The natural source of FIPV was represented by a group of 10 clinically healthy cats from animal shelters which were tested positive for circulating FCoV immune complexes by means of a competitive ELISA.

During the experiment, most of the 40 SPF cats developed FIP. One SPF cat survived a presumed FIPV infection with clinical manifestation and remained clinically healthy after the symptoms had resolved. Necropsy at the end of the experiment did not reveal any FIP-specific lesions.

During the experiment, seven SPF cats (17.5%) did not show any clinical symptoms. None of these animals who all were necropsied at the end of the experiment, exhibited FIP.

The clinical status of most cats originating from animal shelters, remained unaltered throughout the experiment. One of these cats, however, developed and died of coronavirus enteritis.

Twenty-three cats (45%) died of or were euthanatized in the final stage of FIP during the experiment.Ten of these animals were control SPF cats, 12 animals were Primucell ® FIP vaccinated SPF cats, and one animal was originating from an animal shelter.

Concerning the number of cats developing FIP, there was neither a significant difference between Primcell ® -vaccinated and control SPF cats (p=0.53) nor with regards to the sex distribution. The experiment yielded a protected/preventable fraction of –20%, that is to say, no protection by Primcell ® FIP vaccination occurred.

Pathologically, FIP was mainly represented by the effusive form (65%) which mostly appeared in the classical form. The clinical course was often fulminant with short duration of disease. In general, ascites represented the first symptom and showed fast progression.

With the dry form of FIP which occurred throughout the whole experiment, symptoms were mainly non-specific. In one animal, clinical signs were restricted to CNS symptoms.

Neither duration nor the course of disease were affected by symptomatic therapy. At the same time as the clinical signs of FIP or prior to their development, more than 80% of the animals had clinical signs of upper respiratory disease, where as only 44 % of the FIP-negative cats developed such symptoms.

During the experiment, all SPF cats showed seroconversion. The vaccine Primucell ® FIP induced CoV anitbody titres of 1:50 up to 1:800. With the onset of infectious pressure, CoV antibody titres rised to >3200 in some animals. Animals who developed high CoV antibodytitres or showed a positive result in the competitive ELISA for circulating FCoV immune complexes did not necessarily develop FIP.

Regardless of the presence of clinical symptoms, cats with a positive result in the competitive ELISA for circulating FCoV immune complexes in sera or exudates have to be regarded as potential source of FCoV infection for susceptible animals. CoV antibody titres do not allow a prognosis concerning the development of FIP.

At the end of the experiment, monocyte-associated FCoV viraemia was identified by RT-PCR in nearly all animals who had survived (20 of 23).