Virologists are working to slow the spread of the largest recorded outbreak of chikungunya, a relatively unknown mosquito-borne disease that has swept through the island of Reunion
, and was recently reported
in India. Some researchers are focusing their efforts on a promising, early-stage vaccine developed by the U.S. military.
The French government
, under media fire for alleged slow response to the epidemic, has formed a special panel
to coordinate research on emerging diseases, especially chikungunya. The World Health Organization
is sending a team to the region.
Named for the Swahili for "that which bends up," chikungunya is an alphavirus vectored by culicine mosquitoes, causing high fever, joint pain, and rarely neurological and hemorrhagic symptoms. Isolated in 1953 in Tanzania, the virus likely originated in a tropical African forest cycle involving wild primates and mosquitoes, spreading via Aedes aegyptii
and others to urban Africa and Asia, causing sporadic epidemics in Thailand and Indonesia.
In early 2005, more than 5,000 cases were reported in the Comoros Islands off East Africa. The outbreak spread to the French Indian Ocean island of Reunion, where it has, as of earlier this week, infected 14% of the population, causing 130,000 cases and contributing to 77 deaths, according to Martin Guespereau, an advisor to the French Health Minister. "No one knows why the unexpected gravity of the epidemic in Reunion," he told The Scientist
. The virus has already surfaced in Madagascar and India, and efforts are underway to prevent its spread to the French Antilles and Guiana in South America, he said.
Molecular virologist Ann Powers, Chief of Alphavirus and Bioterrorism Research with the CDC's Division of Vector Borne Diseases in Fort Collins, Colorado, visited the Comoros Islands last year. "You could walk in any part of town and meet people who were either affected or whose family members were affected," she said.
, a vector biologist with the Center for Biodefense & Emerging Infectious Diseases at the University of Texas Medical Branch in Galveston, told The Scientist
the virus is "kind of strange" because it doesn't seem to have animal reservoirs. Instead, chikungunya circulates between people and diurnal mosquitoes, infecting the mosquitoes
when they bite people carrying high levels of the virus in their blood.
In the mid-1980's, scientists at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID
) developed the only known chikungunya vaccine, said Robert Edelman
, based at the University of Maryland's Center for Vaccine Development in Baltimore.
Edelman conducted the last major study of the vaccine in the late 1990s. The phase II study
of live attenuated chikungunya vaccine -- created from an isolate taken from a patient in Thailand -- involved 73 adults, 59 of them immunized by the vaccine and 14 by placebo. Fifty-seven (98%) of 58 evaluable vaccinees developed a chikungunya neutralizing antibody by day 28; 85% were seropositive one year after immunization. "It's a very promising vaccine," and well-tolerated, Edelman told The Scientist
Work on the vaccine diminished in recent years, said Edelman, adding that the U.S. Government focused on diseases more likely to threaten U.S. troops. But Edelman said the French government is taking media heat for neglecting the outbreak. "This is their Hurricane Katrina."
Discussions with the French are underway about using the vaccine developed by the U.S. military, said David Vaughn, director of the Military Infectious Disease Program at the U.S. Army Medical Research and Materiel Command in Fort Detrick, Maryland. With "tens of millions of doses" of vaccine still on hand, Vaughn said the outbreak is a chance to bring the vaccine to licensure.
Guespereau said the vaccine needs further testing, but added "we won't turn down any lead," and confirmed the government is talking to the U.S. Army. Meanwhile, without a viable vaccine, researchers continue to investigate the virus, searching for more animal vectors, and focusing on public education, symptom relief, antivirals, and destroying mosquito breeding habitats from puddles to old tires.
Links within this article
Reunion Regional Health Observatory website on chikungunya
Chikungunya - India: suspected, ProMed Mail
, February 20, 2006.
French Health Ministry
G. Duhamel, et al., Report by a French government and scientific delegation on the chikungunya epidemic, January 2006
"Chikungunya in La Reunion Island (France)," World Health Organization
, February 17, 2006
S. Higgs, et al, "Development and characterization of a double subgenomic chikungunya virus infectious clone to express heterologous genes in Aedes aegyptii mosquitoes," Insect Biochemistry and Molecular Biology
, October 2005
S. Higgs, et al, "Differential infectivities of o'nyong nyong and chikungunya virus isolates in anopheles gambiae and aedes aegyptii mosquitoes," American Journal of Tropical Medicine and Hygiene
, May 2005
JK Borchardt, "Two mosquito-borne diseases break past old geographic barriers," The Scientist
, November 21, 2000
J. Rusnak, et al., "Experience in the medical management of potential laboratory exposures to agents of bioterrorism on the basis of risk assessment at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID)," Journal of Occupational and Environmental Medicine
, August 2004.
R. Edelman, et al, "Phase II safety and immunogenicity study of live chikungunya virus vaccine TSI-GSD-218," American Journal of Tropical Medicine and Hygiene
, June 2000.