Credit Japan’s NARO (National Agriculture and Research Organization)
# 6993
This morning Hong Kong’s CHP is reporting a relatively rare, fatal infection from S. suis in an 85 year old man. This adds to a growing list of recent news stories about this emerging zoonotic pathogen.
While not the sort of stuff that pandemics are made of, S. suis may have more of an impact on human health than is currently appreciated.
Streptococcus suis is a Gram-positive bacterium, well entrenched in global pig populations, capable of causing serious (even fatal) infection in humans.
With 35 known serotypes - S suis represents a large and diverse species of bacteria – many of which are carried asymptomatically by healthy pigs.
Serotypes 1-8 are most often associated with disease in pigs, and among humans, infection is most commonly by serotype 2.
The Merck Veterinary Manual states:
S suis is found in the upper respiratory tract, particularly the tonsils and nasal cavities, and the genital and alimentary tracts of pigs.
Clinical infections are seen mainly in weaners or growing pigs and less frequently in suckling piglets. S suis has been isolated from a wide range of animal species, eg, cattle, sheep, goats, horses, and birds, as well as humans. Its presence in the environment is transitory.
Last month, the Canadian Swine Health Intelligence Network announced Strep Suis Identified as Top Reason for Calling Vets to Swine Farms.
In 2007 The Lancet carried the following report identifying S. suis as an important emerging pathogen.
Streptococcus suis: an emerging zoonotic pathogen.
Lun ZR, Wang QP, Chen XG, Li AX, Zhu XQ.
Abstract
Streptococcus suis is a major porcine pathogen worldwide, and can be transmitted to human beings by close contact with sick or carrier pigs. S suis causes meningitis, septicaemia, endocarditis, arthritis, and septic shock in both pigs and human beings, and mortality is high.
Human infection with S suis occurs mainly among certain risk groups that have frequent exposure to pigs or pork. Outbreaks of human S suis infection are uncommon, although several outbreaks have occurred in China in recent years.
In July, 2005, the largest outbreak of human S suis infection occurred in Sichuan province, China, where 204 people were infected and 38 of them died. There have been 409 cases of human S suis infection worldwide, most of which have occurred in China, Thailand, and the Netherlands, and these infections have led to 73 deaths.
More recently, in Frontiers in Microbiology, researchers suggested that S. suis may serve as an important antibiotic resistance reservoir, and may be contributing to the spread of resistance genes to other bacteria.
Streptococcus suis, an Emerging Drug-Resistant Animal and Human Pathogen
Claudio Palmieri, Pietro E. Varaldo, and Bruna Facinelli
Abstract
Streptococcus suis, a major porcine pathogen, has been receiving growing attention not only for its role in severe and increasingly reported infections in humans, but also for its involvement in drug resistance.
Recent studies and the analysis of sequenced genomes have been providing important insights into the S. suis resistome, and have resulted in the identification of resistance determinants for tetracyclines, macrolides, aminoglycosides, chloramphenicol, antifolate drugs, streptothricin, and cadmium salts.
Resistance gene-carrying genetic elements described so far include integrative and conjugative elements, transposons, genomic islands, phages, and chimeric elements. Some of these elements are similar to those reported in major streptococcal pathogens such as Streptococcus pyogenes, Streptococcus pneumoniae, and Streptococcus agalactiae and share the same chromosomal insertion sites.
The available information strongly suggests that S. suis is an important antibiotic resistance reservoir that can contribute to the spread of resistance genes to the above-mentioned streptococci. S. suis is thus a paradigmatic example of possible intersections between animal and human resistomes.
Confirmed human infection with Streptococcus suis in North America remains very rare, but there are at least 4 known cases in the United States. Recently the CDC's EID Journal carried a letter detailing Streptococcus suis Meningitis in Swine Worker, Minnesota, USA.
To the Editor: Streptococcus suis is a major bacterial pathogen in swine worldwide. Historically, cases in humans have occurred sporadically, mostly in Asia (1,2). However, an outbreak in China involved 215 human cases and 39 deaths (3). Only 3 human cases of S. suis disease were documented in the United States before 2011: 2 domestically acquired cases in New York and Hawaii, and 1 case in a person in California who was probably exposed in the Philippines (4). We describe a case of S. suis disease in a swine worker in Minnesota, USA.
This year we’ve seen a substantial number of cases of S. suis out of Vietnam, as evidenced by this story from Thanh Nien News.
Say no to pig blood pudding, doctors advise as swine bacteria kill 4
Last Updated: Friday, March 01, 2013 10:10:00
Vietnamese Lunar New Year festivities in February, during which many pigs were slaughtered and served, sometimes raw, sent at least 12 people to hospital, with swine bacteria killing four.
Two died in hospitals and two others died at home in central Vietnam.
A source from the National Hospital of Tropical Diseases in Hanoi last week said they received 16 people infected with the Streptococcus suis bacteria, a pork-based pathogen, since the beginning of this year, including nine during the ten days of the festival that began on February 10.
And from another recent EID Journal letter we get an idea of just how prevalent this infection is in Vietnam:
Streptococcus suis and Porcine Reproductive and Respiratory Syndrome, Vietnam
In Vietnam during September 2006–November 2007, the carrier rate of S. suis among slaughterhouse pigs was 41% (222/542); SS2 was the most frequently identified serotype in 14% (45/317) of S. suis isolations (4)
All of which leads to today’s story out of Hong Kong, that unfortunately, has not determined the route of infection.
A case of Streptococcus suis infection under investigation
The Centre for Health Protection (CHP) of the Department of Health is today (March 9) investigating a fatal case of confirmed infection by Streptococcus suis (a kind of bacteria isolated from pigs).
The patient is a 85-year-old man with an underlying medical condition. He developed fever and vomiting on March 2 and was admitted to Kwong Wah Hospital on March 3. He was diagnosed to have septicaemia. His condition deteriorated on March 4. He was transferred to intensive care unit on the same day and passed away a few hours later.
His blood grew Streptococcus suis.
A CHP spokesman said the patient had no recent travel history. His home contact did not have any symptoms.
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Ends/Saturday, March 9, 2013
Issued at HKT 16:25
While seemingly a minor concern in North America, a study conducted in 2008 at the University of Iowa - by Tara C. Smith (Aetiology Blog) et al. – suggests that this bacterial infection may be more prevalent than we know.
Occupational Exposure to Streptococcus suis among US Swine Workers
Tara C. Smith, Ana W. Capuano, Brenda Boese, Kendall P. Myers, and Gregory C. Gray
Abstract
Despite numerous cases of human infection with Streptococcus suis worldwide, human disease is rarely diagnosed in North America. We studied 73 swine-exposed and 67 non–swine-exposed US adults for antibodies to S. suis serotype 2.
Serologic data suggest that human infection with S. suis occurs more frequently than currently documented.
The authors provide two reasons why this bacterial infection may be going under reported in North America.
One possibility is under diagnosis or misdiagnosis, rather than a true absence of the disease.
A second possibility is that S. suis strains colonizing swine in the United States may be less virulent than Asian strains and therefore unlikely to cause overt human disease even when transferred between species.
Should the second possibility prove correct, then the potential of seeing a more virulent strain emerge outside of Asia cannot be discounted.
All of which makes S. suis both a fascinating and important pathogen to watch.
