Tropical Diseases on the Rise in Texas
Public Health Feature — September 2014
Tex Med. 2014;110(9):41-44.
By Kara Nuzback
Hot, humid locations like Southeast Texas provide the perfect environment for the spread of viruses travelers typically bring back to the United States after a trip to the tropics.
Earl Matthew, MD, a Corpus Christi infectious disease specialist, says just as West Nile virus spread to New York in the early 2000s and then across the country, dengue and other diseases that travel via mosquito can make their way to the U.S. Gulf Coast.
"We have the potential for dengue to spread to the southern United States, no question," he said. "We're warming up some, and with warmth comes damp air and mosquitoes."
Mosquitoes transmit dengue, and the only way to prevent infection is to avoid mosquito bites. According to the Centers for Disease Control and Prevention (CDC), the virus infects up to 400 million people annually, and it is the leading cause of illness and death in the tropics and subtropics.
But the disease is also spreading in Texas. According to the Texas Department of State Health Services (DSHS), 23 Texas patients acquired dengue locally in 2013 — a fourfold increase from the prior 10 years combined. Dr. Matthew has practiced medicine in Texas for 40 years.
"I've been taught there's dengue in South Texas since I was a medical student," he said. "It's around."
Once-rare tropical diseases like dengue are becoming more commonplace in the state. DSHS officials identified the first case of chikungunya in Texas in July in a patient who traveled to the Caribbean and acquired the disease. DSHS urges physicians statewide to be on the lookout for warning signs, such as fever and body aches, especially in patients who have recently traveled to a tropical location. (See "Consider Chikungunya.")
Dr. Matthew says he has not seen any dengue cases in Corpus Christi, but many cases are asymptomatic. Physicians might never identify other cases because they would not think to test for dengue, he says.
"We could have it, but we wouldn't really know," he said. "Summertime severe flulike symptoms should be a sign, but they can occur with other systemic viral syndromes, like enteroviruses or early West Nile."
Dr. Matthew says Texas' severe drought is currently providing some protection for residents against disease-carrying mosquitoes. For more than three years, large portions of the state have operated under drought conditions.
"We haven't had rain in so long, we don't know what a mosquito looks like," he joked.
But, he says, an increase in rainfall will bring out more mosquitoes, and South Texas could wind up with a dengue outbreak, which could then spread to other areas of the state.
"Dengue is going to be the one we'll most likely have a problem with," he said.
Degree of Suspicion
Dr. Matthew says if a patient comes to you with a fever and terrible body aches, you should consider dengue, which is nicknamed "breakbone fever."
"It feels like all your bones are going to break," he said, adding the virus is not easy to identify or diagnose.
"It's not like strep throat, where we have a screening test. It's not as simple as that," he said. "There's so many other infections that present like it at onset, and it's not economically feasible to test for all of the possibilities."
The key to identifying the disease, Dr. Matthew says, is a healthy dose of suspicion. Also, determine whether the patient recently traveled to a tropical location or whether other cases of dengue have emerged in your practice area.
"You just have to think about it," he said. "You have to have a degree of suspicion that this is what you're dealing with."
If you suspect a patient has dengue or another tropical illness, he says, take a blood sample from the patient and perform an antibody test during the acute stage of the illness and another test two to three weeks later, when the antibodies have increased. (See "Identifying Dengue.")
If the patient's antibody levels for a specific disease are significantly higher in the second test, the physician can diagnose the illness and report it to DSHS, he says.
Texas law requires doctors to notify DSHS of suspected or confirmed cases of dengue within a week. Reporting forms are available online.
Unfortunately, tests can cost $200 to $300 each. If Dr. Matthew is unsure about the diagnosis during the acute stage of the illness, he says, "I'll draw blood and put it in the freezer."
In a few weeks, if he's still suspicious of dengue, he says he will then draw a second blood sample and send both to the lab.
"During the acute illness, you can have too many false positives," he said.
Be on the Lookout
Raquel Castillo, public health preparedness program director at the Cameron County Department of Health and Human Services, says health care professionals reported more than 50 cases of dengue in Cameron, Hidalgo, and Willacy counties combined in 2013. Twenty-three of those patients acquired the disease locally.
In comparison, only five patients acquired dengue locally in all three counties from 2003 to 2012, according to DSHS statistics. For more dengue statistics and information, visit the DSHS website.
Just before the 2013 outbreak, Ms. Castillo says, the department saw a number of cases of dengue emerge directly across the Mexican border.
"Then, we started seeing cases here," she said.
Ms. Castillo says the health department conducted an investigation of the outbreak. She and other officials, including the health inspector, went to the homes of patients with dengue and provided educational materials for the family on measures to take to avoid mosquito bites.
The health officials searched homes for standing water, including in buckets and potted plants outside the homes. According to DSHS, leaky pipes, outside faucets, air conditioner drain hoses, and animal water dishes are common breeding grounds for mosquitoes.
Ms. Castillo says the department has not heard of any cases of dengue so far this year, but the weather is still dry.
"Once the rain starts, that's when we start seeing the mosquitoes come out," she said. "We're on the lookout."
Peter Jay Hotez, MD, is founding dean of the National School of Tropical Medicine at Baylor College of Medicine and an endowed chair of tropical pediatrics at Texas Children's Hospital, both in Houston.
"There's a lot more dengue on the Gulf Coast than we currently realize," he said.
Dr. Hotez, his colleague Kristy Murray, PhD, and Tulane University School of Public Health and Tropical Medicine Professor Dean Pierre Buekens, MD, penned "The Gulf Coast: A New American Underbelly of Tropical Diseases and Poverty," published in the May issue of Public Library of Science Neglected Tropical Diseases.
The article cites two factors that promote tropical diseases in developing countries — extreme poverty and a tropical climate. Both are also prevalent in five states along the U.S. Gulf Coast, including the southeast area of Texas, according to the article.
The authors say a retrospective study led by Dr. Murray revealed Houston suffered from a seasonal outbreak of dengue fever in 2003. "No information beyond this period is available, so it remains a possibility that dengue emerged prior to 2003 and might still be causing seasonal epidemics," the article states.
The authors also address Texas' vulnerability to a chikungunya outbreak. Dr. Hotez says Dr. Murray planned to track chikungunya's progress throughout the summer.
"Every Friday morning at our tropical medicine clinic in the Harris Health System, we see patients with tropical diseases, many of which are acquired in Houston," Dr. Hotez said.
Chagas disease, a parasitic infection of the heart, and cysticercosis, a brain parasite, are common diagnoses, he says.
In partnership with the Sabin Vaccine Institute and the Texas Children's Hospital Center for Vaccine Development, the National School of Tropical Medicine at Baylor College of Medicine is working to develop vaccines for neglected tropical diseases, including illnesses affecting residents of Texas and the Gulf Coast.
The school offers an eight-week diploma in tropical medicine in the summer and winter for physicians to learn how to diagnose, manage, and treat tropical diseases.
"There's a lack of physician awareness of how to identify these diseases," Dr. Hotez said.
More information about educational opportunities at the school is available online.
Kara Nuzback can be reached by telephone at (800) 880-1300, ext. 1393, or (512) 370-1393; by fax at (512) 370-1629; or by email.
Dengue is not the only tropical disease to emerge in the United States. Chikungunya, a virus also transmitted by mosquitoes, has spread rapidly across the globe in the past decade.
In December 2013, the Caribbean saw its first local transmission of chikungunya. The Pan American Health Organization reports more than 5,000 confirmed cases and more than 180,000 suspected cases of chikungunya in the Caribbean as of June 20.
More recently, chikungunya has popped up in the United States. Texas health officials identified the first case of chikungunya in July in a patient who acquired the disease in the Caribbean. The Georgia Department of Public Health reported its first case in June in a patient who had also traveled to the Caribbean.
As of June, the Tennessee Department of Health had confirmed two cases of chikungunya, and the North Carolina Department of Health and Human Services had confirmed one.
All the U.S. patients with chikungunya acquired the disease in the Caribbean, but the mosquitoes that transmit the virus are of the Aedes species, which can also transmit dengue and which live in parts of the United States, including Texas.
The TMA Committee on Infectious Diseases encourages you to consider chikungunya virus infection in patients who have traveled to areas with known outbreaks, such as the Caribbean, and who present with common symptoms such as acute fever and severe joint pain.
Peter Jay Hotez, MD, founding dean of the National School of Tropical Medicine at Baylor College of Medicine, says to spot dengue, physicians should look for patients with a fever, rash, headaches, and problems clotting blood. Newer laboratory tests can help physicians identify the disease quickly, he says.
Though no vaccine exists for dengue or chikungunya, death is rare, according to the Texas Department of State Health Services. In most cases, patients need only to treat the symptoms by resting, drinking fluids, and taking aspirin-free fever medications. But patients who develop dengue shock syndrome, Dr. Hotez says, need intensive care.
He says normally a patient with dengue will experience about a weeklong incubation period, followed by a fever, chills, and eye pain. The patient may develop a skin rash toward the end of the symptomatic portion of the disease. By day five, the fever starts to go down.
The Centers for Disease Control and Prevention reports the condition can worsen and become dengue hemorrhagic fever (DHF), which causes the patient to bruise easily and spit up blood; the condition can be fatal.
Dr. Hotez says DHF occurs frequently in patients with more than two types of dengue; four types exist. He says warning signs of severe dengue include abdominal pain or tenderness, persistent vomiting, bleeding from the gums or other mucosal bleeding, liver enlargement, and a rapid decrease in platelet count.
He says doctors should always manage dengue or other tropical diseases in consultation with an infectious disease physician or contact the National School of Tropical Medicine at (713) 798-1000.