Feline Infectious Peritonitis.

When I just googled this to find a picture- some pretty nasty looking ones came up! Not really something I want on the front page of my blog!

Organism

FIP is a mutation of feline coronavirus. Feline coronavirus alone generally causes an enteric disease. However, FIP has mutated so that it can multiply in macrophages. This leads to a widespread body granulomatous reaction. The disease is generally sporadic, although isolates of the disease from a singular household are more similar than within a geographical area which has a greater genetic variation.

Coronavirus:

• Enveloped +ve RNA Virus.
• Contains a nucleocapsid and glycoprotein spikes.
• In RNA viruses, RNA polymerase shows no proofreading. This leads to higher mutation rates at base pair level and recombination between coronaviruses as a component of the quasispecies theory. 
• Not all cats with coronavirus develop FIP. Infection with coronavirus is faecal-orally and generally affects cats in groups. Not all cats develop the disease as the virus strain, dose and the cat's immunity varies. 
• FIP is enhanced by antibodies and the main pathogenesis of FIP is by antibody-antigen complexes. This means that pre-existing antibodies to coronavirus increase the disease acceleration. This also means there is problems with developing a vaccine, as antibody responses would have an adverse effect on the disease.
• The Immune complexes act by depositing in the wall of small blood vessels leading to vasculitis. The antigen is already bound to the antibody and hence this enhances uptake by macrophages. Cats with NO antiviral antibodies therefore cannot develop FIP. 

Pathogenesis:

1. A shedding cat infects a susceptible cat ORONASALLY.
2. This leads to replication in the tonsils, URT and intestinal epithelia. 
3. This leads to multiplication in macrophages. 
4. Poor CMI-> wet variation of FIP. Partial CMI- Dry FIP. Good CMI-> recovery. If there is no multiplication in macrophages the cat sheds in the salivia and faeces. A recovered cat also sheds via these routes. 

Clinical Signs:

ALWAYS FATAL.

Wet FIP:

• Fluid in the body cavities.
• Fluctuating unresponsive fever. 
• Hepatomegaly, jaundice and abdomen swelling.
• Inappetence & weight loss.
• Muffling of heart sounds. 

Dry FIP:

• Anorexia, depression and lethargy.
• Signs dependent on the organs involved- CNS, eye or abdominal organs.
• Fluctuating fever.

Diagnosis:

• Definitive diagnosis-> histopath.
• FIP fluid- viscous and straw coloured, high protein content (globulins), froths when shaken and clots when standing.
• Blood chemistry-> neutrophilia, lymphopaenia, mild non regenerative anaemia, hyperproteinaemia (increased IG), albumin:globulin ratio decreases, and increases liver enzymes, bilirubin and urea. 
• Serology- 

1. Ab via ELISA.. +ve result does not mean the cat has FIP with certainty and shoudl be used in conjunction with other diagnosis.
2. Ag via PCR. Detects infection not disease. Needs single molecular deletion that predicts FIP for absolute diagnosis. 
3. Ab with IF-> results vary as different strains/techniques used. Goat anticat ab where cat ab adheres to cells infected with feline coronavirus. Experimental error so needs a four fold difference to be different. 

Treatment:

• Interferon.
• Always fatal. 

Transmission:

• Faeces.
• Salivia.
• Transplacental (1 in 3 queens). 

Epidemiology & Control:

• 75% breeding catteries and 25% pets positive for coronavirus. 
• Sporadic FIP- peak between 6 months to 2 years old.
• Asymptomatic carriers in seropositive healthy cats- faecal excretion for between 14 days to 7 months possibly cyclical. 
• In endemic breeding households kittens seroconvert by 10 weeks after loss of the MDA-> therefore isolate the queen 1-2 weeks prepartum, wean the kittens early with strict isolation, and check kittens still seronegative at ten weeks old. Appropriate hygiene should be ensured with an adequate number of litter trays, less cat and kitten numbers (max 8-10 adults) and keep groups stable to not introduce the disease.
• In rescue centres control encompasses batching cats, decreasing stress and thorough hygiene.