Seroepidemiological survey for Chlamydophila felis among household and feral cats in northern Italy

Chlamydophila felis is thought to be an important ocular pathogen in cats. Conjunctivitis caused by C felis has been reported in many countries by several authors (Moraillon 1988, Wills and others 1988, Hanselaer and others 1989, Pointon and others 1991, Gruffydd-Jones and others 1995, Pudjiatmoko and others 1996, McDonald and others 1998, Sykes and others 1999, Cai and others 2002). In Italy, previous serological investigations using the complement fixation test and ELISA showed seroprevalence rates for chlamydiosis ranging from 2 to 13 per cent in populations of free-living feral cats (Piccoli and Capelli 1991, D’Amore and others 1997) and from 10 to 15 per cent in household cats (Ferrari and others 1992). These seroprevalences were lower than those found in other countries during surveys of feral and household cats using the homologous indirect immunofluorescence antibody (IFA) test (Wills and others 1988, Pudjiatmoko and others 1996, Yan and others 2000). This difference may be ascribable to a number of factors, such as limited circulation of the pathogen in the Italian feline population, the different types and sizes of populations examined, and the types of serological test used. This short communication describes a study to test this last hypothesis by determining the prevalence of antibodies to C felis in sera from cats registered at a serum collection bank by a homologous IFA test. A total of 430 serum samples, collected between October 1997 and November 2000 in the Veneto region of northern Italy, were examined; there were 254 samples from household cats and 176 from feral cats, which belonged to two catteries and 15 colonies of free-living cats. The free-living feral cats were blood sampled during a programme of neutering carried out by veterinarians of the public veterinary service. The IFA test was performed using as antigen the purified elementary bodies of a chlamydial isolate from a conjunctival swab taken from a cat kept in a cattery in Bologna, in the Emilia-Romagna region of northern Italy (Di Francesco and others 2004). The elementary bodies were purified by sucrose density-gradient ultracentrifugation by the method described by Fukushi and Hirai (1988). The presence of C felis antibodies was assessed using a fluorescein-conjugated goat anticat immunoglobulin G serum (Euroclone). The IFA test was carried out according to the method of Wills and others (1988). Sera were screened at 1:16 and 1:32 dilutions. Sera that fluoresced an apple-green colour at 1:32 dilution were considered to be positive, and were tested by serial dilution to determine the antibody titre. The reciprocal of the highest serum dilution showing apparent fluorescence was considered to be the antibody titre of that sample. The results of the IFA test for C felis antibodies are shown in Table 1. Overall, 130 (30·2 per cent) of the 430 samples tested positive, 54 (21·3 per cent) of the 254 household cats, 58 (64·0 per cent) of the 90 cattery cats and 18 (21·0 per cent) of the 86 free-living feral cats testing positive. The seroprevalence rates in the two catteries were 68·0 per cent and 36·0 per cent. Seropositive animals were found in six of the 15 feral populations investigated. Antibody titres ranged from 32 to 2048 in the household and cattery cats, and from 128 to 2048 in the free-living cats. When the seroprevalences were compared by the chisquared test, the seroprevalence was significantly higher in the cats kept at the two catteries than in the free-living feral cats (χ2=33·94; P=0·001) and the household cats (χ2=56·44; P=0·001). Additionally, the seroprevalences in the free-living and household cats were virtually identical. This may be due to the epidemiological features of C felis, the transmission of which requires close contact between infected and healthy animals. This appears to be more frequent within closed feline communities, such as residential and boarding catteries and breeding centres, where unavoidable contact among animals, within a restricted space, favours the spread of infection. Among the 15 free-living feral populations tested, the infection appeared to be endemic in six colonies and absent in nine. The lower distribution of C felis might be due to the fact that these are free feline communities in which the cats are not forced to have contact with one another. With regard to the household cats which tested positive for antibodies to C felis, they had come from catteries or pet shops and lived in a semi-free condition, implying that they were able to have contact with other cats. In all the categories of cats tested, it was not possible to assess whether there was any correlation between the cats’ antibody status and the presence of clinical signs suggestive of chlamydiosis, because the collection of data had been focused on other pathologies. A few of the cats had antibody titres at or above 1024, comparable with those found in other investigations of cats with active chlamydial infection (Wills and others 1988). Lower antibody titres may only be suggestive of a contact with C felis, but may not be indicative of when infection occurred, because cats experimentally infected with chlamydiae showed high antibody titres which persisted for more than a year after the onset of the infection (Wills 1986). In conclusion, the results of the IFA test showed that there was a high seroprevalence for chlamydiosis in cats in the area surveyed, especially in closed feline populations, and confirmed that the homologous IFA test is a reliable tool for the serological diagnosis of feline chlamydiosis. Veterinary Record (2004) 155, 399-400