Feline Infektiöse Peritonitis - Histologische und immunhistologische Untersuchungen

Feline Infectious Peritonitis - Histological and immunohistological studies

In order to identify the biopsy site with the best diagnostic yield, this post-mortem study focussed on the spatial distribution of FIP characteristic changes throughout the feline organism. An immunohistochemical analysis furthermore was carried out to correlate tissue changes to the evidence intralesional coronavirus antigen.

The study enrolled 35 cats with confirmed FIP due to natural infection or experimental exposure upon vaccination. For histological and immunohistochemical testing, 53 locations were sampled from altogether 24 organs per cat.

In naturally infected cats, typical lesions were seen in 180 of 736 investi¬gated sites. Hundred-twentynine of 743 tested areas stained immuno¬histochemically positive for FeCoV. Both, the prevalence of FIP lesions (270/977) and the expression of FeCoV antigen (200/926) were insignificantly higher in vaccinated and challenged animals. The portion of pathognomonic foci in naturally infected cats varied from 8.5 - 47.7% and between 0 and 46.8% of sites per animal stained immunopositive. This corresponds to a frequency of 7.0 - 60.0% typical lesions and 5.7 - 48.0% positively tested sites in the experimentally infected group.

Typical FIP lesions most frequently were observed in the serosa of the liver, followed by liver parenchyma and mesenteric lymph nodes in group A. In experimentally infected cats, FIP lesions were most frequent in the serosa of the spleen, liver parenchyma, caecum and its serosal lining. The mesenteric lymph nodes came next.

Notably, FeCoV antigen was most prevalent in kidneys, lung, serosa of the liver, pancreatoduodenal and mesenteric lymph nodes and the eye, followed by visceral pleura, thymus, spleen and its serosa, ileum, colon and its serosa as well as the serosa of the duodenum. In group B, antigen was detected most often in the mesenteric lymph nodes and splenic serosa as well as in the pulp of the spleen and liver parenchyma, the caecum and its serosa and the visceral pleura.

Throughout both groups, lesions are more frequent than spots carrying FeCoV antigen. In spite of multifocal involvement, here is no single site that proves histologically positive in all FIP affected animals. These findings emphasis the need of multiple sampling sites in the living animal (liver, spleen plus mesenteric lymph nodes) to guarantee for a reliable evaluation concerning FIP due to FeCoV infection.