Seroprevalence to chlamydiae in pigs in Italy

ACCORDING to the current taxonomy (Everett and others 1999), four chlamydial species, namely Chlamydia suis (formerly the porcine serovar of Chlamydia trachomatis), Chlamydophila psittaci (formerly avian serovars of Chlamydia psittaci), Chlamydophila abortus (formerly ovine serovars of C psittaci) and Chlamydophila pecorum (formerly Chlamydia pecorum) have been isolated from pigs. Chlamydiae in pigs can cause asymptomatic infections and have been associated with pneumonia, polyarthritis, pericarditis, conjunctivitis, enteritis, reproductive disorders and increased perinatal mortality (Martinov and others 1985, Woolen and others 1990, Rogers and others 1993, Andersen 1994, Zahn and others 1995, Thoma and others 1997, Guscetti and others 2000, Becker and others 2004, Sachse and others 2004). It is widely believed that chlamydiae may act together with other agents in multifactorial infectious diseases (Pospischil 2004). Chlamydial infections in pigs have been reported mainly in eastern European countries, Austria, Germany, Switzerland and Belgium. In Italy, chlamydiae were detected in fetal organs by direct immunofluorescence, and seropositivity was shown by the complement fixation test in 26 of 100 sows with reproductive problems (Sala 2003). This short communication describes a study to determine the seroprevalence of C suis, C pecorum, C abortus and C psittaci by the microimmunofluorescence test (MIF) in 337 pigs from 11 intensive farms located in northern Italy. Serum samples were collected randomly from finishing pigs at an abattoir in 2004. The MIF was performed using purified elementary bodies (EBs) of the four different species as antigens: the Italian C suis isolate MS04, obtained from a conjunctival swab from a pig; the Italian C pecorum isolate PV5268, obtained from a bovine cervical swab; the ovine reference strain S26/3 of C abortus; and the avian reference strain 6BC of C psittaci. MS04 and PV5268 had been characterised by molecular analysis. The EBs were purified by sucrose density-gradient ultracentrifugation by the method of Fukushi and Hirai (1988). The presence of chlamydial antibodies was assessed using fluorescein-conjugated goat anti-pig immuno globulin G serum (Euroclone). The sera were screened at 1:32 dilution in phosphate-buffered saline supplemented with 2 per cent fetal calf serum. The test was performed according to the method of Wang and Grayston (1986). Serial twofold dilutions of the sera that tested positive at 1:32 dilution were tested to determine the antibody titre. The reciprocal of the highest serum dilution showing an apple-green fluorescence of EBs was considered to be the antibody titre. Antibodies to C suis were detected in 214 of the 337 (63·5 per cent) samples tested, with antibody titres ranging from 32 to 512. Seropositivity to C suis was observed in pigs from all 11 farms investigated, ranging from 20 per cent to 100 per cent (mean 61 per cent). Only a few sera with high antibody titres to C suis reacted weakly at 1:32 dilution with the other chlamydial species. No antibody titres above 32 were detected in any sera to C pecorum, C abortus or C psittaci. The high chlamydial seroprevalence is consistent with the results of serological surveys performed in other countries. Wendt and others (1998) reported a chlamydial seropositivity ranging from 4 per cent to 72 per cent in breeding sows in Germany, in a study that used an ELISA for antibodies to the chlamydial-specific lipopolysaccharide (LPS) antigen; significantly higher percentages of seropositive sows were found in herds with reproductive disorders. Vanrompay and others (2004) reported seropositivity in 96·5 per cent of 258 closed pig breeding farms in Belgium, tested by an indirect ELISA using C psittaci recombinant major outer membrane protein as antigen. Camenisch and others (2004) reported that 61·7 per cent of 193 sera taken from Swiss herds of sows with or without reproductive problems were positive for antibodies to LPS of Chlamydiaceae, with no significant difference between the two groups of herds. In those studies, family-specific antibodies were detected. In the present study, the MIF performed with EBs of the different chlamydial species allowed the evaluation of species-specific seroreactivity and showed a high seroprevalence for C suis. Since antichlamydial vaccines are not administered in pig herds, this seropositivity suggests that the pigs had extensive contact with C suis. The association of C suis with the porcine intestinal tract (Schiller and others 1997a, Hoelzle and others 2000) and its shedding in faeces could increase its spread on farms. C suis is associated with conjunctivitis, enteritis and pneumonia (Rogers and Andersen 2000, Merialdi and others 2003, Sachse and others 2004); it has also been detected in fetal organs from porcine abortions together with C pecorum (Schiller and others 1997b), and in cervical swabs of sows with reproductive problems in association with C abortus (Hoelzle and others 2000). In the present study, the history of the herds described respiratory and reproductive problems on only two farms and on these farms seroprevalences of 75 per cent and 66 per cent against chlamydiae were detected. Since these farms did not test for antibodies to other infectious agents, the association between the C suis seropositivity and the clinical signs is not clear. The remaining nine farms, which showed seropositivity ranging from 20 per cent to 100 per cent (mean 59 per cent), did not report clinical signs suggestive of chlamydiosis. The seropositivity on these farms could be due to asymptomatic infections; for example, intestinal chlamydiosis seems to be a mainly subclinical condition (Nietfeld and others 1997). Further investigations are needed to assess the role of C suis as a bacterial pathogen in pigs.