CASE NOTES
Streptococcus suis infection in humans - an emerging disease?
Eliz Braddon, DV Young RLPB
Posted Flock & Herd August 2008
Introduction
Strep. suis infection is common in most pig herds. It can be readily isolated from clinically healthy pigs, where it may be carried in the tonsils, nose, alimentary and reproductive tract. Transmission can occur transvaginally at birth from an infected sow, via the umbilical cord, through fighting or by contact with contaminated animal husbandry equipment.
The disease in pigs is caused by S. suis serotype 2. It has commonly been isolated from cases of meningitis, arthritis, septicaemia, endocarditis, pericarditis and rhinitis. It can affect any age of pig, but disease is most common in young suckling or weaned pigs rather than finishers.
The first human case of S. suis was reported in Denmark in 1968. Since then, there have been around 415 cases recorded. They have been reported from most countries, including The Netherlands, United Kingdom, France, Hong Kong, China, Thailand, Taiwan, United States and Canada. The largest outbreak was in China in 2005 where 215 cases were suspected in one outbreak.
Humans considered most at risk are those that handle live pigs, carcasses or eat undercooked pork. Farm workers, butchers and abattoir personnel are particularly at risk. Clinical syndromes seen in human cases include septicaemia, meningitis, arthritis, endocarditis and in the case of the Chinese outbreak, Strep Toxic Shock-Like Syndrome (STSS). The Chinese outbreak resulted in 38 deaths. In most other reports, deaths were uncommon. Transmission from pigs to humans is most likely through open wounds and possibly via the mucous membranes (e.g. aerosol to eyes/ mouth) though this has yet to be definitively proven.
As S. suis type 2 is easily inactivated by liquid soap in a 1:500 dilution in less than 1 minute, good hygiene and covering wounds will significantly reduce the risk of infection to humans.
INVESTIGATIONS AND FINDINGS
There have now been two human cases of infection with S. suis in the Young district of NSW. This is the first time human cases of infection with S. suis type 2 have been recorded in Australia. Both of these cases have been associated with the one large local piggery housing around 2450 sows. This piggery is well managed and has a high commitment to the welfare of both pigs and personnel.
The first case occurred in September 2006. This was a female in her mid-40s who worked at the piggery as a unit manager. She developed a vegetative endocarditis requiring heart valve replacement. No prior skin wounds or other illness was thought to have preceded the infection. She was a smoker.
The second case in a male in his mid-40s occurred in January 2008. He worked for a livestock transport company that primarily carted pigs from this piggery. A wound on his arm may have predisposed to infection and the subsequent development of endocarditis and meningitis. He was also a smoker.
The last diagnosis of pig disease attributable to S. suis type 2 in the piggery was in 2001. In recent years, the disease has not been diagnosed in the pigs.
CURRENT WORK
The objectives of ongoing work are to isolate the human case strain from the local piggery, so as to link occupational exposure to the human cases. Other piggeries across the district are also being sampled in an attempt to determine how widespread this particular S. suis strain may be.
A collaborative effort by the piggery staff and management, University of Sydney PhD students, James Chin (EMAI), DPI and Young RLPB to try to understand more about this zoonotic disease is underway. The piggery has been sampled in an attempt to isolate the same Strep. suis that caused the human cases. Other pigs from another local piggery are also being sampled at the Burrangong abattoir.
The protocol followed to date has been to sample live weaners and growers by taking duplicate swabs from nostrils, vagina and rectum. Forty-eight pigs from across 3 Units on the local piggery were sampled on 17/3/08.
The author swabbing the rectum of a weaner on a local piggery
A single tonsillar swab is also being taken from pigs sourced from local piggeries at the Burrangong abattoir. These are being taken between stunning and bleeding. Sampling of 13 pigs taken from another large local piggery occurred on 18/3/2008.
Nasal swabs were also voluntarily taken from 5 piggery workers and 1 RLPB vet. These swabs tested negative to S. suis isolates. The piggery workers were the 3 unit managers who spend their entire day with pigs, the other 2 were a maintenance worker and the piggery manager, who also spend considerable time with pigs. The RLPB vet was only exposed to the pigs for a short period at the time of sampling.
Opportunistic sampling may be performed on fresh dead pigs from the local piggery in the near future. This will depend on the results of the current testing. More abattoir sampling will take place if such sampling is deemed to be effective.
UPDATE
As at 31/10/2008, the tonsillar swabs taken from the Burrangong abattoir have provided no growth of S. suis strains similar to the human isolates. However, there have been 7 isolates from the local piggery. On initial screening these appear to be similar to the human case strain. More specific DNA typing is occurring to investigate the relationship between these isolates further. Also additional testing from a third piggery source has been undertaken. Those samples are yet to be cultured.
Another human case, a 41 yo male pet food processor in Victoria, was recently published. The isolate from this case matches those from the humans at Young. There is no known link between the Victorian case and the Young cases. Human health officials have been contacted to try to determine the true prevalence of S. suis cases in humans as anecdotal reports suggest it may be more common than currently thought. This investigation is ongoing.