The pig intestine is considered as the natural reservoir for C. suis
, and the microbe seems generally to be well adapted to its host [1
]. In the present study, Chlamydia
spp. were demonstrated in high prevalence in all herds investigated. This is consistent with the few studies that have previously addressed the occurrence of Chlamydia
spp. in pig herds. Overall, it was not possible to relate the demonstration of the microbe to the presence of diarrhoea. However, based on the immunohistochemistry, pigs with diarrhoea might have been more heavily infected than the healthy pigs. This is in consistency with the results from another study on 447 pigs submitted for necropsy, where it was not possible to relate the presence of Chlamydia
spp. to the occurrence of diarrhoea, but in 12 cases, it was the only pathogen found [6
]. Similar experiences have also been noted in calves and sheep [24
In the study by Becker et al.
], C. suis
was significantly (P
< 0.0001) related to conjunctivitis in extensive pig production systems, whereas in intensive farming systems, high prevalences (88-90%) were found in both pigs with conjunctivitis and in clinically asymptomatic pigs. This is in accordance with the findings in the present study. Becker et al.
discussed, that environmental factors might predispose to infection. However, in one of the herds in the present study, factors such as emission of ammonium and carbon dioxide gases, air movements and overcrowding were investigated, but it was not possible to relate any environmental factor to the occurrence of conjunctivitis (data not shown). However, in one stable a high relative humidity (83%) was noted that might facilitate microbial survival. In the present study, the pigs originated from several piglet producing herds and it should be emphasized that intensive farming systems with the mixing of pigs from several sources also imply increased opportunities for microbial spread among animals of different immunological status. In fact, in one herd a significant relationship was noted between conjunctivitis and the presence of Chlamydia
spp. when the lower threshold value was applied in the real-time PCR. This might further indicate that the infectious load is important in the development of disease.
spp. was demonstrated in the ileal sections by immunohistochemistry in the present study, lesions compatible to those described in gnotobiotic pigs [9
] were only noted in 50% of the pigs. Several authors speculate that the development of lesions may depend on different factors such as the virulence of the strain, the infectious dose, the route of infection, or the age and the immunological status of the host [1
]. Since young, naive pigs seem to develop lesions in response to an experimental infection [9
], host immunity might be induced at an early age in the field [11
]. It is also possible that co-infections with other presumptive pathogens might act synergistically to exacerbate the lesions or that lesions induced by one microbe might increase the susceptibility to other infections. Several pathogens have been discussed in this respect [3
]. Most of the intestinal lesions described in the present study were shown to be related to infections with L. intracellularis
or B. pilosicoli
Some studies also report the occurrence of mixed infection with several chlamydial species [3
]. In wild boars, C. psittaci
was the dominating species but C. suis
and C. abortus
was also demonstrated by sequencing [31
]. In the present study, preliminary data obtained by PCR-RFLP indicated the co-infection by other species [34
]. However, sequencing of the amplicons revealed the involvement of C. suis
only, whereas other bands detected by PCR originated from E. coli
and un-identified bacterial species. The results underline the difficulties involved in the diagnosis and a large variation in reported prevalences between various detection methods exist [3
]. In the present study, the problem was circumvented by the use of an internal probe and a high melting temperature in the real-time PCR, combined with sequencing of the amplicons that assured a high specificity.