Running out of Room

Tick-borne diseases are the most common vector-borne illnesses in the United States. Now that spring is here and tick activity is increasing each day, a quick update and refresher on ticks of public health importance is timely for pest management professionals.

The Centers for Disease Control and Prevention (CDC) reports that Lyme disease, Rocky Mountain spotted fever (RMSF) and ehrlichioses afflicted more than 22,000 Americans in 2004. Human cases of regionally acquired tick-borne diseases not reported to CDC, such as Southern Tick-associated rash illness (STARI), Colorado tick fever, tick paralysis, babesiosis and tick borne relapsing fever (TBRF), occur each year as well. As a result, the public health message to consumers is clear: Keep your family away from ticks.

As humans incorporate rural land into urban centers and locate suburban developments in natural habits, the prevalence of tick-borne illnesses will continue to increase. These changing land-use patterns create the perfect environment for a tick population explosion, right in the middle of suburbia. Pest control technicians are faced with eradicating these public health pests from yards and homes, even though many state regulations limit the scope of structural pest control applications to within 25 feet of a building.

Tick control is a challenging service that begins with the proper identification of the tick species infesting the property. Every species of tick has a unique lifecycle that requires a specialized control plan. Soft tick species (Ornithodoros sp.), vectors of tick-borne relapsing fevers around the world, are found indoors coming from rodent or bird nests. Brown dog ticks are the only hard tick species that can complete their entire life cycle indoors and recent evidence shows they are capable of vectoring RMSF. Other hard tick species are unable to complete their lifecycle indoors, instead hitching a ride inside a building on pets or clothing. It is important that pest control technicians fully understand the biology of local tick species and the types of diseases they vector in order to direct control activities. The following examples illustrate this point.

PCOs’ KNOWLEDGE OF TBRF. Since 1970, more than 300 people have acquired tick borne relapsing fever from the bite of a soft tick in California. The disease is reported from states west of the Mississippi river, mostly at high elevations (more than 4,000 feet).

Soft ticks live in the nests of rodents and birds. But ticks will search out an alternate host if these animals leave their nests. Soft ticks primarily feed at night, while a person is sleeping. The entire feeding process can be completed in as little as 20 minutes, after which the tick crawls to a near by crack or crevice to lay eggs, unable to move long distances because of their increased body size. Soft ticks can vector Borrelia sp. bacteria to humans that were previously acquired from feeding on a bird or rodent as a larvae or a nymph. Tick-borne relapsing fever is rarely fatal, but can require hospitalization. Symptoms of TBRF include a high fever, headache, chills and muscle aches with febrile (fever) episodes lasting one to seven days, separated by one to 10 afebrile days, until the febrile episode returns, sometimes relapsing up to 10 times.

The California Department of Health Services, Vector Borne Disease Section recommends that persons who became ill from tick borne relapsing fever contact a local pest control professional to remove rodent and bird nests from the structure where they believe they were bitten, treating cracks and crevices with a residual acaracide around the rodent nest and in rooms used for sleeping.

However, multiple TBRF cases over the last 20 years have been associated with a given site suggesting that control activities provided by pest control technicians may not be efficacious. In 2006, CDHS initiated a phone survey of pest control operators providing services in counties found to have the highest prevalence of TBRF cases.

Forty-two pest control companies were contacted via phone and asked to participate in a short survey about TBRF and soft tick control practices. Only 12 companies participated in the survey, the other 30 declining for “unspecified reasons.” One company reported it had provided service for soft ticks in response to TBRF. CDHS sent each company a “Tick Borne Relapsing Fever” brochure with information on soft tick ecology, as well as the handout “Tips for pest control operators working in counties endemic for TBRF.”

Per CDC recommendations, when conducting rodent control in buildings where soft ticks are likely to occur, it is important to locate and remove rodent nests and the ticks they contain from walls, ceilings and floors. To prevent reinfestation, identifying and sealing points of rodent entry into buildings is critical.

BROWN DOG TICKS & RMSF? Rocky Mountain spotted fever is caused by a rickettsia bacterium that is transmitted primarily by the American dog tick (Dermacentor variabilis) and the Rocky Mountain wood tick (Dermancentor andersoni).

Recent disease investigations show that the brown dog tick could be a potential vector of RMSF to humans. In 2004, two brown dog ticks were removed from a 10 year old in Arizona who was confirmed as having RMSF. Brown dog ticks also were found on the pet dog and collected from the home of the child. Those ticks later tested positive for Rickettsia rickettsii, which causes RMSF. Larvae, nymph and adult brown dog ticks primarily feed on dogs, however, they will feed on other mammals when they are present.

Brown dog ticks are the only tick in the United States that is able to complete their entire lifecycle inside a building. It is the most widely distributed tick in the United States, with a great reproductive potential. A single female tick can lay up to 5,000 eggs in her lifetime. Homes and yards can become heavily infested with this species, presenting a challenge to pest control professionals striving for eradication. A combination of veterinary care for the infested dog and structural pest control is needed to reduce populations in a yard.

When customers complain of a tick infestation, it is important to identify the tick species present to direct control activities. If an American dog tick infestation is found in the yard, treatments to the interior of the house may not be necessary. However, properties infested with brown dog ticks may also experience high tick populations living indoors. The CDC, as well as many state health departments, provides tick identification cards free of charge that can be helpful to pest control professionals identifying infestations in the field.

AN ALTERNATIVE? The Maxforce Tick Management System from Bayer Environmental Science was withdrawn from the market in early 2006. Many pest management companies used the Maxforce Tick Management System in customers’ yards at the interface between landscaping and the woods. Waltham Services, providing pest management services on the East Coast, field tested the program with Bayer Environmental Science. Douglas Smith, operations manager with Waltham Services, notes that without the Maxforce Tick Management System, the timing of tick control services in the spring and fall is paramount to reduce tick populations and combat the risk of disease transmission.

The single greatest challenge to controlling black legged ticks in a customer’s yard is the inability to treat all neighboring properties with the same integrated pest management approach. Customers are advised to trim or eliminate dense weed growth and vegetation in the yard, especially at the edges of manicured lawns, to minimize ground cover attractive to ticks and tick hosts. Ticks do not preferentially live on lawns, but as mice, birds, deer and pets cross forested and overgrown areas onto lawns — attracted to bird feeders, gardens and homes — ticks are brought along. A human’s risk of acquiring Lyme disease is related to the density of ticks in an area where they could be exposed.

Effectively targeting reservoir hosts with limited pesticide application is the gold standard for tick control and PCOs across the United States are looking forward to the next alternative to traditional tick control services.

The author is an associate public health biologist with the Vector-Borne Disease Section of the California Department of Health Services. She can be reached at lkrueger@giemedia.com.

References

All disease data taken from Summary of Notifiable Diseases — United States 2004 in the MMRW.

Soft tick control recommendations from CDC: Centers for Disease Control and Prevention. Hantavirus pulmonary syndrome — United States: Updated recommendations for risk reduction. MMWR 2002; 51 (No. RR-9).