Seroepidemiological investigation on Chlamydophila felis in humans in northern Italy

Chlamydophila felis is a significant cause of conjunctivitis in cats in many countries. The transmission of chlamydial conjunctivitis from cats to human is possible, but a close contact is needed, so the risk for cat owners and people working in contact with cats is high. There have been very few reports in this connection, possibly because the transmission from cats to humans is a rare occurrence, or because such cases are underestimated as a result of failed isolation or inadequate investigation. In view of the C. felis circulation observed among feline populations, a seroepidemiological study was carried out about the circulation of C. felis in humans with and without contact with cats, using a microimmunofluorescence test (MIF). To verify cross-reactions with other species of chlamydiae, all the positive sera were tested by MIF also against C. psittaci and C. pneumoniae, and by immunoblotting analysis, to evaluate their reactivity to proteins of the three chlamydial species. A strong cross-reactivity between C. felis and C. pneumoniae was observed by MIF. By immunoblotting, all the C. felis-positive sera showed a strong reactivity with C. pneumoniae antigens, but a weak reactivity to C. felis and C. psittaci proteins. The results suggest no specific reactivity to C. felis in the sera examined. It is possible that, in the past, several cases of human diseases ascribed to C. felis infection on the basis of a not species-specific serology, were really due to C. pneumoniae. So, in the course of seroepidemiological surveys on feline chlamydiosis in the human population, cross-reactions between C. felis and C. pneumoniae should always be evaluated because of the higher seroprevalence of C. pneumoniae in the adult human population.