Dengue and Chikungunya: Mosquito-Borne Invaders

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Dr. David J. Holcombe
Dr. David J. Holcombe

Dengue and Chikungunya are two viral diseases that are poised on our borders.  Cases are regularly brought back by travelers, notably from the Caribbean.  Both diseases are transmitted by infected Aedes mosquitoes, which are present throughout the Southern United States, including Louisiana.

 

Dengue is found in the Caribbean, as well as in South American, Africa and Southeast Asia.  Travelers to Caribbean islands can and do become infected and bring the disease back to the U.S.  Dengue has been reported in indigenous (non-imported) cases in Key West, Florida and on the Texas-Mexican border.

 

The mosquito acquires Dengue by biting an infected human and, after an incubation period of a few days, transmits the organism in its saliva when it bites another person.  Once infected, there is an incubation period of about a week in humans.  After that, around 25% of cases develop symptoms, with fever, severe joint and muscle pains, a diffuse rash, and spots related to platelet dysfunction (purpura).

 

This “febrile phase” (fever phase) is followed by a “critical phase” in around 5% of symptomatic individuals.  Symptoms include abdominal pain and vomiting and may lead to hypotension and shock due to fluid shifts from the vessels to the tissues.  There can be blood in the stool, pancreatitis, hepatitis and even death.  Prompt recognition of this “critical phase” and aggressive fluid administration reduces mortality from 10% to only 1%.

 

When Dengue is suspected, it can be confirmed with certain specialized lab tests (PT-PCR or DENV Non-structural protein). There are no specific treatments for Dengue.  Aspirin containing products should be avoided since they can worsen bleeding.

 

Chikungunya, another viral disease transmitted by the same mosquitoes, is found in Africa, Southeast Asia and also, more recently, in some Caribbean islands.  Like Dengue, it can cause fever, joint pain and a rash, making it difficult to differentiate from Dengue in patients from susceptible areas (notably the Caribbean).  Like Dengue, it can be confirmed by specialized lab tests (IgM) and has no specific viral treatment.  The first case of a locally acquired infection has just been reported in Florida.

 

Prevention remains the best option, with careful avoidance of mosquitoes and effective mosquito control efforts.  Unfortunately, both of these diseases could establish themselves in the Southern United States.  Aedes aegypti, one of the mosquitoes that transmit both viruses, has proven both persistent and adaptable in urban environments.  Its presence, along with that of these two viral diseases, remains a constant threat.

 

The importation and dissemination of West Nile Virus, another mosquito-borne viral disease, serves as a constant warning that such diseases are only waiting for their opportunity to invade the United States.  Fortunately, neither Dengue nor Chikungunya seems to infect birds, making rapid, widespread dissemination more unlikely than with West Nile Virus.   For more information, consult www.cdc.gov.