Occurrence of Avian Pox Outbreaks in Wild and Canary Commercial Breedings. Diagnosis through Electron Transmission Microscopy and Histopathology Techniques

Canary breeding is a practice that has become increasingly profitable and widespread in Brazil and plays a fundamental role in preservation of species. The yellow color of the Belgian lineage is the most popular, but the search for new and different tonalities, size, genetic improvement, besides presentation in exhibitions and preservation, are the main objectives of the creators [1].

Avian pox is one of the major viral diseases that affects canaries and due to its rapid spread, can decimate the entire breeding, causing great economic damages to breeders [2]. Canaripoxvirus species belongs to the Poxviridae family and Avipoxvirus genus [3]. Transmission involves insects as vectors, direct contact with aerosols between infected and susceptible birds, ingestion of water, contaminated food and semen transmission [2, 4, 5]. Three main forms characterize the disease, the cutaneous, diphtheric and septicemic, but coryza and tumor forms can also occur [6]. Cutaneous or dry is the most common in passerines, being characterized by the formation of nodules or vesicles in regions devoid of feathers, such as around the eyes, paws, feet and beak and in some cases, papules in the peri and infra-orbital regions, nose, sinus and tongue causing dyspnea and dysphagia [6]. In this form, the lesions can lead to blindness when they occur around the eyes and obstruct the passage of food or air when they occur around the mouth and esophagus. On the paws and feet, they make perching difficult, often leading to the development of secondary bacterial infections [7]. In the diphtheric or wet form, most commonly seen in parrots, fibronecrotic lesions (white plaques) occur on the membranes of the oral cavity, tongue, pharynx and larynx. Birds may have dyspnea and asphyxia due to laryngeal obstruction. Parrots and macaws can be affected by diphtheric enteritis with myocardial necrosis [6]. Canaries are the species most affected by the septicemic form, evidenced by the absence of skin lesions and the presence of pulmonary lesions [5]. There is also loss of appetite, ruffled feathers, cyanosis and solitude. The disease progresses to desquamative pneumonia with capillary occlusion resulting in dyspnea and death within 3 days, with mortality ranging from 70 to 90% [8]. A fourth form, coryza, affects parrots, which begins with clear nasal discharge that progresses to fibrinous and mucous membranes, followed by conjunctivitis. The form of tumors, represented by skin nodules that evolve into tumors and adenomas, is more commonly observed in canaries [6]. An unusual form of poxvirus was described in a herd of canaries, affecting mainly young animals, whose signs were respiratory distress, loss of feathers and crusts on the head, neck and back, anorexia, weight loss, ruffled feathers and high mortality [9]. Avipoxvirus was also isolated from tongue for canaries, that showed severe localized proliferative glossitis [10]and an outbreak of systemic avian pox associated with B1 subgroup was related among canaries [11]. Other outbreak of canaripox was reported inbreeder farms associated with co-infection by Mycoplasma gallisepticum [12]. In some birds, avipoxviruses may exist in a latent form [13,14] and may survive for months or even years in dry skin crusts [5]. More than one form can occur simultaneously in the same bird or indifferent birds from the same farm affected by the disease outbreak [6].

Secondary bacterial and fungal infections contribute to the worsening of the disease [15]. Nonspecific stressors may be associated with viral reactivation [6]. Birds with mild injuries can recover depending on their immunity, becoming carriers and spreading the virus [16].

In Brazil, there are few reports on the occurrence of the disease in wild birds, in captivity or commercial breeding. An outbreak of the disease occurred in 2003, was reported in an Ecological Park that affected several species, such as cowled-cardinal (Paroaria dominicana), white-throated seedeater (Sporophila caerulescens) and double-collared seedeater (Sporophila albogularis), with high mortality [17], and another outbreak that occurred in 2012 in the same Ecological Park, infected about 45 species of bay-winged-cowbird (Gnorimopsar chopi) [18]. Other occurrences signaled the presence of the virus in psittacines [19, 20], in a common barn owl (Tyto alba) [21], in penguins (Spheniscus magellanicus) [22] and in teal (Dendrocygna autumnalis) [23].

In commercial poultry, smallpox is a notifiable disease, being included in list B, among the communicable diseases considered important from a socio-economic and/or sanitary point of view at the national level and whose repercussions on the international trade of animals and products of animal origin are considerable [24].

This research aimed to detect the presence of avian poxvirus during outbreaks occurred in commercially farmed canaries and in an Ecological Parkin the State of São Paulo, SP, Brazil, using transmission electron microscopy and histopathology techniques.