zoonoses and communicable diseases common to ... - PAHO/WHO

262 BACTERIOSESInfection caused by S. suis type 2 is a true zoonosis. It is a highly occupationaldisease among those who breed pigs or participate in slaughtering, processing, ormarketing them. Man contracts the infection primarily through skin lesions.The infection in swine is widespread in areas where these animals are bred. In anendemic herd, both sick and healthy pigs carry the agent in their nasal cavities andtonsils. The percentage of carrier animals can reach 50% or more of the herd duringoutbreaks and fall to only 3% when there are no clinical cases. Carrier status can lastfor at least 45 days and may persist in animals treated with penicillin (Clifton-Hadley and Alexander, 1980). Among swine, the infection is transmitted through theair and possibly through the digestive route as well. Pigs can also be carriers of S.suis in the vaginal canal and piglets can become infected during delivery (Robertsonet al., 1991).Animals can also transmit groups G, L, and M to man, but the epidemiology ofthese cross-infections has not yet been elucidated.Role of Animals in the Epidemiology of the Disease: Swine are the reservoirand source of S. suis infection in man. Animals do not act as maintenance hosts forS. pyogenes, but can sometimes cause important epidemic outbreaks by contractingthe infection from man and retransmitting it by means of contaminated milk. Thereis no firm evidence that animals play any significant role in the transmission ofgroup B streptococci causing neonatal sepsis. Raw cow milk can be a source ofgroup C streptococcal infection in humans.Diagnosis: If milk is suspected as the source of an epidemic outbreak in man, anattempt should be made to isolate the etiologic agent. Obviously, a correct identificationof the agent is required. From either a human or animal source, it is advisableto identify the serogroup of streptococci involved, and to establish the species wheneverpossible. However, few laboratories have the human and material resourcesnecessary for this task.A method has been described for identifying pregnant women with heavy colonizationof the genital tract by group B streptococci (Jones et al., 1983). The goalof this procedure is to start treating the newborn with drugs immediately after birthto reduce morbidity and mortality due to neonatal sepsis caused by group Bstreptococci.Infection by S. suis should be suspected if the patient presents the clinical manifestationsdescribed and his or her occupation involves contact with swine or theirby-products. Culture, isolation, and typing can confirm the diagnosis.In swine, definitive diagnosis also depends on isolation and identification of theagent. In endemic herds, the symptomatology may be sufficiently clear to make aclinical diagnosis during new outbreaks. In a study conducted in Quebec (Canada)with 1,716 weaned pigs belonging to 49 herds and 23 control herds, nasal and tonsilsamples were taken with swabs. The samples were cultured in a brain-heart infusionbroth, strengthened with a supplement selective for Streptococcus and 5% anti-S. suis type 2 serum developed in goats. After the diameter of the precipitation zonewas measured in 539 isolates, serum plate agglutination was used to identify isolatesof S. suis serotype 2. This method successfully identified 93.1% of the cultures isolatedusing the diameter of the precipitation zone as the sole criterion. Specificitywas 94.5% and relative sensitivity was 88.7% (Moreau et al., 1989).