Streptococcus suis is an opportunistic bacterium which usually colonises the upper respiratory tract of adult pigs without causing any disease. It can, however, be the reason for severe disease in piglets, and it is known to be responsible for large economical losses in the swine industry.
Streptococcus suis is transmitted to humans through close contact with infected pigs or pork, and people in occupational contact with pigs (e.g. pig farmers, abattoir workers, veterinarians) represent the principal risk group for the disease. The pathogen can cause serious systemic infections, most commonly meningitis and sepsis. Other disease manifestations include pneumonia, arthritis, endocarditis, and streptococcal toxic shock-like syndrome (STSS). Deafness is reported as common sequelae of the disease.
The majority of the 700 human cases which have been reported since 1968 originated from Southeast Asia, i.e. China, Vietnam, and Northern Thailand. Streptococcus suis meningitis is currently the second most common cause of acute bacterial meningitis in adults in Thailand. Several sporadic cases have also been reported from European countries. Outbreaks of human infections mainly occur in low-income countries with intensive pig production, which is largely due to close contact of humans to pigs and lack of awareness of the disease within the population at risk.