Coronaviruses see also ⇒ SARS-CoV-2
Coronaviruses are enveloped RNA viruses which have club-shaped appendages on their surface that look like a crown under the electron microscope and have thus given the virus family its name. As they are genetically highly variable, transmission of corona viruses to and among different species is possible. They belong to a large group of RNA viruses that can cause respiratory and/or enteral diseases in various animal species and in humans.
An infection with canine (enteric) coronaviruses (CCoV, CCV, more recently also CECoV) is usually asymptomatic or may lead to mild, non-haemorrhagic diarrhoea. In puppies, however, severe courses of the disease with haemorrhagic gastroenteritis are possible. Loss of intestinal villi, flattening of the epithelial cells of the small intestine and detachment of the goblet cells occur. The most noticeable signs are vomiting and watery to bloody diarrhoea, accompanied by severe dehydration. The virus is excreted via the faeces; the duration of excretion is usually less than two weeks.
CCV is also infectious to other canids as well as to cats and pigs, but the pathogenicity of these species is not yet known.
Canine respiratory coronavirus (CRCoV) was first detected in a dog in 2003. It appears to have originated from bovine coronavirus, since both viruses share very close similarities. In general, respiratory coronavirus can frequently be detected in the majority of dogs suffering from kennel cough (also known as canine infectious respiratory diseases (CIRD) complex).
In many dogs with mild or moderate signs, such as cough or nasal discharge, but also
in asymptomatic dogs, the virus can mainly be found in the trachea.
Feline coronaviruses (FCoV) can be divided into two pathotypes: the weak to non-virulent feline enteric coronavirus (FECV), which infects the intestinal epithelial cells and is considered a mere “diarrhoea pathogen”, and the usually fatal feline infectious peritonitis virus (FIPV), which mutates in cats and can replicate massively in macrophages.
A cat from a multi-cat household is more likely to excrete the virus than a cat from a single-cat household. The higher the infection pressure, the more likely it is that enteric coronaviruses mutate and cause FIP.
If FIP develops, two different clinical manifestations can be observed: the wet exudative form and the dry granulomatous form. In the wet form, severe polyserositis develops with the formation of a highly viscous, yellowish, fibrin-containing ascites fluid. In the dry form of FIP, pyogranulomatous swellings form on the serosa and in the organs. This mainly affects the liver, lungs and kidneys. Inflammatory nodules form on the spleen and the lymph nodes. Cats often develop anaemia with icterus, emaciation and high fever. There may also be CNS symptoms and, due to the deposition of precipitates, uveitis.
A positive titre indicates that the cat had been in contact with coronaviruses. This is the case with most adult animals. In a clinically healthy animal, high titres are usually not important. They do not suggest that this cat will contract FIP. FEVC excretors can be identified by means of PCR. In animals suffering from FIP, there are often only low to negative antibody titres. In this case, the antibodies have been bound in immune complexes; thus, antibodies are no longer detectable. For further evaluation, a serum protein electrophoresis and the determination of the albumin-globulin ratio can be included. Diagnostic information is provided by an increase in the gamma globulin fraction and an albumin-globulin ratio below 0.6. The albumin-globulin ratio is 92% specific.
Ferret enteric coronavirus can cause epizootic catarrhal enteritis (ECE) in ferrets with mucoid, greenish, malodorous diarrhoea, especially in adult animals. It is shed in saliva and faeces.
Ferret systemic coronavirus can cause a disease similar to FIP, which mainly affects ferrets under 18 months of age. Signs may be non-specific (including diarrhoea, weight loss, lethargy, hyporexia/anorexia, vomiting). In some cases, neurological signs, such as paresis, ataxia, tremor or seizures, can be observed.
Equine coronavirus (ECoV), a beta coronavirus, was first detected in the USA in 1999 in the faeces of a foal suffering from diarrhoea. Recent studies in the USA, Japan and Europe confirm it is associated with fever, colic and diarrhoea particularly in adult horses. Infections caused by ECoV mostly occur in the cold season (November to May); involvement of the respiratory system has not yet been proven.
Clinical signs include anorexia, lethargy, fever and changes in faecal consistency. Diarrhoea and mild colic symptoms may also occur. Neurological abnormalities (ataxia, depression, recumbency) have rarely been described, they were, however, secondarily caused by hyperammonaemia. The blood count shows leukopenia (neutropenia/ lymphopenia) and hypoalbuminaemia.
Infections with ECoV seem to be self-limiting but can be secondarily complicated (e. g. dehydration or intestinal displacement). Transmission is mainly via the faecal-oral route.
Bovine coronaviruses (BCoV) cause enteric and respiratory diseases in cattle and wild ruminants. These include calf diarrhoea, winter dysentery in adult cattle and respiratory diseases in cattle of different ages.
In pigs, coronaviruses cause highly contagious, sometimes epidemic transmissible gastroenteritis (TGE). TGE virus presents an economic problem in all countries with intensive pig production. Loss of income occurs in the affected farms as a result of piglet losses, growth retention and reduced weight gain.
An infection with porcine coronavirus leads to a local infection of the intestinal tract, mostly in the jejunum and ileum. As the disease progresses, the villous epithelium is rapidly lost. Clinically, this is manifested in a watery malodorous diarrhoea. In Germany, TGE is a notifiable animal disease.