Bug off! UA scientist explains mosquito penchant for human blood

Nicholas Valenzuela Arizona Daily Wildcat John Hildebrand accepts a plaque for speaking about "The Most Dangerous Animal in the World" yesterday as part of the Building Academic Community Speaker Series in Gallagher Theatre. Hildebrand said that mosquitoes are the most dangerous animal since they carry malaria parasites that kill 200-300 million people a year.

"For us Americans particularly, they are a pest," said John Hildebrand, a UA neurobiology regents professor, to about 50 listeners in Gallagher Theatre. "But for other places in the world that have mosquito-born diseases, it's more than a matter of being a pest. It's a matter of life and death."

Hildebrand spoke about potential risk of mosquitoes in a speech titled "The Most Dangerous Animal in the World" as part of the weekly Building Academic Community speaker series.

Most people are familiar with the itching sensation associated with a mosquito's bite but don't know of the more dangerous side-effects that can result in death, he said.

Mosquitoes spread malaria parasites that kill 200-300 million people a year, Hildebrand said. Those mosquitoes are limited to one species, the anopheles gambiae.

Malaria affects 300-500 million people at any given moment, he said.

Although malaria victims are concentrated more heavily in Africa, India and South America, more than 1,000 United States citizens die each year of the disease, he said.

Mosquitoes used to feed off of plants but evolved into blood suckers, Hildebrand said. The insects found that the blood from animals with open wounds offers a protein-rich diet.

"It provided a food source, especially to females that were producing eggs," Hildebrand said.

Malaria parasites are ingested by mosquitoes after sucking the blood of an infected person or animal.

The parasites then travel through the mosquito's digestive tract, penetrating the gut wall, and are secreted through the saliva glands. They are transmitted when the mosquito bites another person, replacing the blood with the mosquito's saliva.

"These parasites live on hemoglobin in the blood cells," Hildebrand said.

Researchers have studied the biting habits of the mosquito.

As an example, Hildebrand said a graduate student in Switzerland volunteered to sit in a mosquito-infested room to observe where different species of mosquitoes tend to bite the most. The student received more than 100 bites per sitting, he said.

Results show that the anopheles gambiae has a foot fetish.

Attempting to find the reason behind their inclination for the foot, Hildebrand said, researchers washed a volunteer subject's feet with unscented soap so no fragrances would interrupt the experiment. That time, no area was bitten more than another.

The researchers found that feet emit an aroma similar to the smell of Limburger cheese. When a brick of the cheese was placed in the room with the mosquitoes, they attacked it in the same way they did human feet.

Researchers have studied measures to prevent mosquitoes' attraction to humans.

"The most effective way ultimately to control the spread of infectious diseases like this is to interrupt the relationship between the vector - the mosquito - and the host - the skin of the human being," Hildebrand said.

Researchers have since developed an insect repellent commonly known as deet.

"It's the most effective insect repellent that's ever been discovered," Hildebrand said.

Deet can be toxic to humans and is potent for several hours after application.

Another method to repel the anopheles gambiae is gene therapy - changing the insect's genetic makeup to curb its appetite for humans, he said.

Although those mosquitoes do not live in the U.S., they may start migrating north from Mexico in the next three years, Hildebrand said.

Stephanie Corns can be reached via e-mail at Stephanie.Corns@wildcat.arizona.edu.