Learn about Canine Coronavirus

ETIOLOGY

Canine Coronavirus (CCV) is a member of the Alphacoronavirus genus, belonging to the Coronaviridae family, which is part of the Nidovirales order (Figure 1). Different coronaviruses from this family infect a wide range of domestic species, including cattle, pigs, dogs, cats, horses, birds, rats, and mice. More recently, even humans have been affected. Several enteric strains of CCV have been isolated in outbreaks of diarrheal disease in dogs. It is known that this virus is antigenically related to Feline Coronavirus.

EPIDEMIOLOGIA

In 1971, a CCV was isolated from the feces of military dogs suspected of infectious enteritis. Since then, several outbreaks with isolations of similar Coronaviruses have occurred. CCV is highly contagious and spreads rapidly among susceptible groups of dogs. Serological studies indicate that infection is common, with seroprevalence reaching 100% in kennels and ranging from 6 to 75% in populations of pet dogs.

Fecal contamination of the environment is the primary source of transmission through ingestion. Infected dogs typically shed the virus for up to 9 days, and intermittent shedding may continue for months. The virus is not particularly resistant to the environment, and carrier dogs are necessary for its maintenance. In the absence of frequent reexposure to the virus, the duration of immunity may be relatively short. Genetic analysis results indicate that dogs can become infected with multiple strains simultaneously, as an infection with more than one preexisting genotype.

PATHOGENESIS

CCV can be shed in the feces of infected dogs between 3 and 14 days, up to 6 months after infection. After ingestion, CCV targets mature epithelial cells of the small intestine villi, where it is transported to the underlying lymphoid tissue. Uptake in the intestinal lymphoid tissue suggests that the virus may persist or remain latent in dogs, similarly to Feline Coronavirus.

The virus also replicates in epithelial cells and is released directly into the external environment. After the production of mature virus, infected cells develop severe cytoplasmic changes, and microvilli become shortened, distorted, and lost. The overall result is the accelerated loss of the villi from infected cells. The crypt epithelium is not destroyed; instead, hyperplasia develops. Unlike in Canine Parvovirus infection, villous necrosis and hemorrhage are rare.

Like other Coronaviruses, CCV can mutate, resulting in more virulent strains and corresponding increased severity of enteric disease. The highly virulent variant CB/05 has been found to cause fatal multisystemic disease, with clinical signs resembling those caused by Canine Parvovirus (CPV2), including hemorrhagic gastroenteritis and lymphopenia. Due to genetic mutation of enteric CCV, the pantropic Coronavirus has acquired its ability to spread internally to other tissues, similar to how Feline Infectious Peritonitis Virus arises from enteric FCoV.

CLINICAL SIGNS

Enteric Coronavirus infection is difficult to differentiate from other infectious causes of enteritis. The general consensus is that CCV infection is generally less severe than infection with Canine Parvovirus type 2. Clinical signs can vary widely, and the disease can affect dogs of any age, in contrast to CPV infections, where affected dogs are usually under 2 years old. Dogs with CCV infection often experience sudden onset of diarrhea, sometimes preceded by vomiting. Loss of appetite and lethargy are also common signs.

Signs can be more severe in infections with particularly virulent strains or in very young canine puppies. In severe cases, diarrhea may become watery and be followed by dehydration and electrolyte imbalances. Most affected dogs recover spontaneously after 8 to 10 days. When secondary complicating factors arise (parasites, bacteria, or other viruses), the disease can be prolonged significantly.

In pantropic Coronavirus infections, there are more severe symptoms, including fever (39.5 to 40°C), lethargy, anorexia, vomiting, hemorrhagic diarrhea, leukopenia, and neurological signs (ataxia, seizures) followed by death within 2 days. It would be difficult to distinguish these signs from those of Canine Parvovirus infection (CPV2). Dogs newly infected with enteric Coronavirus and subsequently challenged with the pantropic Coronavirus (CB/05 strain) showed milder clinical signs, leukopenia, and viral shedding, indicating only partial heterologous immune protection.

DIAGNOSIS

The virus can be detected in feces using immunochromatography, electron microscopy, or PCR. Serum neutralization or indirect immunofluorescence tests can be used to demonstrate an increase in antibody titers.

References

Veterinary Microbiology and Infectious Diseases / P. J. Quinn, B. K. … [et al.]; translated by Lúcia Helena Niederauer Weiss, Rita Denise Niederauer Weiss. Porto Alegre: Artmed, 2007.

Infectious Diseases in Dogs and Cats / Craig E. Greene; translated by Idilia Vanzellotti, Patricia Lydie Voeux. 4th ed. Rio de Janeiro: Guanabara Koogan, 2015.