Epidemiological surveillance of PRRS in pig farms from Yucatán, Mexico.

The acquisition of replacement gilts represents the main risk for the introduction of the disease to negative farms, or in this case, for the introduction of new virus variants to positive farms. The possibility of boars transmitting PRRS is important even when the animal does not show signs of the disease after infection.

To determine the health status of replacement gilts and boars used for natural mating or semen donors regarding the virus of PRRS in farms using different control/prevention measures for the disease.

Blood samples were obtained in order to extract serum from animals of 23 farms that produce their own gilt replacements, four samplings were carried out. Other 25 farms which use natural mating were also sampled. Sera were tested with the ELISA-herdChek® X3 PRRS, in order to determine the status of the animals regarding the disease. ELISA positive samples were tested with a Polymerase chain reaction procedure specific for PRRS virus, trying to find evidence of the actual virus. It is important to stress that in Yucatan there aren´t registers of PRRS samplings as in other parts of Mexico.

Eight out of 25 (32%) farms with boars resulted positive to PRRS virus by serology. 36 sera out of 128 (28.13%) from boars, were positive in the ELISA X3. Fifteen out of 23 (65.22%) farms using self-replacement gilts were positive to PRRS virus while 625 sera out of 1414 (44.21%) obtained from replacements gilts were positive to the ELISA X3. Four quarantine areas with 155 animals were tested with no positive ELISA X3 results. All samples from boars (36) positive in the ELISA X3 were negative in the PCR. Six out of 635 ELISA X3 positive samples from replacement gilts were positive in the PCR., they belonged to two farms.

The ELISA X3 results indicate that both replacement gilts and boars have been exposed to PRRS virus (time of exposure was not determined). With respect to the PCR test, only two farms are certain to have the PRRS virus, because sera is not the best sample to detect the virus due to the short viraemia. Considering the results it is possible to conclude that at least two of the sampled farms have PRRS virus circulation. It is suggested that prevalence of PRRS is low. It is recommended to sequence the PCR amplifications to determine the virus strain present in the positive farms, so specific control measures like vaccination can be implemented.

Disclosure of Interest: None Declared.