Epornitic of avian pox in common buzzards (Buteo buteo): virus isolation and molecular biological characterization

Molecular Detection of Avipoxvirus in Wild Birds in Central Italy

Simple Summary

Avipoxviruses (APVs) are responsible for diseases in domestic and wild birds. Currently, the disease in domestic animals is under control in many Countries by biosafety and vaccination. In wild birds, small disease events are frequently reported worldwide, but large outbreaks are generally rare. Nevertheless, some aspects of the epidemiology of these viruses are still unclear. In this study, we explored, through molecular investigations, the diffusion of APVs among wild birds, of different orders and species, without typical macroscopic lesions. A high percentage (43.33%) of positive specimens was detected, suggesting high diffusion of the viruses and a possible role of avian wildlife as a reservoir. Aquatic birds, mainly Anseriformes, were more often infected, probably in relation to the environment where they live; in fact, APVs are frequently transmitted by mosquitos, particularly abundant in humid areas.

Abstract

Avipoxviruses (APVs) are important pathogens of both domestic and wild birds. The associated disease is characterized by skin proliferative lesions in the cutaneous form or by lesions of the first digestive and respiratory tracts in the diphtheritic form. Previous studies investigated these infections in symptomatic wild birds worldwide, including Italy, but data about the circulation of APVs in healthy avian wildlife are not available. The present study tested spleen samples from 300 wild birds without typical lesions to detect Avipoxvirus DNA. Overall, 43.33% of the samples scored positive. Aquatic birds were more frequently infected (55.42%) than other animals (26.40%), and in Anseriformes, high positivity was found (52.87%). The obtained results suggest that wild birds could be asymptomatic carriers of Avipoxviruses, opening new possible epidemiological scenarios.

Multiple gene typing and phylogeny of avipoxvirus associated with cutaneous lesions in a stone curlew

Avipoxvirus (APV) infections have been observed in a wide variety of wild, captive and domestic avian hosts, recently including a range of island endemic and endangered species. However, not enough is known about genome diversity and phylogenetic relationships of APVs, as well as their host-range specificity. A wild stone curlew (Burhinus oedicnemus) was recovered in Sardinia (Italy), showing large wart-like lesions and nodules on both legs and toes, which resulted positive to poxvirus by PCR. Histopathological examination of the lesions showed ballooning degeneration and large intracytoplasmic inclusion bodies consistent with APV infection. A multiple gene sequencing approach was applied to highlight the phylogenetic relationships of this virus with a panel of selected APVs at the clade and subclade levels. This novel isolate was characterized by sequencing partial 4b core protein, P35 (locus fpv140) and DNA polymerase genes and phylogenetic analyses assigned it to clade A, (Fowlpox virus, FWPV), subclade A2. Conservation implications of avian pox presence in Sardinian stone curlews and possibly in other island bird species are discussed.

AVIAN POXVIRUS INFECTION IN A FLAMINGO (PHOENICOPTERUS RUBER) OF THE LISBON ZOO

Avian poxviruses (APV) are very large viruses spread worldwide in a variety of hosts. They are responsible for a disease usually referred to as pox, mainly characterized by nodular lesions on feather-free regions of the body. On May 2010, a young American flamingo (Phoenicopterus ruber) of the Lisbon Zoo (Portugal) developed a nodular lesion suggestive of poxvirus infection on its right foot. Avipoxvirus was isolated from the lesion and a fragment of the P4b-encoding gene was amplified by polymerase chain reaction. The nucleotide sequence of the amplicon was determined and analyzed. A close relationship (100% identity) was observed between the flamingo poxvirus and isolates from great bustard (Hungary 2005), house sparrow (Morocco 2009), MacQueen's bustard (Morocco 2011), and Houbara bustard (Morocco 2010 and 2011), suggesting interspecies transmission as a possible source of infection. To strengthen the investigation, the 5' and 3' ends of genes cnpv186 and cnpv 187, respectively, were also analyzed. The cnpv186-187 fragment exhibited 100% identity with MacQueen's bustard and Houbara bustard isolates, both from Morocco 2011. Phylogenetic analyses based in both fragments grouped the flamingo isolate consistently within clade B2 of canarypox. However, the phylogenetic relationships among the different representatives of avian poxviruses were more comprehensive in the tree based on the concatenated coding sequences of the cnpv186-187 fragment, rather than on the P4b-coding gene. The clearer displacement and distribution of the isolates regarding their host species in this last tree suggests the potential usefulness of this genomic region to refine avian poxvirus classification.

Diversity of avipoxviruses in captive-bred Houbara bustard

Implementation of conservation breeding programs is a key step to ensuring the sustainability of many endangered species. Infectious diseases can be serious threats for the success of such initiatives especially since knowledge on pathogens affecting those species is usually scarce. Houbara bustard species (Chlamydotis undulata and Chlamydotis macqueenii), whose populations have declined over the last decades, have been captive-bred for conservation purposes for more than 15 years. Avipoxviruses are of the highest concern for these species in captivity. Pox lesions were collected from breeding projects in North Africa, the Middle East and Central Asia for 6 years in order to study the diversity of avipoxviruses responsible for clinical infections in Houbara bustard. Molecular and phylogenetic analyses of 113 and 75 DNA sequences for P4b and fpv140 loci respectively, revealed an unexpected wide diversity of viruses affecting Houbara bustard even at a project scale: 17 genotypes equally distributed between fowlpox virus-like and canarypox virus-like have been identified in the present study. This suggests multiple and repeated introductions of virus and questions host specificity and control strategy of avipoxviruses. We also show that the observed high virus burden and co-evolution of diverse avipoxvirus strains at endemic levels may be responsible for the emergence of novel recombinant strains.

Two different avipoxviruses associated with pox disease in Magellanic penguins (Spheniscus magellanicus) along the Brazilian coast

A novel avipoxvirus caused diphtheritic lesions in the oesophagus of five and in the bronchioli of four Magellanic penguins (Spheniscus magellanicus) and also cutaneous lesions in eight Magellanic penguins housed in outdoor enclosures in a Rehabilitation Centre at Florianópolis, Santa Catarina State, Brazil. At the same time, another avipoxvirus strain caused cutaneous lesions in three Magellanic penguins at a geographically distinct Rehabilitation Centre localized at Vila Velha, Espírito Santo State, Brazil. Diagnosis was based on clinical signs, histopathology and use of the polymerase chain reaction (PCR). Clinical signs in the penguins included cutaneous papules and nodules around eyelids and beaks, depression and restriction in weight gain. The most common gross lesions were severely congested and haemorrhagic lungs, splenomegaly and cardiomegaly. Histological examination revealed Bollinger inclusion bodies in cutaneous lesions, mild to severe bronchopneumonia, moderate periportal lymphocytic hepatitis, splenic lymphopenia and lymphocytolysis. Other frequent findings included necrotizing splenitis, enteritis, oesophagitis, dermatitis and airsacculitis. Cytoplasmic inclusion bodies were seen within oesophageal epithelial cells in five birds and in epithelial cells of the bronchioli in four penguins. DNA from all samples was amplified from skin tissue by PCR using P4b-targeting primers already described in the literature for avipoxvirus. The sequences showed two different virus strains belonging to the genus Avipoxvirus of the Chordopoxvirinae subfamily, one being divergent from the penguinpox and avipoxviruses already described in Magellanic penguins in Patagonia, but segregating within a clade of canarypox-like viruses implicated in diphtheritic and respiratory disease.

Phylogenetic and histological variation in avipoxviruses isolated in South Africa

Thirteen novel avipoxviruses were isolated from birds from different regions of South Africa. These viruses could be divided into six groups, according to gross pathology and pock appearance on chick chorioallantoic membranes (CAMs). Histopathology revealed distinct differences in epidermal and mesodermal cell proliferation, as well as immune cell infiltration, caused by the different avipoxviruses, even within groups of viruses causing similar CAM gross pathology. In order to determine the genetic relationships among the viruses, several conserved poxvirus genetic regions, corresponding to vaccinia virus (VACV) A3L (fpv167 locus, VACV P4b), G8R (fpv126 locus, VLTF-1), H3L (fpv140 locus, VACV H3L) and A11R–A12L (fpv175–176 locus) were analysed phylogenetically. The South African avipoxvirus isolates in this study all grouped in clade A, in either subclade A2 or A3 of the genus Avipoxvirus and differ from the commercial fowlpox vaccines (subclade A1) in use in the South African poultry industry. Analysis of different loci resulted in different branching patterns. There was no correlation between gross morphology, histopathology, pock morphology and phylogenetic grouping. There was also no correlation between geographical distribution and virus phenotype or genotype.

Emerging and reemerging diseases of avian wildlife

Of the many important avian wildlife diseases, aspergillosis, West Nile virus, avipoxvirus, Wellfleet Bay virus, avian influenza, and inclusion body disease of cranes are covered in this article. Wellfleet Bay virus, first identified in 2010, is considered an emerging disease. Avian influenza and West Nile virus have recently been in the public eye because of their zoonotic potential and links to wildlife. Several diseases labeled as reemerging are included because of recent outbreaks or, more importantly, recent research in areas such as genomics, which shed light on the mechanisms whereby these adaptable, persistent pathogens continue to spread and thrive.

Avian pox infection in a free-living crested serpent eagle (Spilornis cheela) in southern Taiwan

Avian pox viruses (APVs) have been reported to cause infection in diverse avian species worldwide. Herein we report the first case of APV infection in a free-living bird, a subadult crested serpent eagle (Spilornis cheela), in Taiwan. In addition to the typical wart-like lesions distributed on the cere, eyelid, and face, there were also yellowish nodules below the tongue and on the hard palate. Phylogenetic analysis of the 4b core protein gene showed that the APV is very close to that found in white-tailed sea eagle (Haliaeetus albicilla) in Japan recently. Because both cases are located on the same major flyway for migratory birds, the impact of this virus with regard to the wild and migratory raptor species along the East Asian-Australasian Flyway and West Pacific Flyway requires immediate investigation.

Avipoxviruses: infection biology and their use as vaccine vectors

Avipoxviruses (APVs) belong to the Chordopoxvirinae subfamily of the Poxviridae family. APVs are distributed worldwide and cause disease in domestic, pet and wild birds of many species. APVs are transmitted by aerosols and biting insects, particularly mosquitoes and arthropods and are usually named after the bird species from which they were originally isolated. The virus species Fowlpox virus (FWPV) causes disease in poultry and associated mortality is usually low, but in flocks under stress (other diseases, high production) mortality can reach up to 50%. APVs are also major players in viral vaccine vector development for diseases in human and veterinary medicine. Abortive infection in mammalian cells (no production of progeny viruses) and their ability to accommodate multiple gene inserts are some of the characteristics that make APVs promising vaccine vectors. Although abortive infection in mammalian cells conceivably represents a major vaccine bio-safety advantage, molecular mechanisms restricting APVs to certain hosts are not yet fully understood. This review summarizes the current knowledge relating to APVs, including classification, morphogenesis, host-virus interactions, diagnostics and disease, and also highlights the use of APVs as recombinant vaccine vectors.