The Student News Site of University of Arizona

The Daily Wildcat

80° Tucson, AZ

The Daily Wildcat

The Daily Wildcat


    Mosquitoes pose risk of new viruses in Arizona

    Briana Sanchez / Arizona Sonora News Service

    The Aedes aegypti mosquitoes are known carriers of Dengue fever and Chikungunya. These mosquitoes are larger and darker than the mosquitoes that transmit diseases like West Nile virus.

    Mosquitoes could carry new troubles to Arizona.

    Dengue fever and a second disease, Chikungunya, have started to crop up in areas surrounding Arizona, putting researchers on high alert about the looming threat the diseases could pose to the state.

    Both of these viruses are known as vector-borne diseases, carried and passed by mosquitoes. One particular type of mosquito, known as the Aedes aegypti, is a known carrier for both Dengue fever and Chikungunya, and Southern Arizona happens to be within this insect’s habitat.

    “These are fairly ornate mosquitoes, and they are fairly aggressive biters,” said Michael Riehle, an entomologist at the UA who researches the Aedes aegypti mosquitoes. “They have become a real pest species.”

    This breed of mosquito was common in Tucson and Southern Arizona until the 1970s, Riehle said, but then control measures with insecticides moved them out of Arizona. They were reintroduced in the 1990s into Tucson, possibly carried in along Interstate 10 from Texas in nursery plants, Riehle added. They’ve been in Southern Arizona ever since.

    Unlike the mosquitoes that normally spread West Nile, the Aedes aegypti primarily feed on humans. When they feed on a person already infected with Dengue or Chikungunya, the virus enters the mosquito’s body. After about a week to 10 days, the virus moves to the salivary glands in the bug, allowing it to move into the next person the mosquito bites, said Kacey Ernst, a UA entomologist who studies mosquito pathogens like Dengue.

    Out of all the people affected with Dengue, usually only about 30 percent of the people show any symptoms, which can range in severity. Those who show symptoms can experience an illness similar to the flu, with headaches, fever and joint pain, Ernst said. For more rare and serious cases, the infection can lead to Dengue hemorrhagic fever, where the patient can experience internal bleeding, as well as bleeding from the eyes and nose, Riehle said.

    While certain forms of the virus may be more serious, only about 2.5 percent of those infected with the more dangerous form of Dengue will die. If a person is going to show any symptoms of Dengue, they usually happen anywhere from three to five days to two weeks after the mosquito bite occurred.

    John Paul Jones III of Tucson knows exactly how the fever feels. He got Dengue in fall 2008, and, ironically, he researches how Arizonans apply mosquito control.

    “It was a fever that varied throughout the day, so there was a lot of sweating, and a lot of that was at night,” said Jones, a geography professor and dean of the UA College of Social and Behavioral Sciences. “Then, you’d wake up and kind of feel better, and you think it’s gone away, and then it gets worse as the afternoon progresses.”

    Jones went to his doctor, who tested him for mosquito-borne diseases after recognizing some of his symptoms and confirmed Jones had contracted Dengue fever.

    While most patients don’t even show symptoms of the disease, Dengue is a tricky virus for doctors and patients to deal with, as there are four different strains of the disease that can be passed by mosquitoes. While the body may build up immunity to one strain, if the patient gets a different strain of Dengue, the immune system will not recognize the virus, and the infection can become more serious due to immune complications.

    “It seems to be a misunderstanding with your immune system, so your antibodies say, ‘OK, we recognize this [strain] as sort of the one we’ve already developed an immunity to, but it’s not the real thing,’” Riehle said, “and that causes this whole immune complication.”

    While Dengue has been established in areas surrounding Arizona for the past few years, especially in Sonora, Mexico, and cities in Texas, Chikungunya has emerged as the newer and potentially more dangerous pathogen, as about 80 percent of those infected with the disease show symptoms, Ernst said.

    Like Dengue, those infected with Chikungunya will exhibit symptoms three to seven days after being bitten by an infected mosquito, where the most common symptoms are fever and joint pain. While the Chikungunya virus doesn’t lead to hemorrhagic fever like Dengue, the symptoms are often more severe, as the joint pain can last weeks, months or even years in extreme cases.

    However, because there aren’t different subtypes of Chikungunya like there is for Dengue, once a person has contracted the disease, they develop immunity to it, Ernst said, and people typically make a full recovery.

    Dengue has already appeared in the U.S. and in Mexico, as outbreaks have occurred in Key West, Florida, which, like Tucson, has large populations of the Aedes aegypti. Other outbreaks have occurred in the border region between Texas and Mexico, and a recent outbreak in San Luis Río Colorado, Sonora, showed health officials that the disease is moving across Mexico, landing itself less than 30 miles from the Arizona border.

    Chikungunya is a newer pathogen to reach the U.S., as it is normally found in Central and South America, like Dengue. So far, 14 different states have identified cases of the disease, with many cases occurring in Florida, according to the Centers for Disease Control and Prevention.

    There have been no officially reported cases so far of either disease originating in Arizona, though Jones, who spent the entire summer of 2008 in Tucson before traveling to London, said he believes he contracted Dengue in Arizona. No official records were shared with public health departments in the state to confirm the origin of his case.

    “We basically have a population of competent vectors that are able to transmit the virus,” Riehle said. “We have the virus circulating the just south of the border, and we have lots of movement across the border, so at some point, there is probably going to be an issue.”

    Until more cases of the diseases occur, different counties in Arizona have multiple ways to manage mosquito populations. Tucson uses the point source method, which is more oriented toward finding the water source where mosquitoes breed and hatch. Phoenix uses the blanket spray method, where it sprays everything so there is less concern with the water source, Jones said.

    “One of them is essentially ‘kill the babies’ and the other is ‘just kill the mosquitoes no matter where they are,’” Jones said.

    Since Aedes aegypti are floodwater mosquitoes, they breed in standing pools of water, allowing them to thrive in urban environments such as Tucson, where water in pet dishes, bird baths and rainwater collected at the bottom of pots makes for the perfect breeding ground, Riehle said. Because it takes the mosquitoes at least a week to grow from the larval stage to an adult mosquito, emptying out the containers every few days will usually kill the mosquito larvae. When dealing with the adults, using mosquito repellents normally keeps the insects at bay.

    While Dengue and Chikungunya haven’t officially crossed into Arizona, researchers and health departments have said that monitoring is key in order to stay ahead of the situation, especially with the established presence of Aedes aegypti in the state. Studying the factors that may have aided in the delay of the disease reaching Tucson is also key, Riehle said, as it could shed light on how and why the virus spreads in certain areas.

    “When West Nile was first racing through, there was a lot of money put into mosquito monitoring and testing the mosquitoes to see if they had the virus, … but the funding has pretty much dried up, and there’s not really a concern for these other viruses,” Riehle said. “I would argue that they are more of a concern than West Nile probably was, especially Dengue. If that gets established here, that is going to cause a lot of problems.”

    More to Discover
    Activate Search