Characterization of Fowlpox virus in chickens and bird-biting mosquitoes: a molecular approach to investigating Avipoxvirus transmission.

Avian pox is a highly contagious avian disease, yet relatively little is known about the epidemiology and transmission of Avipoxviruses. Using a molecular approach, we report evidence for a potential link between birds and field-caught mosquitoes in the transmission of Fowlpox virus (FWPV) in Singapore. Comparison of fpv167 (P4b), fpv126 (VLTF-1), fpv175-176 (A11R-A12L) and fpv140 (H3L) gene sequences revealed close relatedness between FWPV strains obtained from cutaneous lesions of a chicken and four pools of Culex pseudovishnui, Culex spp. (vishnui group) and Coquellitidea crassipes caught in the vicinity of the study site. Chicken-derived viruses characterized during two separate infections two years later were also identical to those detected in the first event, suggesting repeated transmission of closely related FWPV strains in the locality. Since the study location is home to resident and migratory birds, we postulated that wild birds could be the source of FWPV and that bird-biting mosquitoes could act as bridging mechanical vectors. Therefore, we determined whether the FWPV-positive mosquito pools (n=4) were positive for avian DNA using a polymerase chain reaction-sequencing assay. Our findings confirmed the presence of avian host DNA in all mosquito pools, suggesting a role for Cx. pseudovishnui, Culex spp. (vishnui group) and Cq. crassipes mosquitoes in FWPV transmission. Our study exemplifies the utilization of molecular tools to understand transmission networks of pathogens affecting avian populations, which has important implications for the design of effective control measures to minimize disease burden and economic loss.

Identification of Clade E Avipoxvirus, Mozambique, 2016.

Analysis of scab samples collected from poultry during outbreaks of fowlpox in Mozambique in 2016 revealed the presence of clade E avipoxviruses. Infected poultry were from flocks that had been vaccinated against fowlpox virus. These findings require urgent reevaluation of the vaccine formula and control strategies in this country.

Characterization of canarypox-like viruses infecting endemic birds in the Galápagos Islands.

The presence of avian pox in endemic birds in the Galápagos Islands has led to concern that the health of these birds may be threatened by avipoxvirus introduction by domestic birds. We describe here a simple polymerase chain reaction-based method for identification and discrimination of avipoxvirus strains similar to the fowlpox or canarypox viruses. This method, in conjunction with DNA sequencing of two polymerase chain reaction-amplified loci totaling about 800 bp, was used to identify two avipoxvirus strains, Gal1 and Gal2, in pox lesions from yellow warblers (Dendroica petechia), finches (Geospiza spp.), and Galápagos mockingbirds (Nesomimus parvulus) from the inhabited islands of Santa Cruz and Isabela. Both strains were found in all three passerine taxa, and sequences from both strains were less than 5% different from each other and from canarypox virus. In contrast, chickens in Galápagos were infected with a virus that appears to be identical in sequence to the characterized fowlpox virus and about 30% different from the canarypox/Galápagos group viruses in the regions sequenced. These results indicate the presence of canarypox-like viruses in endemic passerine birds that are distinct from the fowlpox virus infecting chickens on Galápagos. Alignment of the sequence of a 5.9-kb region of the genome revealed that sequence identities among Gal1, Gal2, and canarypox viruses were clustered in discrete regions. This indicates that recombination between poxvirus strains in combination with mutation led to the canarypox-like viruses that are now prevalent in the Galápagos.

Fowlpox virus as a vector in non-avian species.

Examination of the members of the Poxvirus family reveals a large and diverse group with members infecting almost every animal species. To a large extent, members of the individual genera have a broad host range and infect a number of animal species, although, as Baxby has pointed out, successful experimental inoculation of a species does not necessarily mean that this species provides a natural host for that virus. Avipox viruses, together with swinepox virus occupy a somewhat unique position in possessing a restricted host range. We have taken advantage of this restricted host range in fowlpox virus to engineer recombinant vector viruses for use in the poultry industry and in vaccination of non-avian species.

Transmission studies involving a wet fowl pox isolate.

An isolate of fowl pox (FP) virus from a case of "wet" pox in commercial white leghorn (WL) pullets was used to expose WL cockerels via the comb-scratch (CS), eye-drop (ED), or laryngeal-swab (LS) route. Seven days postinoculation (PI), the groups challenged via CS had scabby proliferative pox lesions at the challenge site, the groups challenged via LS had slight dyspnea and rales, and 20% of the cockerels challenged via ED had mild conjunctivitis and lacrimation. By termination of the trial on day 21 PI, the CS-challenged groups had developed pronounced pox lesions. The LS-challenged groups showed severe dyspnea and rales with pronounced raised plaque-like lesions at the opening to the trachea and extending into the upper quarter of the trachea with heavy yellowish caseous exudate partly occluding the glottis. The ED-challenged groups had severe lacrimation and conjunctivitis and small pox lesions on the face, comb, and wattles; 12 of 18 had proliferative lesions on the oral mucosa in the area of the larynx. Forty-five percent of the LS-challenged groups died of suffocation. Pox virus was re-isolated from tissues in all treatment groups. Wet pox transmission appears to be possible via the LS and ED routes.

Psittacine pox virus: virus isolation and identification, transmission, and cross-challenge studies in parrots and chickens.

An avian pox virus was isolated from Amazon parrots dying with severe diphtheritic oral, esophageal, and crop lesions. The virus was propagated on chorioallantoic membranes (CAM) of 10-day-old chicken embryos, and a homogenate of the infected CAM was rubbed vigorously onto the conjunctiva, oral mucosa, and defeathered follicles of two healthy Amazon parrots and three conures. All experimental birds developed cutaneous and ocular pox lesions, and one parrot developed oral pox lesions. Specific-pathogen-free chicks inoculated with the virus isolate developed skin lesions identical to those of the parrots. Chickens vaccinated with fowl and pigeon pox vaccines and inoculated with the psittacine isolate developed lesions typical of avian pox. Chickens vaccinated with the psittacine virus were susceptible to fowl and pigeon pox virus infection. This pox virus isolate may thus be regarded as a potential pathogen for chickens.

Avian pox in birds from Trinidad.

Over a 7-year period in Trinidad, 9,514 birds were examined for avian pox and four species were found infected: the golden-headed manakin, Pipra erythrocephala (7% infected), the white-bearded manakin, Manacus manacus (5%), the violaceous euphonia Euphonia violacea (1%), and the bare-eyed thrush, Turdus nudigenis (less than 1%). The elaborate courtship displays of manakins may have a bearing on a "common source" type of infection. The apparently abrupt appearance of the disease at three localities in Trinidad in 1964 perhaps indicates introduction of the virus by migratory birds.

Avian pox infection in a Canada goose (Branta canadensis).

Lesions suggestive of Avian Pox were found on a debilitated Canada goose (Branta canadensis). These were demonstrated histologically to be characteristic poxvirus lesions and poxvirus particles were seen using electron microscopy. The virus was successfully transmitted to domestic geese but not to leghorn chickens or to domestic ducks.

Occurrence of atypical fowlpox in poultry farms in Kenya.

Atypical fowlpox occurred in several poultry farms in Kenya. On two occasions layers had their eyes closed and egg production dropped. Fowlpox virus was isolated from lesions on the inner surfaces of the closed eyelids. Other chickens had lesions covered by yellow caseous necrotic material in the mouth, around the epiglottis, and in the trachea and choanae. Typical proliferative cutaneous lesions were observed in birds of all ages in other flocks examined. Fowlpox virus was recovered from both cutaneous and diphtheritic lesions. The infected chorioallantoic membranes had focal hyperplastic lesions containing pink-staining intracytoplasmic inclusion bodies in most cells. Transmission studies showed that the virus was highly virulent to susceptible chickens.

Transmission of avian pox from starlings to Rothchild's mynahs.

Several wild species of birds, including starlings (Sturnus vulgaris), house sparrows (Passer domesticus) and pigeons (Columba livia) gained access to an aviary housing Rothchild's mynahs (Leucospar rothchildii) and over 100 additional birds representing a variety of species. Six of approximately 15 mynahs became infected with avian pox and all of them died. None of the other birds in the aviary developed lesions. Pox virus was isolated from mynah facial lesions on chicken chorioallantoic membrane and in duck embryo fibroblast cell culture. It did not produce lesions in white Leghorn chickens, but did produce lesions in 4 of 11 wild starlings captured outside the aviary. Results indicated the agent was an indigenous starling pox capable of infecting and producing disease in mynah birds. Destruction of the captive starlings and isolation of the remaining mynahs immediately stopped the mortality.