). The viral particles, Borrel bodies,
do not provide adequate protection (Tripathy and Reed, 2013). within the inclusion bodies (Bollinger bodies) are the aetiological
agent (Woodruff and Goodpasture, 1929).
The virion is oval to brick shaped measuring 250 to 400 nm
Introduction (Fig. 13.2). It consists of an electron dense, centrally located
Pox is a common viral disease of domestic, pet and wild birds. biconcave core or nucleoid containing the DNA. Adjacent to the
Natural poxvirus infections have been reported in about 232 core are two lateral bodies in each concavity (Fig. 13.3). All avian
species in 23 orders of birds (Bolte et al., 1999). While avian pox pox viruses have similar morphology.
virus infections are widely recognized, the information on the
host range as well as antigenic, genetic and biological diversity Transmission
of these viruses is not available. In the absence of such informa- In susceptible birds, avian pox virus infections occur through
tion, the classification has been based on the species that are mechanical transmission of the virus to the injured or lacerated
commonly infected or from which the virus was isolated. Con- skin. Small abrasions in the skin or mucous membranes allow
sequently, fowl, canary, junco, mynah, pigeon, psittacine, quail, the entry of the virus since it is unable to penetrate unbroken
starling, sparrow, turkey poxviruses are recognized within the tissue. Lacerations as a result of cannibalism, fighting or preening
genus Avipoxvirus of the family Poxviridae by the International may assist in the entry of the virus. Individuals handling birds at
Committee on Taxonomy of Viruses (https://talk.ictvonline. the time of vaccination may carry the virus on their hands and
org/ictv-reports). Fowlpox (FWPV) virus is the type species of clothing and may unknowingly deposit the virus in the eyes of