The threat of an outbreak of Streptococcus suis in people from pigs in North America is miniscule.
Experts agree that the Chinese epidemic of human cases of Strep suis from pigs represents a very unique situation — and stress there is virtually no chance that the same scenario will play out in this hemisphere.
“What has happened in China is a very exceptional situation, and we have never had a situation like that anywhere else,” reports University of Minnesota Professor Carlos Pijoan, DVM.
In China, more than 200 people have been sickened by Strep suis from pigs, and about 40 people have died.
How Pig Strep Spreads in Asia
In China and other Asian countries, the chances of human cases of Strep suis occurring due to infection from pigs, the natural host for the bacterial organism, are much higher than in other parts of the world, experts agree.
That's because people with small backyard hog operations literally live in very close contact with pigs, even sharing sleeping quarters, explains Marcelo Gottschalk, DVM, professor at the University of Montreal. He is considered an international expert on strep who has studied the disease for 17 years. He operates a Strep suis research laboratory in St-Hyacinthe, Canada, which has typed the majority of the 35 known serotypes of strep.
Gottschalk, who is serving as a consultant to the World Health Organization on strep problems in China, says the culture in poor regions of that Asian country sometimes results in farmers not sending hogs to slaughter. Instead, they slaughter and process the pigs themselves and either eat the meat or share it with neighbors.
“These people are frequently seen eating and handling diseased animals, which is not the case in Canada or the United States,” he notes.
Some pigs that died from strep are also consumed by poor Chinese farmers and their families, adds Pijoan. This raises the level of concern for human infection because strep organisms multiply very rapidly once an animal has died, he comments.
Pijoan suggests the Chinese cases may be the first ever reported where people have died as a result of eating meat infected with strep.
All other human cases of strep have been due to infected wounds, most commonly found in slaughterhouse workers.
Gottschalk published a paper on Strep suis in 2004 in the Journal of Swine Health and Production in which he reported that the first human case of Strep suis was described in Denmark in 1968. Since then, nearly 200 human cases have been documented in many parts of the world. Strangely enough, only a few cases have been reported in Canada and none in the United States. He believes lack of adequate testing may be responsible for the sparseness of cases in North America.
Strep suis cases in humans can produce meningitis, followed by deafness. The infection can be treated with penicillin.
Signs of Strep in Pigs
Signs of Strep suis in pigs include loss of coordination followed by convulsions, adds Sandy Amass, DVM, Purdue University. Strep also can produce swollen joints in pigs. Usually only 1-2 pigs in a pen are affected. Many pigs in a pen can be affected following an outbreak of porcine reproductive and respiratory syndrome.
Pigs commonly get colonized for strep at birth and harbor it in their tonsils throughout their lives, says Amass. Strep can be recovered in urine, saliva, feces, vaginal fluids and lungs of pigs. Treatment is with broad-spectrum antibiotics.
Amass and Gottschalk agree that farmers treating sick pigs or euthanizing pigs should wear gloves, not handle tissues from sick pigs, and wash hands afterwards.
Of the 35 known serotypes of strep, only type 2 commonly infects pigs and poses a threat to humans, says Gottschalk. As with many diseases, people with compromised immune systems are at highest risk.
“We believe that the Chinese strain of strep is a very virulent strain, but even if it did ever reach America, the impact would never be the same, because the way of life of Asian countries is completely different,” emphasizes Gottschalk.
Though strep is a very common organism in pigs, chances of humans contracting the organism remain very slim, he says. Unlike viruses, such as avian influenza, bacterial diseases are transmitted at very low rates. And unlike viruses, only pig-to-human transmission is known to occur with strep. There has never been a documented case of human-to-human transfer of Strep suis, says Gottschalk.
The Canadian researcher notes one of his colleagues is traveling to China to work with the Centers for Disease Control to find out what is different about the Chinese strains of Strep suis in pigs.