[Focus On Public Health] Enemy At The Gate

In the 1960s, health officials predicted infectious diseases – particularly those transmitted by insects – would soon be a thing of the past. That prediction could not have been further from the truth.

Today, there seems to be an endless stream of new and "emerging" insect-, tick- and rodent-transmitted diseases that impact the U.S. Several of those diseases have a direct impact on the pest management industry, either because they present an occupational risk or they provide an opportunity for additional service to the consumer.

For the pest management professional who wants to start a vector control service, it is important to recognize that significant resources are required. The focus of most vector control programs – and particularly mosquito control – shifts from the individual premises to the community or even an entire county. Surveillance – daily or weekly monitoring of vector species abundance – is a major part of these programs. These shifts will require major staffing changes.

Some issues of training, licensing, and legal liability are briefly outlined here. It is important to remember that these issues can vary from state to state, and it is a PCO’s responsibility to ensure that he or she is in compliance with all applicable regulations.

DISEASES & CONDITIONS OF CONCERN. Mosquito-transmitted diseases. Arboviral encephalitis is a term that describes an infection of the brain by an arbovirus (short for arthropod-born virus). There are four long-established mosquito-transmitted diseases that occur in the U.S.: eastern (EEE) and western (WEE) equine encephalomyelitis, LaCrosse (LAC) and St. Louis (SLE) encephalitis. In 1999, a fifth arbovirus, West Nile virus (WNV) appeared in New York City and has since spread throughout most of the United States. All of the arboviral encephalitis viruses exist as natural cycles (or zoonoses) involving mosquitoes (usually in the Culex or Aedes) and birds (EEE, SLE, WEE, WNV) or small mammals. Isolated cases of dengue and malaria have also been reported in the U.S. — usually from travelers returning from areas where those diseases are widespread.

Tick-transmitted diseases. Lyme disease (and possibly one or more related infections) constitutes the most commonly reported arthropod transmitted disease in the U.S. Classical Lyme disease, caused by the sphirochete Borrelia burgdorferi, is transmitted by the blacklegged (deer) tick, Ixodes scapularis, in the eastern and midwestern states, and by the western blacklegged tick, Ixodes pacificus, in the western states. Lyme-like infections have been reported from areas where these tick vectors are absent. It is possible that additional Borrelia species, transmitted by other tick species, also occur in the United States.

Rocky Mountain spotted fever (RMSF) is the most severe and most frequently reported rickettsial illness in the United States. The disease is caused by Rickettsia rickettsii, a species of bacteria that is spread to humans by ixoid (hard) ticks. The name Rocky Mountain spotted fever is somewhat of a misnomer. It is now recognized that this disease is broadly distributed throughout the continental United States, as well as southern Canada, Central America, Mexico and parts of South America. Some specialists have proposed renaming the disease American tick typhus. Rocky Mountain spotted fever remains a serious and potentially life-threatening infectious disease despite the availability of effective treatment (tetracycline and chloramphenicol) and advances in medical care. About 3 to 5 percent of individuals who become ill with the disease still die from the infection.

Ticks are the natural hosts, serving as both the reservoirs and vectors of R. rickettsii. They transmit the organism to vertebrates primarily by their bite. Less commonly, infections may occur following exposure to crushed tick tissues, fluids or tick feces. There are two major vectors of R. rickettsii in the United States, the American dog tick, Amblyomma americanum and the Rocky Mountain wood tick, Dermacentor andersoni.

Non-arthropod-transmitted diseases. Hantavirus pulmonary syndrome (HPS) is caused by one of several viruses that infect rodents. Although primarily associated with the southwestern U.S., HPS cases have been documented in the U.S., Canada and Latin America. Aerosols are the major route of transmission from rodents to humans. Humans, who are dead-end hosts, may contract the virus when saliva or excreta from infected rodents are inhaled as aerosols produced directly from the animal. Transmission may also occur when fresh or dried materials contaminated by rodent excreta are disturbed, directly introduced into broken skin, introduced into the eyes or possibly ingested in contaminated food or water.

Fungal infestations have recently received major attention in the media, particularly "black mold" Stachybotrys chartarum (also known as Stachybotrys atra). Molds are common in buildings and homes and will grow anywhere indoors where there is moisture. The most common indoor molds are Cladosporium, Penicillium, Aspergillus and Alternaria.

While it is less common than other mold species, it is not rare. The greenish-black mold grows on material with a high cellulose and low nitrogen content, such as fiberboard, gypsum board, paper, dust and lint. Growth occurs when there is moisture from water damage, excessive humidity, water leaks, condensation, water infiltration or flooding. For extensive amounts of mold it is advisable to contact a professional who has experience in cleaning mold in build- ings and homes. In all cases, prevention is paramount. As part of routine building maintenance, buildings should be inspected for evidence of water damage and visible mold. The conditions causing mold should be corrected to prevent mold from growing.  

PCOs’ ROLE. Disease vector control and, to a lesser extent, rodent control, have most often been publicly funded activities (e.g., through special taxing districts or the local health department).
In some parts of the U.S., however, commercial pest management companies have begun to enter the vector- and rodent-borne disease prevention business.
For those contemplating becoming involved in this line of work, there are several important considerations. Most of these diseases are zoonoses — found in nature. Prevention and control involves much more than just the home and immediate premises.

Since some mosquitoes can fly many miles in a single night, local residents may see a small area mosquito control program as ineffective (because mosquitoes are flying from outside the zone of control). Ongoing surveillance, often for both the vector and pathogen, is an integral part of disease prevention and control. These activities can severely tax the resources of a small pest management company.

In vector control, the most important prevention activities are habitat reduction (draining or treating water-holding containers, landscaping, drainage, etc.) and prevention of access (properly maintained window and door screens, rodent-proofing, etc.). In general, as noted previously, pesticide applications must cover large areas (e.g., an entire county) to be truly effective. Some states require separate public health pesticide applicator licensing – know local laws.

Personal Protection Issues. Pest management professionals tend to have higher occupational exposure to many of these diseases. Thus, personal protection is essential. Depending on the location and the type of pest control being performed, protective measures may include repellents, protective clothing, a respirator or other precautions. In dealing with the public, the pest management professional is an educator. There are always opportunities to educate the public in the appropriate use or application of prevention. Some obvious examples include elimination of rodent harborage, mosquito larval habitats and the proper repair of door and window screens.

Know The Law. Finally, legal liability appears to be changing. There are several lawsuits pending against both public and commercial entities, either for failure to prevent disease or for exposure of citizens to insecticides.