Preparing for Disease Outbreaks

News about the serious health risks posed by West Nile and Zika viruses generated much attention and concern in recent years, and continues to do so. “But depending on where people live in the U.S.A. or worldwide, their risks for contracting these or other types of serious mosquito-borne diseases will differ,” said Dr. Claudia Riegel.

As the director of the City of New Orleans Mosquito, Termite and Rodent Control Board, Riegel provides technical support for New Orleans and the pest control industry. And she is very much aware of the need for PMPs to correctly prepare for and efficiently respond to possible mosquito-borne disease outbreaks.

Riegel provided pertinent information on that subject to participants of the PCT Virtual Mosquito Conference.

REASONS FOR CONCERN. According to Riegel, there are valid reasons for concern when it comes to mosquito-borne diseases and their effects on the population.

“These diseases also include St. Louis encephalitis, Eastern equine encephalitis, chikungunya, malaria, dengue fever, Yellow fever and dog heartworm,” she said. “We worry about disease transmission by mosquitoes to humans and animals because of increased exposure due to damaged homes and (disaster) recovery efforts. Mosquitoes can interfere with response and recovery efforts of first responders, municipal and county workers and the general public.

“We’re concerned, as well, about lack of public awareness; conducive environments for increases in vector and pest populations; and for the potential to negatively impact the economy on tourism and travel. We’re concerned about possible lack of funding and support for control programs; and we’re aware of problems caused by inadequately trained workforces. Because you do rodent work doesn’t necessarily make you qualified immediately to do mosquito work.”

ROLES AND RESPONSIBILITIES. Those concerns, Riegel stated, give rise to the roles and responsibilities of the pest control industry.

“As a PMP, you have a responsibility to reduce the risk of disease, injury and human discomfort associated with vectors and pests,” she stated. “To do so you must correctly identify those vectors and pests and institute effective control activities. It’s important to determine and implement short- and long-term vector control and pest management strategies that may be used.”

Additionally, she said, you may have to provide guidance and information to partner agencies and the public, and provide educational resources to the public and related industries. “And you need to provide technical assistance and support for vector control and pest management issues and activities,” she said.

BASIC BIOLOGY. Riegel said it’s incredibly important to understand the basic biology of the various vectors and pests responsible for possible outbreaks.

“Mosquitoes have four life stages,” she said. “They include eggs, which can be laid on the surface or edge of water on containers or on soil above the water line; larvae, which live only in water; pupae, which also live only in water; and the adult.”

Understanding the basic biology of mosquitoes, she said, will aid in determining what control and strategies can be used for each situation.

According to Riegel, depending on the species, some eggs are laid singly on the surface or edge of water. Other mosquito species lay their eggs in groups known as “rafts” that float on the surface of water. The eggs of some species hatch after 24-36 hours, and the eggs of other species hatch after one, two or three years. There is an overwintering stage for the eggs of some species.

KNOW THE CLASSIFICATION. Riegel emphasized the importance of knowing the classification of various mosquito species. “These are based on larval habitat and include floodwater mosquitoes, permanent water mosquitoes and container mosquitoes.

“The floodwater mosquito classification can include several Aedes species, such as Aedes vexans and Aedes sollicitans. which can be very aggressive. They tend to bite humans and livestock and can have very large populations in spring and early summer. Look for them around wetlands, in woodland pools, roadside ditches and other low areas around creeks because these are great places for them to lay their eggs.”

According to Riegel, permanent water mosquitoes can include mosquitoes in the genera Anopheles, Culex and Mansonia. They can typically be found in quiet bodies of freshwater that are exposed to some sunlight with surface vegetation and very little wave action.

CULEX SPECIES.“You should know that several Culex species can vector the West Nile virus and the Eastern Equine Encephalitis virus that can result in serious and possibly fatal diseases. These mosquitoes are more active at night,” she said.

Container mosquito species, as the name implies, are those that develop in a variety of natural and artificial water-holding containers. “Examples of natural containers include tree holes and plants such as bromeliads. Artificial containers include a variety of man-made objects such as discarded tires, cans, flower pots, bird baths, pet dishes, etc. Important major species are Aedes aegypti, also called yellow fever mosquitoes; and Aedes albopictus, also called Asian tiger mosquitoes.”

Aedes aegypti is an introduced species that is typically more active during the daylight hours. They are found in urban and suburban environments in close association with people, she said. “They can be found in some warmer regions in the U.S. This mosquito is the principal vector for the Zika, yellow fever, dengue and chikungunya viruses.

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AEDES ALBOPICTUS. “Aedes albopictus was introduced in the U.S. in scrap tires. It is a significant pest and commonly found in containers in suburban and highly vegetated areas,” Riegel said. “It is also typically more active during daylight hours and is a competent vector for transmission of the yellow fever, dengue fever, chikungunya viruses and dog heartworm.”

Riegel pointed to important information resources available to PMPs. “These include the NPMA, local mosquito abatement districts, local universities and the USDA. Abatement districts can provide surveillance data, help identify mosquito species and assist in using traps, which are readily available,” she said.

Utilizing Integrated Mosquito Management (IMM) procedures is key to understanding and preparing to respond to the danger of possible outbreaks or emergencies, she asserted.

“IMM is really Integrated Pest Management zeroing in on mosquito control. It involves mosquito surveillance, source reduction, biological control, physical control and chemical control. It also involves resistance management, education and outreach,” she said.

SURVEILLANCE. In the surveillance phase of the mosquito control plan, it’s important to assess the high-risk areas in the area, and to determine the costs of equipment and labor. It’s also important to anticipate all of this before the mosquito season begins, Riegel says.

“Equipment should include traps, dippers, pipettes, flashlight aspirators, larval containers and bags for extra vials, pens, labeling tapes, etc.”

She discussed the importance of determining landing rates when doing surveillance. “This is used to measure adult mosquito activity in a specific area. It’s achieved by counting the number of mosquitoes that land on a person in a given amount of time — usually one minute. These counts are generally performed by the same inspector at each location for consistency.”

She cautioned, however, to not conduct landing rates if there is a risk of mosquito-borne disease transmission.

TRAPS. Riegel also mentioned several traps that can capture adult mosquitoes in the surveillance phase:

• The BG Sentinel Trap (Biogents, Regensburg, Germany) is a portable device used for the collection of the Aedes species in conjunction with lures and CO₂.
• The CDC Miniature Light Trap is a standard surveillance tool and was developed for the collection of mosquitoes and sand flies. A portable power source is needed.
• The CDC Gravid Trap was designed to catch gravid Culex females, which are attracted to the hay/fish oil infusion in a tub as an oviposition site. It too, will require a portable power source.

SUCCESSFUL OUTCOMES. For successful results, Riegel emphasized the need to start preparation activities early and to follow an IMM approach while conducting an evidence-based control program. “You’re going to need time to inventory and determine your needs and other related organizations to network with, and you’ve got to consider the possibility that additional resources may be required for additional workloads.”

She reminded PMPs that it’s important to stay up-to-date because new information about control techniques, equipment, and pesticides is constantly and readily available. “And it’s equally important to be transparent and make the effort to keep the public informed.”

The author has been writing about the pest management industry for more than 30 years.