Dengue Virus Spreads North to Texas

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http://ens-news.com/ens/jun2003/2003-06-27-06.asp

 

Dengue Virus Spreads North to Texas

 

 

CHAPEL HILL, North Carolina, June 27, 2003 (ENS) - A new study from the

University of North Carolina describes the emergence and spread of a virulent

form of dengue virus from the Indian subcontinent to Latin America, including

Mexico.

Dengue (pronounced den-GAY) includes four distinct viruses, all transmitted via

the bite of Aedes mosquitoes, two of which, Aedes albopictus and Aedes aegypti,

are common in the southeastern United States.

The study, which appears online this week in the journal “Emerging Infectious

Diseases,” a publication of the U.S. Centers for Disease Control and Prevention,

used viral genetics to demonstrate the global movement of a virus associated

with severe disease.

Given that the major mosquito vectors of dengue are well established here, there

is concern that dengue viruses could be introduced into the United States and

transmitted to people, said Dr. Aravinda de Silva, assistant professor of

microbiology and immunology at University of North Carolina School of Medicine

and senior author of the study.

Dr. Aravinda de Silva is assistant professor of microbiology and immunology at

University of North Carolina School of Medicine (Photo courtesy )A handful of

cases have been documented in south Texas, close to the Mexican border, but may

not spread farther.

" I don't think dengue would ever become a serious problem in the United States

because humans are the main reservoir of this virus, " de Silva said.

The particular dengue virus subtype studied by de Silva and his team has been

responsible for epidemics of deadly dengue hemorrhagic fever in Sri Lanka, East

Africa and Latin America.

Dengue virus is characterized by internal hemorrhaging that sometimes leads to

shock - a drop in blood pressure and failure of blood cells to meet the

metabolic demands of the body

Dengue virus is a leading cause of death among children in Southeast Asia.

Mosquitoes become infected with dengue after biting a dengue infected person.

People infected with dengue virus develop dengue hemorrhagic fever or the less

serious dengue fever.

Dengue fever is also known as breakbone disease because of severe headache and

joint pain associated with it. In recent years hemorrhagic dengue has become

increasingly prevalent in tropical America.

Aedes aegypti mosquito on human skin (Photo courtesy Pagina Zero) " Historically,

illness associated with the dengue serotypes native to the Americas has been

very mild, and the virus that was responsible for hemorrhagic fever in this

region was a dengue serotype 2 strain introduced from Southeast Asia, " he said.

A serotype is a group of closely related microorganisms distinguished by a

characteristic set of antigens such as toxins or bacteria.

" It was, therefore, surprising to learn that the spontaneous outbreaks of dengue

hemorrhagic fever in Nicaragua and Panama in 1994 were caused by dengue serotype

3, " Dr. de Silva said.

Although dengue serotype 3 had been identified in the Americas more than 25

years ago, illness linked to it had been mild, he said.

" So those outbreaks associated with hemorrhagic fever meant one of two

possibilities - either the native virus had mutated to become more severe or

dengue serotype 3 from another part of the world had been introduced into Latin

America, " said de Silva.

The answer came from research that found the virus had moved across the globe to

Latin America. The new study describes the most likely route of spread and the

relationship to virus strains established in Asia and Africa.

" Our original intention had been to study how dengue hemorrhagic fever suddenly

emerged in South Asia in the late 1980s, " said Dr. William Messer, a doctoral

graduate of the university’s ecology department.

Hemorrhagic dengue fever has continued to be a public health problem in

Thailand, Indonesia and Malaysia since the 1950s, Messer said. All four dengue

serotypes have been documented there.

" It was puzzling that all four serotypes also circulated in South Asia, in Sri

Lanka and parts of India, yet dengue hemorrhagic fever was extremely rare, "

Messer said.

Then, abruptly, beginning in 1989, dengue hemorrhagic illness became common in

Sri Lanka.

The researchers then wanted to find out if the virus had changed. They isolated

dengue virus from pediatric patients in Sri Lanka. In those with hemorrhagic

disease, serotype 3 was prevalent. Patients with the milder disease, dengue

fever, showed infection with the other serotypes.

Patient with dengue hemorrhagic fever in Southeast Asia World Health

Organization (Photo courtesy ) " We then focused on serotype 3, collecting virus

isolates from Sri Lanka and other parts of the world, " de Silva said.

" Messer found that serotype 3 from Sri Lanka formed two genetically distinct

groups. In one group were viruses of serotype 3 that were related to dengue

disease prior to 1989, while the second group contained only viruses related to

disease after 1989. "

These findings provided the clue that a genetic change in the dengue serotype 3

virus circulating in Sri Lanka was responsible for the unexpected emergence of

severe disease, de Silva said.

The researchers then genetically sequenced dengue virus isolated from Latin

America and compared them to isolates from South Asia.

" We found that the group of Latin American isolates linked to severe disease

were more closely related to the same isolates associated with dengue

hemorrhagic fever in Sri Lanka, " Messer said. " And that virus has been isolated

all through Latin America and associated with dengue hemorrhagic fever from

Mexico down to Brazil. "

Unlike the West Nile virus, which is difficult to control because birds are the

main reservoir, human-mosquito exposure is a lot less here because so many

people live in air conditioned housing, de Silva said

“I doubt you can have the frequent, year round human-mosquito transmission

required for establishment of the virus that occurs in poorer countries.”

A report of the research can be found online at:

http://www.cdc.gov/ncidod/EID/vol9no7/03-0038.htm.

 

 

 

 

Copyright Environment News Service (ENS) 2003.

 

 

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