Detection of Paramyxovirus, Reovirus and Adenovirus Infection in King Snakes (Lampropeltis triangulum spp.) by Transmission Electron Microscopy and Histopathology Techniques.

The breeding of captive snakes in Brazil has become an important activity, whose main segments of the market are directed to the commercialization of venom, export of non-poisonous snakes, slaughter of animals for sale of meat and leather and supply of snakes for specialized pet shops in pets animal (Tutzer, 2006).

Lampropeltis triangulum (false coral snake, also called milk snake), is one of the most widely distributed snakes in the Americas, occurring from southern Ontario and Quebec in Canada, to Colombia, Ecuador and Venezuela in South America. Lampropeltis triangulum is a mostly crepuscular or nocturnal and terrestrial snake that kills by constriction. Its diet consisting of a variety of prey items including insects, worms, spiders, birds, small snakes, frogs and small mammals (Aguilar-Lopes & Pineda, 2013). Because they are docile, non-venomous and easily manipulated, king snakes are kept in captivity, as pets (kingsnake Brazil, 2009). The milk snake is not listed by the IUCN (International Union for Conservation of Nature), but in some areas, they may face significant pressure due to pet trade collection. Because of this species high value in the pet trade, many subspecies are now being bred in captivity for sale (Savitzky, 2004).

Reptilian paramyxoviruses belong to the Paramixoviridae family, genus Ferlavirus. They are negative sensed single stranded RNA viruses with a helical nucleocapsid packaged in a pleomorphic envelope (ICTV, 2016), and, among reptiles are found mainly in snakes of different families such as, Boidae, Elapidae, Colubridae, and Viperidae. Initially they were called ophidian paramyxovirus (OPMV) (Essbauer & Ahne, 2001), however, they were also isolated from lizards and tortoises (Marschang et al., 2009; Papp et al., 2010). 

The genus Ferlavirus refers to a reptilian isolate, which consists of Fer-de-Lance virus (FDLV) found in the common lancehead snake (Bothrops atrox) (Clark et al., 1979). 

Paramyxovirus is described as one of the major emerging agents that can threaten wildlife (Jacobson, 1993; Daszak et al., 2000) and is responsible for causing snake pneumonia (Marschang, 2011). 

Clinical signs associated with acute and chronic OPMV infection range from anorexia, occasional regurgitation, acute dyspnea, acute inspiration, pneumonia, emaciation, mucosal diarrhea, muscle weakness, head tremor, putrid odor and / or neurological disorders. The animals may also die without presenting any of the symptoms mentioned. Studies of OPMV isolated from snakes and other animals have shown that these are endogenous reptilian viruses (Ahne et al., 1987; Homer et al., 1995; Richter et al., 1996; Marschang et al., 2002; Sand et al., 2004; Jacobson and Samuelson, 2007; Abbas et al., 2011; Papp et al., 2013).

Recently a fatal systemic necrotizing infection associated with a novel paramyxovirus in Eunectes murinus juveniles was described (Woo et al., 2014).

Adenoviruses that infect reptiles are members of the family Adenoviridae, genus Atadenovirus. Virions are non-enveloped, 70–90 nm in diameter. The icosahedral capsid consists of 240 non-vertex capsomers (hexons), 8–10 nm in diameter, and 12 vertex capsomers (penton bases), each with a fiber protruding from the virion surface giving the characteristic morphology. The genome is a single, linear molecule of dsDNA and contains an inverted terminal repetition (ITR) (ICTV, 2016). Reptilian adenoviruses have already been documented in about 12 reptile species. Unlike mammalian and avian adenoviruses, reptilians were not well characterized in their pathogenic potential and the ability to induce a primary disease. Diagnosis by isolating the virus in fresh tissue is not always reliable and therefore confirmation of reptilian adenovirus infection depends on diagnosis by electron microscopy for the identification of virus particles associated with histopathological changes, such as the presence of nuclear inclusion corpuscles. Adenovirus infections were diagnosed in different species of snakes and associated with liver, gastrointestinal, respiratory and central nervous system disease (Heldstab & Bestett, 1984; Jacobson et al., 1985; Schumacher et al, 1994; Perkins et al, 2001; Kim et al., 2002; Raymond et al., 2003). 

Reptilian orthoreovirus belongs to the Reoviridae family, Spinareoviridae subfamily and Orthoreovirus genus (ICTV, 2016). Orthoreoviruses are non-enveloped viruses with an icosahedral capsid 70–80 nm in diameter (Attoui et al., 2011). The double-stranded RNA genome of orthoreoviruses consists of 10 segments grouped into three categories based on their electrophoretic mobility, three larges (L1-L3), three mediums (M1-M3), and four small segments (S1-S4 (ORF) (Day, 2009). They can induce cell-to-cell fusion. It has been demonstrated in several species of reptiles associated with sudden death, central nervous system disorders, skin lesions and pneumonia (Ahne et al., 1987; Marschang et al., 2002; Ducan et al., 2004, Ugurtas et al, 2008).

The knowledge of the viral infections that affect the king snakes, both kept in captivity as in free life, becomes important to elucidate many of the diseases that infect these animals, which may also constitute important zoonoses. Thus, this study aimed to report the simultaneous presence of paramyxoviruses, adenovirus and reovirus in snakes breeding, using transmission electron microscopy and histopathology techniques.