Scientists say the spread of the mysterious disease may be linked to wind patterns
FOR decades researchers have been trying to decipher the Kawasaki disease. First reported in 1961 in Tokyo, the disease causes inflammation of the blood vessels in children. The disease is now one of the biggest causes of acquired heart problems in children, surpassing acute rheumatic fever.
The child develops high fever, has bloodshot eyes, bright red chapped lips, strawberry tongue and swollen hands and feet. There is damage to the heart, and if untreated one-quarter of patients develop coronary artery aneurysms (balloon-like enlargement of the artery) which can lead to heart attacks.
Many theories exist about what causes Kawasaki disease. Different pathogens like bacteria, virus and even dust mites have been linked to it. “For the past 50 years, we have screened patients for every known human pathogen and remained empty-handed,” says Jane C Burns, director of Kawasaki Disease Research Center at University of California in San Diego in the US. Her team recently found that distribution of the disease is linked to an unknown pathogen which they say spreads via flowing winds.
Blowing in the wind
The team analysed three major Kawasaki disease epidemics in Japan, non-epidemic fluctuations of the cases in Japan and San Diego, and the seasonal variation of the disease in Japan, Hawaii, and San Diego. The results revealed that Kawasaki disease cases were linked to wind currents originating in central Asia and traversing the north Pacific. Dan Cayan atmospheric scientist with Scripps Institution of Oceanography in the US and co author of the study explains, “We have found that surges in the disease are associated with wind blowing from certain directions to the region in question.” The major surges in each of the study areas were linked to seasonal shift in winds that simultaneously expose Japan to winds from central Asia, and Hawaii and California to winds from the western North Pacific.
“While the evidence points out that there may be a source of the disease that emanates from Asia, we have not firmly established this as a source nor have we pinpointed such a source,” Cayan notes. It is possible that different regions may be vulnerable to Kawasaki disease bursts as they are exposed to winds which carry aerosols which harbour the pathogen, but more studies are needed to construct a true vulnerability map, he says. The results were published in the November 10 issue of Scientific Reports.
It was possible to draw an association between wind patterns and rate of Kawasaki disease cases in Japan as the country has an extensive surveillance programme. Drawing similar inferences in other countries is hampered by lack of data. “The reporting needs to happen globally, not only as a source of information but to raise awareness and understanding of the disease,” says Cayan.
The team now plans to analyse the link between wind and Kawasaki disease occurrences to better understand the time lag between the disease favourable wind episodes and hospitalisations. “We will also try to identify source regions that might reveal origin of possible pathogens and also the necessary atmospheric conditions that inject this pathogen into air currents,” he adds.
When asked whether climate change, which is affecting wind patterns around the world, could affect the distribution of the disease, Cayan said, “Climate change may well affect winds which may alter Kawasaki exposure, but this is not well studied.”
Efforts are also being made to identify the pathogen. “Researchers at Columbia University are sequencing the biome of tropospheric wind from dust samples collected from these areas. The results might be out in six to eight months,” says Burns. To understand the status of the disease in the areas where the winds originate (for example central Asia), the team has launched a study in Irkutsk, Siberia. The team has initiated a research—WIND study (West Coast Investigation of Kawasaki)—to find why the disease is more prevalent in coastal areas. “This type of active surveillance has never been done,” Burns says. She contends that the agent could be a virus based on the behaviour of the disease.
“The main issue is to understand what causes the disease and develop therapeutic and preventive interventions,” says Eugene Shapiro, an epidemiologist at Yale University in the US. His team had in 2005 identified a coronavirus in the respiratory tract of infants with the disease and said this could be the causal organism. But no other researches could establish the link. Also, researchers at Northwestern University in the US have identified what looks like virus particles in upper airway of such patients.
Kawasaki disease cases on the rise
Burns’ team has also collected a set of new data on the incidence of the disease from around the globe and is analysing it. Initial results show that the incidence varies from about eight in 100,000 children in Scandanavian countries to a high of 215 cases in 100,000 children below the age of five in Japan.
In India, the estimated numbers of new Kawasaki cases per year are around 250,000. The first documented case was reported in 1977. In Kerala, more than 1,000 cases are registered, reveals Saji Philip, secretary general of the Kawasaki Disease Foundation India in Kerala. Registered cases are slowly emerging in major cities, he says. Researchers at the Post Graduate Institute of Medical Education and Research at Chandigarh, analysed data of Kawasaki patients from January 1994 to December 2008 and calculated the yearly incidence of the disease. They found that the incidence increased from 0.51 cases per 100,000 children below 15 years of age in 1994 to 4.54 cases per 100,000 in 2007. Disease peaks were seen in May and October. It was observed that children as old as 15 were affected by the disease. In other countries only children up to the age of five have been affected by the disease.
Philip points out that getting the figure of affected children is important because the treatment is expensive and help from government is needed. The standard therapy is Intravenous immunoglobulin (IVIG) and aspirin. “A five gram vial of IVIG costs Rs 16,000 and the normal dose of IVIG in Kawasaki disease is two gram per kg body weight every 24 hours,” he says.