[Mosquito Suppliment] Mosquitoes pose old and new health threats, Goddard says

One of the highlights of the recent M.I.S.T Conferences was keynote speeches from Dr. Jerome Goddard, associate extension professor of medical and veterinary entomology, Department of Entomology and Plant Pathology, Mississippi State University. Goddard provided an overview of vector-borne diseases and shared his perspective on pest management professionals’ role in mosquito control, including the use of pesticides as part of an integrated mosquito management program.

Pest management professionals should be proud of the role they play in protecting public health, Goddard said. "If you are doing pest control of any type you’re helping to manage, prevent or control (vector-borne diseases). So, you do have a role in protecting public health. Don’t be ashamed of what you do. Be proud of what you do."

Could that role be expanding? It could be, according to Goddard. Here’s why: Most of the vectors that carry diseases are located in tropical areas. If, in fact, the Earth’s temperature is rising slightly, as some scientists suggest, it stands to reason that these vectors will spread northward. "I don’t know what I think about global warming," Goddard said. "It does seem like we are in a warming trend, but nobody knows for sure the causes of it. But, it is important to think about because if there is global warming those tropical bug diseases could move north."

Even if that scenario does not play out, other public health issues related to pests are prevalent in the United States. For example, humans can suffer direct effects from bites/stings and other exposure. These include myiasis (fly larvae in human tissues), as well as blisters and discoloration from beetles, millipedes, and other arthropods. Humans also can suffer indirect effects such as biological or mechanical disease transmission.

• Biological transmission – When biological vectors harbor pathogens within their bodies and deliver pathogens to new hosts in an active manner, usually a bite. Examples include malaria, dengue, yellow fever, West Nile virus.
• Mechanical transmission – When mechani-cal vectors (e.g., flies, rodents, cockroaches) transmit disease agents or contaminate products simply by physically transmitting germs on their body parts.

In the U.S., West Nile virus (WNV) is the mosquito-borne disease that grabs most of the headlines. An interesting observation from Goddard was that WNV seems to be cyclical. For example, Goddard noted that in Mississippi there were 193 cases of WNV in 2002. That number dropped to 83 cases in 2003, then to 52 cases in 2004; WNV cases then rose to 70 cases in 2005, 184 cases in 2006 and 117 cases in 2007. Goddard said he thinks what happens is that large numbers of birds will build up an immunity to WNV (during down cycles), then after these birds die off, they are replaced by a "new batch of birds" that are more susceptible to WNV.

What could be the "next West Nile virus" in the U.S.? Goddard thinks it might be the Chikungunya virus, which is transmitted to humans by Aedes mosquitoes (perhaps the most common mosquito in the U.S.). "The reason we don’t have this disease is because we don’t have the virus," Goddard said. "How can the virus get here? Maybe an infected animal, or person or mosquito gets brought here. That’s how West Nile got here."

According to the Centers for Disease Control (CDC), the Chikungunya virus was first isolated from the blood of a febrile patient in Tanzania in 1953. The disease has shown an ability to spread quickly. Goddard said that hundreds of thousands of cases were reported in Indian Ocean Islands in 2006 (250,000 cases were confirmed on one island alone). It was recently reported in Italy, which is significant because it marks the virus’s appearance in a Westernized country. Unlike West Nile virus, Chikungunya is unlikely to result in encephalitis. Symptoms of this disease include: sudden onset of fever, severe chills, painful joints, low white blood cell count, etc.

The author is Internet editor and managing editor of PCT magazine.
 

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Research sheds light on
how mosquitoes find a host

The potentially deadly Yellow Fever-transmitting Aedes aegypti mosquito detects the specific chemical structure of a compound called octenol as one way to find a mammalian host for a blood meal, Agricultural Research Service (ARS) scientists report.

Scientists have long known that mosquitoes can detect octenol, but this most recent finding by ARS entomologists Joseph Dickens and Jonathan Bohbot explains in greater detail how Ae. Aegypti — and possibly other mosquito species — make this detection.

Dickens and Bohbot, at the ARS Invasive Insect Biocontrol and Behavior Laboratory in Beltsville, Md., have shown that Ae. aegypti taps into the "right-handed" and "left-handed" structural nature of octenol, which is emitted by people, cattle and other mammals. This ability to detect the "handedness" of molecules has been shown in mammals, but the discovery is the first case of scientists finding out how it works in an insect, according to the researchers.

When they hunt for a blood meal, mosquitoes hone in on a variety of chemicals, including carbon dioxide, lactic acid, ammonia and octenol. Octenol is one of many carbon-based compounds that have a molecular structure that can take on either a "right-handed" or "left-handed" form. Each form is a mirror image of the other, and a form's "handedness" is determined by how its molecular bonds are assembled.

The scientists used frog eggs to help them make their discovery. They injected RNA from Ae. aegypti into the frog eggs, allowing the egg membranes to mimic the mosquito’s ability to detect octenol. Then the scientists attached microelectrodes to the frog egg cell membranes, passed octenol over them and recorded the electrical signals stimulated by the odors.

They ran the tests using both the right- and left-handed forms of octenol. The scientists found heightened electrical activity when the membrane was exposed to the right-handed form, and weakened activity when it was exposed to the left-handed form.

There are many natural compounds that can take on either a right-handed or left-handed form. While the effects of those differences on many plants and animals remains a mystery, the report, published in PLoS ONE, shows the effects of octenol’s dual structure on the Yellow Fever mosquito and adds to scientists’ understanding of how mosquitoes sense the world around them. It also may open the door to speedier development of better mosquito repellents and traps, according to Dickens.