Introduction

The list of secondary pathogens that can be associated with PRRS ( Porcine Reproductive and Respiratory Syndrome) problems is extensive: Actinobacillus pleuropneumoniae, Salmonella choleraesuis, Streptococcus suis, Haemophilus parasuis, typical and atypical strains of Influenza virus, porcine respiratory Corona virus, Pneumocystis carynii, etc. Most of these organisms can cause problems by themselves. However, they are frequently present in herds where no or few clinical signs are observed, as if they were in equilibrium with the immune defense system of the animals. When PRRS outbreaks occur, it seems that the virus may frequently destroy this equilibrium and give secondary pathogens the opportunity to, at least temporarily, "win the battle".

This presentation will very briefly describe the conditions caused by some of the most significant of these secondary pathogens, how to identify them and say a few words about their potential implications for humans.

Actinobacillus pleuropneumoniae

This bacteria, of which 12 serotypes have been identified so far, causes porcine pleuropneumonia. Pigs affected with this disease may show fever, dyspnea, coughing and mortality rates, if it is not treated properly, can go high. Vomiting can also be observed, and this is a feature that is not frequently seen with other respiratory pathologies. In very severe cases, individual animals sometimes have blood spilling from their mouth or nose before death. After death many pigs can have a pink to red froth coming from the same orifices. If an autopsy is performed, the pulmonary lesions observed are quite characteristic.

Identification: lungs have to be submitted to the laboratory. Isolation of the organism is not difficult and serotyping as well as sensitivity results (to antimicrobials) can be obtained at the same time.

Human implications: there are no cases reported in the literature of human infection. However, Actinobacillus pleuropneumoniae serotype 5 has been isolated once from the wound of a producer that had been bitten by a boar.

Salmonella choleraesuis

This organism causes septicemic salmonellosis. It is one of the rare diseases of swine where both dyspnea (thumping) and diarrhea can be observed. Another feature of this pathology is that some of the affected pigs may show cyanosis (blue coloration) of the extremities (ears, snout, bottom part of the legs). Although sudden deaths may sometimes be observed, usually pigs will gradually lose condition and take a while before they die. If the treatment is not efficacious, both the mortality rate and the number of cull pigs can be high.

Identification: lungs, lymph nodes and liver are specimens of choice to bring to the laboratory. The organism is not difficult to isolate and sensitivity results are obtained at the same time.

Human implications: on extremely rare cases Salmonella choleraesuis has affected humans. Interestingly, the people affected were usually not workers of the swine industry. The mortality rate in these cases has been very high.

Streptococcus suis

Thirty-five serotypes of Streptococcus suis have been identified so far and this number will soon get to 40. Serotype 2 is the most frequently isolated and the most important. Virulence differs greatly between serotypes and between isolates of the same serotype. This organism may be associated with many types of infections, the most frequent being septicemia (infection of the blood), meningitis, arthritis and polyserositis. It is often isolated from pneumonia cases, but it is believed to be complicating rather than causing this lesion. Clincical signs vary according to the systems or organs involved. For example, in cases of meningitis pigs will often lay on one side and paddle, while those affected with polyserositis may show dyspnea and stunting.

Identification: specimens to submit also depend of the systems involved (head if meningitis, joints if arthritis, lungs, liver and lymph nodes if septicemia or polyserositis). The bacteria is not difficult to isolate but more than one strain can be present on the same pig. This has to be taken in consideration when comes time to analyze serotyping or sentivity results. The strain from which the results are obtained may not be responsible for the problems observed.

Human implications: this organism can affect people and the cases reported in the literature generally implicate, but not always, workers who have contacts with pigs (producers, veterinarians, etc.) or pig products (slaughter house employees, butchers, etc.). There is no need to dramatize. It is still a very rare infection. It can, however, be serious. In fact, Streptococcus suis can cause, among other things, meningitis, which is sometimes fatal. Furthermore, about 50% of the survivors are left with deafness. Serotypes 2, 4 and 14 have been isolated, so far, from humans.

Haemophilus parasuis

The classical condition associated with this organism is Glasser's Disease, which is manifested by some or all of the following lesions: polyserositis, meningitis and arthritis. Again the clinical signs will depend of the systems affected. If there is arthritis, pigs will have swollen joints while if meningitis is present, nervous signs like paddling may be observed. Serotypes 2, 4, 5, 12, 13, and 14 are the most frequently isolated. All serotypes and strains do not have the same virulence.

Identification: same specimens as for Streptococcus suis and again more than one strain can be present on the same pig.

Human implications: none, so far.

Take-Home Message

PRRS outbreaks are frequently complicated by secondary pathogens.

Most of them can easily be identified if the proper submissions are sent to the laboratory.