An international team of climate and medical researchers has found evidence that cases of the childhood illness known as Kawasaki disease are linked to large-scale wind currents that track from Asia to Japan and also traverse the North Pacific.
Kawasaki disease (KD) is a severe childhood disease that many parents, even some doctors, mistake for an inconsequential viral infection. In fact, if not diagnosed or treated in time, it can lead to irreversible heart damage. After 50 years of research, including genetic studies, scientists have been unable to pinpoint the cause of the disease.
The team was organized by Jane C. Burns, professor and chief, Division of Allergy, Immunology, and Rheumatology at UC San Diego School of Medicine's Department of Pediatrics and Rady Children's Hospital-San Diego and included Dan Cayan, a climate researcher at Scripps Institution of Oceanography, UC San Diego.
Signs of KD include prolonged fever associated with rash, red eyes, mouth, lips and tongue, and swollen hands and feet with peeling skin. The disease causes damage to the coronary arteries in a quarter of untreated children and may lead to serious heart problems in early adulthood. There is no diagnostic test for Kawasaki disease, and current treatment fails to prevent coronary artery damage in at least one in 10 to 20 children and death in one in 1,000 children.
While seasonality of the disease has been noted in many regions - particularly in Japan, the country of highest incidence for KD - the answer to why epidemics and fluctuations in KD occur has been elusive. A study of KD cases in Japan since 1970 showed three dramatic nationwide epidemics, each lasting several months and peaking in April 1979 (6,700 cases), May 1982 (16,100 cases) and March 1986 (14,700 cases). These three peaks represent the largest KD epidemics ever recorded.
To investigate a possible influence from large-scale environmental factors, Cayan and Xavier Rodo and Joan Ballester of the Institut Català de Ciències del Clima and the Institució Catalana de Recerca (IC3) in Barcelona, Spain, investigated a set of atmospheric and oceanographic measures, which revealed a link to pressure patterns and associated wind flow from the surface to mid-tropospheric atmospheric levels during the summer months prior to onset of the epidemics.
"The Japanese dataset revealed that a low number of KD cases were reported prior to the epidemics, a period coinciding with winds from the south which blew across Japan from the Pacific Ocean during the summer months," said Rodo, the study's first author. "However, the numbers rapidly mounted all over Japan when winds turned and blew from the northwest, a trajectory from the Asian continent After the peaks, the winds again shifted, blowing from the south when the number of cases again decreased."
"Importantly, subsequent to the three epidemics, years with increased numbers of Kawasaki disease cases in Japan were significantly associated with enhanced local northwesterly winds, as a result of low pressure centered to the north," said Cayan.
To assess whether such variations in wind patterns were associated with KD case fluctuations on the other side of the North Pacific, similar analyses were conducted for San Diego. According to the scientists, the atmospheric connection from continental Asia to Japan and San Diego is intermittent and can take different routes. However, it was possible from their analysis to identify the major anomalous yearly peaks of KD cases occurring in San Diego from 1994 to 2008 as belonging to two main atmospheric configurations.
In fact, the major fluctuations in KD case numbers in Japan, Hawaii and San Diego were linked to a seasonal shift in winds that exposed Japan to air masses from Central Asia. One key pattern simultaneously exposed Hawaii and California to air masses from the western North Pacific.
"The linkage to the wind currents, which can cross the Pacific in less than one week, may explain why KD case numbers recorded in Japan, San Diego and Hawaii show a nearly synchronized seasonal peak in disease activity from November through March," Rodo said.
Burns said that the findings could be significant in efforts to isolate the cause of the disease.
"It could be that an infectious agent is transported across the ocean by strong air currents developing in the upper troposphere," she said, adding that while this would seem the most plausible explanation for the findings, the role of pollutants or other inert particles must be considered.
These hypotheses are currently being investigated. A research aircraft carrying an engineer from the Catalonian team and a custom-built air sampling apparatus collected tropospheric air samples from over Japan in March and the entire biome of the tropospheric dust collection is being sequenced in the laboratory of Ian Lipkin at Columbia University in New York City. Lipkin is one of the leading "molecular detectives" who uses sequencing to find new infectious agents. On the other side of the U.S., teams of pediatric doctors from hospitals from California to Alaska and Hawaii have initiated real-time reporting of KD cases via the web to Scripps where Cayan and his team are analyzing cases in relation to regional climate and tropospheric wind patterns.
While links between human respiratory disease and large-scale dust transport are well-documented, to date there has been no evidence of long-range wind transport of an infectious agent causing human disease.
Additional contributors to the study include Marian E. Melish, John A. Burns School of Medicine, Kapiolani Medical Center, Honolulu, Hawaii; Yoshikazu Nakamura and Ritei Uehara, Jichi Medical School, Japan.
Funding for the study was provided in part by a grant from the National Heart, Lung and Blood Institute, part of the National Institutes of Health, by the NOAA Regional Integrated Sciences and Assessments program, and by a grant to Rodo from La Marató de TV3 Foundation.