Streptococcus suis may be emerging as a human pathogen

Increasing incidence of Streptococcus suis transmitted from pigs to humans has recently been reported in several countries.

Review data revealed that up to 80% of healthy pigs may be carriers of a variety of serotypes of S. suis. Morbidity from the infection in pigs can range from less than 1% to greater than 50% but rarely exceeds 5%, according to the researchers.

An article published in 2007 indicated that there had been 409 cases of human S. suis starting in 1968 when the first case was reported in Denmark. That number has now exceeded 700 cases.

There were 151 cases of human S. suis in southern Vietnam during a recent 10-year period, according to the researchers. An outbreak in Sichuan Province, China in 2005 infected 215 people and killed 38.

The male-to-female ratio of S. suis cases ranges from 3.5:1.0 to 6.5:1.0. The rate among slaughterhouse workers and pig breeders in developed countries is approximately 3.0 cases per 100,000 population. For butchers, it is 1.2 cases per 100,000 population.

Meningitis is the most common clinical manifestation of S. suis. Skin findings including petechiae, purpura and ecchymoses may be found in 6% to 31% of patients. Up to 50% of patients may experience subjective hearing loss at presentation or a few days after presentation.

Clinicians should treat S. suis using a similar protocol as bacterial meningitis, according to the researchers. – by Rob Volansky

Clin Infect Dis. 2009;48:617-625.

This article provides a timely review of epidemiological, clinical and microbiologic features of another important emerging zoonotic disease. Like many other zoonotic pathogens, S. suis was first recognized as a pathogen by veterinarians, in this case following outbreaks in piglets in 1954. Fourteen years later, the first human cases were diagnosed, providing yet another reminder of the importance of communication and collaboration among the veterinary and human medical and public health communities. The One Health Initiative emphasizes such communication.

The disease in humans, most often manifested as meningitis or sepsis, and most often caused by serotype 2 strains, appears to be associated primarily with occupational exposure to pigs or pork products. Although additional epidemiological studies are needed, the disease also may be associated with preparation and ingestion of pork products, particularly those that are undercooked. Although the agent has a global distribution, human cases have been reported primarily in China, Vietnam and Thailand. Pork consumption and pig density are both high in these countries, suggesting that increasing demand for pork and changes in livestock-rearing practices may be important contributors to the emergence of the disease.

– James Hughes, MD

Infectious Disease News Editorial Board member