Researchers call for greater focus on surveillance and genomics.
An outbreak of hand, foot and mouth disease in China, which since January has killed 19 children and made nearly 42,000 ill, has researchers calling for a better surveillance system to detect the disease and for action to speed up vaccine development.
"The situation of preventing and containing hand, foot and mouth disease is very serious at the moment," Deng Haihua, spokesman for China's health ministry, said last week. More cases are expected, as the disease normally peaks between May and July. In the absence of a drug treatment, the ministry is focusing on prevention and containment.
The outbreak is the latest in a series to have hit China in recent years, caused by a fast-spreading virus called enterovirus 71. "The persistence of enterovirus 71 outbreaks in China is a wake-up call," says Jane Cardosa, a virologist at the University Malaysia Sarawak in Kota Samarahan. In 1997, Sarawak saw the first outbreak of hand, foot and mouth disease in the Asia-Pacific region.
The disease causes flu-like symptoms, along with rashes on the hands and feet, and mouth ulcers. It can be caused by many types of human enterovirus belonging to the Picornaviridae family, which are mainly transmitted through faecal or oral routes. Although normally mild, the disease can be life-threatening: some viruses, particularly enterovirus 71, can cause inflammation of the brain stem, resulting in heart failure and fluid accumulation in the lungs.
In 1997 in Sarawak, more than 2,600 cases of the disease were reported and 29 people died. The next year in Taiwan, there were 129,000 reported cases and 78 deaths. In mainland China, the first reported case was in Shenzhen, Guangdong province, in 1999. At first, outbreaks were local and there were no reported fatalities (L. Li et al. J. Clin. Microbiol. 43, 3835–3839; 2005). But since 2004, the outbreaks have become more severe and widespread, says Xu Wenbo, an infectious-disease expert at the Beijing-based China Center for Disease Control and Prevention.
“The persistence of enterovirus 71 outbreaks in China is a wake-up call. ”
In May 2008, the country's health ministry added hand, foot and mouth to its category 'C' of notifiable diseases, meaning that all diagnosed cases must be reported through a national web-based system for disease surveillance, and took measures to streamline reporting requirements. The ministry also vowed to take a tough stance against cover-ups and last month sacked four health officials in Henan province for concealing the number of infections and deaths.
This year, enterovirus 71 has caused nearly all of the laboratory-confirmed cases in two hot-spots, the provinces of Henan and Shandong. Xu suspects that the disease's increasing virulence may be due to a genetic change in the circulating virus strain. Before 2004, the predominant strain was called C4b; since then, a different strain, C4a, has been most common (Y. Zhang et al. J. Clin. Virol. 44, 262–267; 2009).
What caused this switch isn't clear, says Xu, as little is known about the genetics and transmission trends of the fast-mutating virus. Most studies have been clinical, aimed at, for example, identifying the strains behind a given outbreak and the disease's clinical features, especially when there are neurological complications. Many researchers say it is time to step up efforts to understand the basic biology of enterovirus 71 to speed vaccine development.
In a major push financed by the Chinese health ministry and the Center for Disease Control and Prevention, Xu and his colleagues measured the infection rate in adults and children during last year's outbreak and analysed stool samples and throat swabs taken from more than 18,000 patients. Preliminary results suggest that the infection rate is alarmingly high, meaning that there are large populations of virus carriers who do not show any symptoms of the disease.
Experts are divided as to how worried the world should be about the virus. Tom Solomon, a neurologist at the University of Liverpool, UK, argues that enterovirus 71 infection is underappreciated on a global scale and may pose a bigger risk to public health than is currently thought. But Hans Troedsson, the World Health Organization's representative in China, says "there is no cause for alarm". The public-health impact of hand, foot and mouth disease, including cases caused by enterovirus 71, is no more serious than other common childhood diseases, he says.
Troedsson thinks that the recent apparent increase in enterovirus 71 infection might be due to higher reporting rates rather than an increase in disease prevalence. "We will closely monitor the situation and decide polices accordingly," he says.
About this article
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