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China on Pig-Borne Disease Alert

Posted on: Tuesday, 16 August 2005, 18:00 CDT

A strange disease caused by pig-borne bacteria streptococcus suis killed 39 people and sickened more than 200 of others in Southwest China recently.

Even though medical experts say human infected cases of the disease have appeared in other parts of China before, the general public knows very little about it.

What is streptococcus suis?

According to a fact sheet released by the World Health Organization (WHO), S. suis is a species of bacterium found in many parts of the world where pigs are raised.

It was first reported in the Netherlands in 1951.

In China, it used to appear in the provinces of Sichuan, Guangdong and Jiangsu, where the swine industry is important.

The bacterium is mostly adapted to domesticated pigs, habituating in their upper respiratory tract, particularly the tonsils and nasal cavities, and the genital and alimentary tracts of the animal.

The pathogenesis of S. suis infections is poorly understood around the world.

Piglets are contaminated during farrowing. They also may acquire the bacterium due to close contact with the sows, her faeces, and the surrounding structures such as pen walls and dirty soil.

However, infected pigs usually neither spread nor exhibit symptoms of the disease, even though it could result in blood poisoning, meningitis, pneumonia and arthritis in pigs.

The death rate could be as high as 80 per cent among the pigs.

Pigs reared in "suboptimal" conditions, for example in poor housing with inadequate ventilation are more susceptible to the disease, the WHO said.

In the recent outbreak of the epidemic in China, vets and medical experts have blamed it on the unsanitary conditions of small-scale pig farms, which were aggravated by abnormally hot temperatures.

For instance, in the house of Li Haiqing, a Sichuan villager who came down with the disease, his pigs were confined to a damp, dark and smelly sty across from the bedroom.

On the mossy ground sit animal droppings, sheep and chicken feed along with other rubbish strewn around, attracting flies. Just a metre away an ewe is feeding her four lambs.

Inside Li's house, it is sweltering. Bad ventilation and an unusually hot summer served to worsen the smell.

Human infection of the endemic was first discovered in the 1960s and is increasingly recognized, the WHO said.

It usually does not cause mass outbreaks, rather sporadic occurrences.

Human infection

Chinese experts believe that the recent outbreak of the disease was triggered by S. suis II, even though little is known in terms of why different strains are associated with different symptoms, or whether and why some strains may not cause disease.

Over the years, 26 new capsular types or serotypes have been ascertained, reaching a total of 35 serotypes in 1995.

Of them, serotype 2 is the most frequently recovered from diseased pigs.

This serotype is also the cause of serious infections in humans, especially in people in close contact with swine or pork products, according to several publications related to the organism.

According to Yang Weizhong, director of disease control and emergency response office of the China Centre for Disease Control and Prevention, scientists are still not sure if the fatal bacterium in China is a new variant.

People are only likely to contract the disease if they slaughter or handle pigs that are sick or have died from the infection, Yang said.

No other transmission channels, like mosquito bites, or person- to-person contact, have been found.

But infection via eating infected pork or through the mucous membrane that lines the inner surface of the eyelid and the exposed surface of the eyeball, has been suspected in some cases, the WHO said.

The Chinese health ministry's release said that individuals could be infected with the organism via contacting contaminated soil and water, but symptoms may not show.

Normally, infection in humans produces a fever and signs of meningitis including headache, vomiting, neck stiffness, intolerance of light and decreased level of consciousness, the WHO said.

Hearing loss, which is generally permanent and affects around 50 per cent of those infected, occurs due to involvement of the auditory nerve.

In the case of Wang Xingcheng, the 55-year-old man from Sichuan, lost his hearing and consciousness two days after he handled two sick hogs, his daughter said.

Also, arthritis and pneumonia are possible complications.

Diagnosis

Diagnosis is made by the recovery of bacteria from the cerebrospinal fluid, blood or joint fluid, if arthritis occurs as a result of infection.

The bacterium can be grown in culture. Polymerase Chain Reaction (PCR) can also be used to make a diagnosis.

If diagnosis is early, prompt treatment with appropriate antibiotics will lead to recovery.

Delay in treatment, however, will adversely affect survival, according to the WHO.

Another possible consequence of infection is the occurrence of toxic shock syndrome (TSS), the WHO said.

This syndrome is also associated with other streptococcal and staphylococcal infections.

This may lead to severe damage of many vital organs, including the liver, kidneys and circulatory system.

TSS is only partially responsive to treatment with antibiotics, and intensive supportive care is required.

Prevention and vaccine

If TSS occurs, the outcome is likely to be worse, the global health organization said.

Prevention of the disease in humans depends upon control in pig populations, the WHO said.

But this presents a difficult challenge to veterinary authorities and the pig industry.

The most effective way, the release said, relies on not slaughtering, handling or consuming animals that contracted or died from some unknown disease.

Sick swine ought to be buried or burned properly. Consumers are advised to purchase pork in premium markets.

The WHO said awareness should extend to everyone who prepares and cooks pork, including those doing so in their homes.

Those with open wounds should wear gloves when handling raw or uncooked pork, and all those who prepare pork should wash their hands and clean their utensils thoroughly after preparation.

Adequate cooking is also essential.

WHO also recommends that pork should be cooked to reach an internal temperature of 70 C, or until the juices are clear rather than pink.

In terms of prevention in pigs, currently, vaccines against S. suis II are available, even though the WHO said their efficacy is not fully established.

As poor hygiene is suspected as being behind the outbreak, the ministry recommended enhancing the management and hygiene in both large-scale pig farms and private sties.

If outbreak occurs, antibacterial medication could be added to animals' feed, in addition to the inoculation of pigs, the ministry said.

Source: China Daily; North American ed.

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