Mosquitoes threaten Arizona with new diseases

Dr. Riehle studies mosquitoes in his lab that are found in Ariz. that can spread two diseases that are popping up in boarding states. Dengue, one of the diseases, is a viral disease that some of the mosquitos are infected with. The mosquitos go from egg to larvi, to pupi, to full grown mosquito while in the lab. Photo by Briana Sanchez/ Arizona Sonora News Service
Dr. Michael Riehle studies mosquitoes in his lab that are found in Ariz. that can spread two diseases that are popping up in boarding states. Dengue, one of the diseases, is a viral disease that some of the mosquitos are infected with. The mosquitos go from egg to larvi, to pupi, to full grown mosquito while in the lab.
Photo by Briana Sanchez/ Arizona Sonora News Service

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,” says Michael Riehle, an entomologist at the University of Arizona 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 says, but then control measures with insecticides moved them out of Arizona. They were reintroduced in the 1990s into Tucson, possibly carried in along I-10 from Texas in nursery plants, says Riehle. 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, says Kacey Ernst, an entomologist at the University of Arizona who studies mosquito pathogens like Dengue.

Out of all the people affected with Dengue (pronounced DENG-gee), 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, said Ernst. 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, says Riehle. 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 3-5 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, who is a geography professor and dean of the College of Social and Behavioral Sciences at the University of Arizona. “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,’ and that causes this whole immune complication,” says Riehle.

Photo by Briana Sanchez/ Arizona Sonora News Service
Dr. Riehle studies the Aedes Aegypti mosquito in his lab, where he follows the growth cycle of the mosquito from the larval stage to an adult. Photo by Briana Sanchez/ Arizona Sonora News Service

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

Like Dengue, those infected with Chikungunya will exhibit symptoms 3-7 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 and people typically make a full recovery, says Ernst.

Dengue has already appeared in the US 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, 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, 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,” says Riehle. “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 towards finding the water source where mosquitoes breed and hatch. Phoenix uses the blanket spray method, where they spray everything so there is less concern with the water source, says Jones.

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

Since the Aedes Aegypti are floodwater mosquitoes, they breed in standing pools of water, allowing them to thrive in urban environments like Tucson, where water in pet dishes, bird baths, and rainwater collected at the bottom of pots makes for the perfect breeding ground for the mosquitoes, says Riehle. 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 repellants normally keep the insects at bay.

While Dengue and Chikungunya haven’t officially crossed into Arizona, researchers and health departments say 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 says, 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,” says Riehle. “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.”

Dr. Riehle's Lab
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. Photo by Briana Sanchez / Arizona Sonora News Service

Michaela Kane is a reporter for Arizona Sonora News, a service from the School of Journalism with the University of Arizona. Contact her at mlkane@email.arizona.edu.

Click here for high-resolution photos.

Leave a Reply

Your email address will not be published.