Occurrence of the Distemper Canine: Ultrastructural and Histophatological Aspects

Canine distemper is a highly contagious disease that mainly affects dogs of all ages. The disease is caused by a paramyxovirus belonging to the Paramyxoviridae family of the genus Morbilivirus. This genus includes, in addition to canine distemper virus (CDV), rinderspest virus (RPV), peste des petits ruminants virus (PPRV) and measles virus (MV) (Grifin, 2007). Paramyxoviruses (PMVs) are enveloped particles, with nucleocapside helicoidal and negative-sense, single-stranded RNA viruses with genes coding for at least six major proteins, nucleocapsid (N), phosphoprotein (P), matrix (M), fusion glycoprotein (F), receptor binding protein (RBP, formerly designated variously as HN, H, or G),and the large protein (L) that possesses RNA-dependent RNA polymerase (RdRp) activity (Rima et al., 2019). CDV has a tendency to cross the species barrier by infecting species other than Canidae, such as Mustelidea, Procyonidae, Ursidae and Viverridae (Greene et al., 2012). Phylogenetic studies suggest that paramyxoviruses related to human mumps virus (MuV, Rubulavirus) and canine distemper virus (CDV, Morbillivirus) in host bats may have the potential to create spillover events and cause disease in other mammalian species (Drexler et al., 2012).

The disease has a high socioeconomic impact in the Brazilian veterinary field due to the high cost of treatment, failures in vaccine immunization and the suffering of animals and guardians (Headley et al., 2012). In the wild, it is considered an emerging disease, since wild canids are vulnerable (Jucá et al., 2022), such as lions, tigers, leopards (Appel et al., 1994) and monkeys (Sun et al., 2010). The disease has also been described in aquatic mammals and cetaceans such as dolphins (Stone et al., 2011). In the United States, the occurrence of contamination from domestic dogs to raccoons indicates that they can act as intermediate hosts (Kapil et al., 2008). In other countries such as Italy, distemper represents an immediate problem due to the illegal trade in puppies from east Europe (Dall'ara, 2020; Mira et al., 2018).

The disease presents in 2 forms, overacute, characterized by fever and sudden death, and acute, when the animals show signs of fever, prostration, lack of appetite, nasal and ocular secretions, conjunctivitis, vomiting, respiratory distress, anorexia, diarrhea, dehydration, and cutaneous rash, in addition to neurological symptoms such as paralysis, seizures and death (Oliveira et al., 2008).

Histologically, canine distemper virus produces necrosis of lymphatic tissues, interstitial pneumonia, and cytoplasmic and intranuclear inclusion bodies in respiratory, urinary, and gastrointestinal epithelium, neuronal degeneration, encephalitis, meningitis and intranuclear inclusion bodies (Origgi et al., 2012). The duration and severity of the disease depend on factors such as the animal immune status, strain virulence, affected organs, among others. The course can be short (10 days) or go on for weeks or months. The mortality rate ranges from 30 to 80% and surviving animals may recover normally or have permanent central nervous system sequelae or late complications such as demyelinating encephalitis (old dog encephalitis), ascending paresis, paralysis, convulsions and hyperkeratosis of the paws, which can lead to the death of animals. Young dogs are more susceptible, but everyone regardless of age can be affected. Dogs that recover from acute disease with persistent infection may shed virus in urine and through the skin on the foot pads. Transmission occurs through aerosols or contaminated food and objects (Beineke et al., 2009; Martella et al., 2008; Kapil & Yeary, 2011).

This work aimed to investigate the presence of paramyxovirus in samples of feces, urine, ocular and nasal swabs and organ fragment from dogs, using transmission electron microscopy and histopathology techniques.