American public health authorities are bracing for the arrival of chikungunya in the continental United States. Houston, TX, is among the first cities where the mosquito borne illness is expected to appear. Dr. Kristy Murray spoke with the Examiner on March 25 about a surveillance study that Texas Children's Hospital and Baylor College of Medicine will be conducting from April 1 to Oct. 31.
For the next seven months, a child who present at the Texas Children's Hospital emergency department with a fever and has blood drawn will have additional testing performed on their specimen. Study researchers will test for the presence of antibodies to the West Nile virus, all four of the Dengue viruses and all the serotypes of the chikungunya virus. Murray said that the tests will show if the patient is currently fighting an infection by any of the viruses, or has had such an infection in the past.
Illnesses caused by the West Nile virus (WNV), the four Dengue viruses (DENV), and the chikungunya virus (CHIKV) are unrelated to each other. They share some similar symptoms but each illness has some distinct differences. Dr. Murray told us that public health efforts in the region are currently focused on the prevention of WNV illnesses.
Dr. Murray notes that 80 percent of those infected by the West Nile virus will have no symptoms. Less than one percent will have a severe illness, that can be fatal. Dengue and chikungunya may also produce infections without symptoms. Dengue can produce a hemorrhagic illness which may be fatal. Chikungunya illnesses are rarely fatal but can produce months of debilitating and disabling arthritic symptoms.
A study that Murray authored in 2010 found that there had been an outbreak of locally acquired dengue illnesses in 2003-2004 in the Houston area that had not been noticed. She also pointed to cases of locally acquired dengue along the Rio Grande in South Texas in 2013.
Chikungunya is new to the Western Hemisphere. It arrived in the islands of the eastern Caribbean in Dec. 2013, and is slowly spreading. Dr. Scott Weaver, a professor at the University of Texas Medical Branch at Galveston, expects that the first locally acquired chikungunya illnesses will be seen in the continental U.S in 12 to 24 months.
In Texas, West Nile virus is transmitted primarily through the bite of a female Culex quinquefasciatus mosquito. Humans are a secondary blood source for these mosquitoes who prefer to bite birds. The blood that is taken is used in the reproductive cycle of the insect. Dr. Murray says that Culex quinquefasciatus, called the southern house mosquito, is common throughout the state. Mosquito control efforts are primarily focused on eradicating this species.
Dengue and chikungunya are transmitted by two species of Aedes mosquito. Aedes aegypti is also called the Yellow Fever mosquito. Aedes albopictus, the Asian Tiger mosquito, is an invasive species that, Murray told us, was first discovered in the continental U.S., in the mid 1980s, in Houston. Both are vectors for transmitting any of the four dengue viruses from human to human. The Asian Tiger mosquito is a vector for a chikungunya serotype found in Asia and the Pacific while the Yellow Fever mosquito is the vector for the serotype spreading in the Caribbean, according to Dr. Weaver.
Both Aedes species are “aggressive day biters, Dr. Murray states. These mosquitoes also need blood to reproduce. She notes that Aedes aegypti is almost solely a human feeder while Aedes albopictus feeds on a number of hosts, including humans. Evidence suggests, she told us, that the Asian Tiger mosquito appears to be supplanting the Yellow Fever mosquito in its existing habitat.
Dr. Murray strongly believes that physicians, in and out of the Houston area, need to be educated about both dengue and chikungunya infections. The dengue outbreak a decade ago that was not detected at the time it happened is a striking argument for increased awareness on the part of the medical community. About 50 percent of the patients that Texas Children's sees in the emergency department are considered low income. Murray places those patients at greatest risk for mosquito borne illnesses, since their homes often do not have air conditioning or effective window and door screens.
The study should reveal any West Nile or dengue illnesses in the community. It will establish a baseline for pediatric illnesses that will be a useful measure of any future outbreaks. Dr. Murray says that the test will also show if chikungunya has reached the Houston area and perhaps gone unnoticed.
Kristy Murray, DVM, PhD, is the Associate Vice-Chair for Research and Associate Professor of Pediatrics in the Department of Pediatrics, Section of Pediatric Tropical Medicine, National School of Tropical Medicine, Baylor College of Medicine, Texas Children's Hospital Center for Vaccine Development and Director of the Laboratory for Vector-Borne and Zoonotic Diseases.