Heartworms are an Expensive Side Effect of Mosquitoes in the Southeast

Elmer Gray, UGA Entomologist

County and city officials in the Southeast spend millions of dollars each year to combat mosquitoes. But those costs are only a fraction of what Southeastern families spend to keep their furry family members safe from mosquito-borne parasites.

MS Word clipartEach year Georgians spend between $9 million and $14 million treating heartworms in their dogs, said Elmer Gray, an Extension entomologist with University of Georgia Cooperative Extension. Dog owners across the country spend about $1.2 billion on heartworm prevention, and Gray estimates that about $40 million of that amount is spent in Georgia.

Those price tags dwarf the $7 million cities and counties in Georgia spend to keep mosquito populations under control and make heartworms the largest mosquito-related expense in the state.

“It really is the most expensive cost associated with mosquitoes,” Gray said.

Heartworm-related expenses are sometimes left out of studies calculating the economic impact of mosquitoes, but Gray believes these costs should be included.

“If it wasn’t for mosquitoes, there would be no dog heartworm problems,” Gray said. ”So consequently, the cost associated with heartworms – in my mind – is directly attributed to mosquitoes, thereby adding to the cost of dealing with this insect.”

He estimated the cost of prevention and treatment of heartworms with data provided by the UGA College of Veterinary Sciences and from Merial, a company that makes heartworm preventatives and other pharmaceuticals for animals.

The cost of preventative heartworm medicine is about $15 a month, and the cost of treating a heartworm infection can vary from between $600 and $1,000.

There are at least six species of mosquitoes that can transmit the heartworm parasite in Georgia. The flying insects pick up young heartworms, called microfilariae, when they feed on the blood of an infected animal. The microfilariae spend about two weeks maturing into larvae inside the mosquito, according to the American Heartworm Society.

When the mosquito takes its next meal, the larvae are deposited into the new host animal where they will mature into adult heartworms over the next six months.

Without treatment, the worms congregate around the right side of the heart and the arteries of the lungs where they can eventually cause heart or liver failure.

Dogs, cats and even humans can all be infected by heartworms, but the infections are most serious and most prevalent among dogs.

Southeastern states have the greatest prevalence of heartworm infections, and there’s an almost 100 percent chance that a dog living in Georgia will have the disease by age 5 if its owners don’t give it monthly preventive treatment, Gray said.

While cities and counties will continue to battle mosquito populations in Georgia, there is no way to reduce populations enough to prevent dogs and other animals from being infected with heartworms without medication.

“It would be impossible to prevent heartworm infections by controlling mosquito populations,” Gray said. “However, treating dogs with the proper preventative medicine is 100 percent effective at preventing the disease.”

Identifying and controlling different mosquito species

Rosmarie Kelly, Public Health Entomologist, Georgia Department of Public Health

The first step in controlling the mosquito species which are causing your client problems is to identify the local species.  Quite often, not all methods of control will work well for all species.   Knowing which species are the issue can help you determine future control methods.

So, how do you determine which species are active at any given time in your area?  The best method is to set out light traps in the area, collect the mosquitoes, and identify them.  If this is done in a systematic way, it is possible to develop a database of local mosquito species that will aid you in determining the best method of control at any given time.

Is this always feasible?  Unfortunately, no.  However, depending on where your client lives, some of this information may be available from other sources. Municipal mosquito control programs in Georgia rarely have sufficient funding to do mosquito surveillance.  However, there are a few programs that do collect surveillance data and may be willing to share information.

Mosquito information is available through the Georgia Mosquito Control Association. See http://www.gamosquito.org/resources/mosspecies.htm

Asian tiger mosquito, Susan Ellis, Bugwood
Asian tiger mosquito, Susan Ellis, Bugwood

The very least that should be done is to determine if the mosquito causing the problem is Aedes albopictus, the Asian tiger mosquito.   Asian tiger mosquitoes are small, aggressive, day-biting mosquitoes with black and white striped legs.

Since they do not fly far from their breeding ground, Asian tiger mosquitoes can be controlled through a combination of source reduction (eliminating breeding sites) and barrier spray (application of pesticide to vegetation where mosquitoes rest).  Not all mosquitoes will rest locally after biting, so barrier spray may not be as effective for all species but it works well for Asian tiger mosquitoes.

The most important reason to understand which mosquito species are causing problems at any given time is to assist with educating the client.  People tend to believe that all mosquitoes are the same, and often have unrealistic ideas about their control.  If you are well informed, it can help you when discussing control issues with the client and assist in keeping the client happy with your control program.

There are control situations that are better handled by commercial mosquito control companies. Having a list of local commercial applicators can be useful to a municipal program. 

Resources are available to assist with mosquito surveillance and identification.  Check out these sites:

http://www.mosquito.org/assets/Resources/PRTools/Resources/bmpsformosquitomanagement.pdf

http://www.mosquito.org/control

http://www.gamosquito.org

The Florida Medical Entomology Laboratory at the University of Florida offers an Advanced Mosquito Identification and Certification Course (http://mosquito.ifas.ufl.edu/Advanced_Mosquito_ID_Course.htm). 

The Georgia Department of Public Health has offered at least one mosquito ID course every year since 2002, and hopes to continue this tradition.  The various mosquito control products vendors not only offer equipment calibration, they also offer training opportunities.

Mosquito season continues through September

Elmer Gray, UGA Extension Entomologist

As we move into the last weeks of summer, be aware of the excellent conditions for mosquito development that this summer’s heavy rains have created. This year has been very different from recent years when we consider our local rainfall totals. To date, much of the state is 15 inches or more ahead of normal rainfall for this time of the year. As a result there is more standing water in our counties and communities than in recent memory. This standing water will provide excellent larval habitat for mosquitoes as we move into the last few weeks of summer.

Mosquitoes are semi-aquatic insects that require standing water for the larval and pupal stages. There are 63 species of mosquitoes

Mosquito life cycle
Mosquito life cycle, Art Cushman, USDA Systematics Entomology Laboratory, Bugwood.org

known in Georgia and as result they exhibit a range of life histories.

Typically, the female mosquito will lay eggs on the surface of the water, attached to the sides of a container just above the water’s surface or on moist soil that will become covered with water at a later date. After being covered with water and in due time, the eggs hatch and the larvae (or “wigglers” as they are commonly called) develop in the standing water. The larvae are filter feeders, feeding on small particles of plant and animal matter.

After developing through 4 instars the larvae progress to the pupal stage which is commonly called a “tumbler” due to their movement through the water. Both the larvae and pupae come to the water’s surface for air and move down into the water when disturbed. After 2-3 days in the pupal stage the adult mosquito that we are all familiar with will emerge onto the water’s surface.

In the late summer, this cycle can be completed in as little as 7 days. This summer, with the numerous cloudy days and relatively cool temperatures, this cycle has surely been extended. The cool night temperatures have probably been the only thing preventing even worse mosquito populations than we have already experienced.

Homeowners can often reduce mosquito populations around their homes and neighborhoods by being diligent. All standing water should be eliminated or treated with an EPA approved larvicide if mosquito larvae are present. Emptying buckets, plant saucers, boats, tarps and anything else that can hold water is extremely helpful. Keeping gutter’s clear of leaves and debris will help to eliminate the often neglected larval habitat of backed up gutters. Homeowners should also check those rain barrels that were so helpful in past year’s droughts. It is vital that screens are intact around all openings or these barrels will become highly productive mosquito habitats. In addition, screens on the windows and doors should be checked to make sure there are no holes. Many mosquitoes are attracted to light and will be drawn to open windows after dark when we’re trying to get some fresh air in our homes.

As of August 22, the Georgia Department of Public Health has only reported 2 human cases of West Nile virus (WNV) in Georgia. This low number of cases is in contrast to last year when Georgia experienced a record 117 cases of WNV with 6 deaths. The WNV is now known to occur across the state and has been isolated from mosquitoes in the four counties (Chatham, DeKalb, Glynn and Lowndes) where adult mosquito surveillance and testing are being conducted this year.

The low number of human WNV cases is likely related to the fact that the mosquito (the Southern House Mosquito) that transmits the disease often develops in the storm drain system, particularly during dry periods. With this year’s heavy and regular rainfall, the storm drain systems across the state are regularly flushed and populations of this mosquito have been somewhat suppressed. However, we don’t want people to let down their guard as football season arrives. The peak period for WNV transmission in Georgia has historically been August 15-September 15. The proper use of EPA approved repellents is highly recommended if people are expecting to encounter mosquito populations in the next few weeks.

Products containing DEET are recommended for use on children as young as two months by the American Academy of Pediatrics. Parents should apply the repellent to their hands and then apply it to the children. It is important to get good coverage and then wash the treated skin upon returning indoors.

In conclusion, mosquito control districts across the state are reporting high numbers of complaints due to a variety of species of mosquitoes that have benefited from the abundant rainfall. Health districts across south Georgia are also seeing an increase in Eastern Equine Encephalitis (EEE) in horses. This disease is caused by a virus that is transmitted by mosquitoes that typically develop in the swamps and woodlands below the fall line in Georgia. While cases are rare in humans, EEE symptoms range from mild flu-like illness to encephalitis (inflammation of the brain), coma and possibly death. Symptomatic cases have a fatality rate of 30-50% and it is classified as the most severe mosquito-borne disease of humans in the United States.

Preventing mosquito bites is crucial to avoiding any of the mosquito-borne diseases. Loose fitting, light colored clothing, coupled with the proper use of EPA labeled repellents, will go a long ways towards this goal by making us less attractive to mosquitoes.

 

For more information

Stinging and Biting Pests

Management of Pest Insects in and Around the Home

Georgia Mosquito Control Association