Although unlikely, pest management professionals may encounter the following medical issues. Here’s what PMPs need to know about these pests and the conditions they contribute to.
Editor’s note: Pest management professionals should never offer medical advice. PMPs always should encourage their clients to see a doctor to address pest-related health concerns. The following is for pest management professionals’ knowledge only since they may encounter such pests/conditions in the field.
There are a number of pest issues facing pest management professionals which are, in fact, human health or medical issues. In such cases, referral to a health-care provider is the best course of action. Nonetheless, this article explores these issues, contributing factors leading to such conditions and their prevention/control.
Fly larvae infesting the tissues of people or animals is referred to as myiasis. Specific cases of myiasis may be clinically defined by the affected areas involved. For example, there may be gastric, rectal, auricular and urogenital myiasis, among others. Myiasis can be accidental, for example, when fly larvae occasionally find their way into the human body (e.g., by eating an infested food), or facultative, when fly larvae feed opportunistically on decaying tissue in neglected, malodorous wounds.
Myiasis also can be obligate, in which the fly larvae must spend part of their developmental stages in living tissue. Obligate myiasis is the most serious form of the condition from a medical standpoint and is true parasitism. Fly larvae are not capable of reproduction and, therefore, myiasis should not be considered contagious from patient to patient. Transmission of myiasis occurs only from adult female flies laying eggs or (in some cases) “laying” live larvae.
Accidental Myiasis. Accidental gastrointestinal myiasis is mostly a harmless event, but the larvae could possibly survive the human gut environment temporarily, causing stomach pains, nausea or vomiting. Numerous fly species in the families Muscidae, Calliphoridae and Sarcophagidae may produce accidental enteric myiasis. Some notorious offenders are pomace flies and fruit flies (Drosophila spp.); the cheese skipper, Piophilia casei; the black soldier fly, Hermetia illucens; and the rat-tailed maggot, Eristalis tenax. One case I helped investigate was due to a child eating grapes infested with solider fly larvae. Other instances of accidental myiasis occur when fly larvae enter the urinary passages or other body openings. Flies in the genera Musca, Muscina, Fannia, Megaselia and Sarcophaga often have been reported in those cases.
Physicians occasionally use blow fly maggots to clean wounds and ulcers. “Maggot therapy” was commonly used in medicine until the advent of antibiotics in the 1940s and its use subsequently declined, but lately the practice increasingly has been used again, especially in cases where antibiotics are ineffective and/or surgery is not possible. Some European researchers recently tested the efficacy of maggot debridement vs. hydrogel, a standard medical treatment for necrotic leg ulcers, and found both treatments worked almost equally well. Time-to-healing and cost-per-treatment differences were not significantly different among the two treatments in those studies.
Facultative Myiasis. Facultative myiasis is usually not harmful (and could actually be helpful; see related article on the right) but may result in infection, pain and tissue damage if fly larvae leave necrotic tissues and invade healthy ones. Numerous species of Muscidae, Calliphoridae and Sarcophagidae have been implicated in facultative myiasis. In the United States, the blow fly Lucilia sericata has been reported as causing facultative myiasis on several occasions. Another blow fly, Chrysomya rufifacies, has been introduced into the United States from the Australasian region and is also known to be regularly involved in facultative myiasis. Other fly species that may be involved in this type of myiasis include Calliphora vicina, Phormia regina, Cochliomyia macellaria and Sarcophaga haemorrhoidalis.
Several fly species lay eggs on dead animals or rotting flesh. Accordingly, the flies may sometimes mistakenly oviposit in a foul-smelling wound of a living animal. The developing maggots may subsequently invade healthy tissue. Facultative myiasis most often is initiated when flies oviposit in necrotic, hemorrhaging or pus-filled lesions.
Facultative myiasis may occur in helpless semi-invalids who have poor (if any) medical care. Often, in the case of the very elderly, their eyesight is so weak that victims do not detect the myiasis. In clinical settings, facultative myiasis is most likely to occur in incapacitated patients who have recently had major surgery or those having large or multiple, uncovered or partially covered, festering wounds. However, not all human cases of facultative myiasis occur in or near a wound.
Obligate Myiasis. Several fly species must develop in the living tissues of a host as part of their life cycle. This is obligate myiasis and is caused by species affecting sheep, cattle, horses and many wild animals. In people, obligate myiasis is primarily due to the screwworm flies (tropical Old and New World) and the human bot fly.
Obligate myiasis is essentially a zoonosis; humans are not the ordinary host but may become infested. Human infestation by the human bot fly is often via a mosquito bite — the eggs are attached to mosquitoes and other biting flies; however, human screwworm fly myiasis is a result of direct egg laying on a person, most often in or near a wound or natural orifice. Egg-laying activity of screwworm flies occurs during daytime.
Management and Treatment. Good sanitation can avert most cases of accidental and facultative myiasis. Exposed foodstuffs should not be unattended to prevent flies from ovipositing on them. Covering and preferably refrigerating leftovers should be done immediately after meals. Washing fruits and vegetables prior to consumption should help remove developing maggots, although visual examination also should be done while slicing or preparing. Other forms of accidental myiasis may be prevented by protecting invasive medical equipment from flies and avoiding sleeping nude, especially during daytime. To prevent facultative myiasis, extra care should be taken to keep wounds clean and dressed, especially on elderly or helpless individuals.
Daily or weekly visits by a home health nurse can go a long way to prevent facultative myiasis in patients who stay at home. In institutions containing invalids or otherwise helpless patients, every effort should be made to control entry of flies into the facility. This might involve taking such precautions as keeping doors and windows screened and in good repair, thoroughly sealing all cracks and crevices, installing air curtains over doors used for loading and unloading supplies, and installing electronic ultra-violet fly traps in areas accessible to the flies but inaccessible to patients. Prevention of obligate myiasis involves avoiding sleeping outdoors during daytime in screwworm-infested areas and using insect repellents in Central and South America to prevent bites by bot fly egg-bearing mosquitoes.
Treatment of accidental enteric myiasis is probably not necessary (although there may be rare instances of clinical symptoms), as in most cases there is no development of the fly larvae within the highly acidic stomach environment and other parts of the digestive tract. They are usually killed and merely carried through the digestive tract in a passive manner. Treatment of facultative or obligate myiasis involves removal of the larvae in a variety of ways. Maggot infestation of the nose, eyes, ears and other areas may require surgery if larvae cannot be removed via natural orifices. Because blow flies and other myiasis-causing flies lay eggs in batches, there can be tens or even hundreds of maggots in a wound. Interestingly, human bot fly larvae have been successfully removed using “bacon therapy,” a treatment method involving covering the punctum (breathing hole in the skin) with raw meat or pork. In a few hours the larvae migrate into the meat and then you pull the meat off and the larvae come out with it.
Pest management professionals often encounter real or perceived mite problems when servicing accounts. Bird or rat mites can be associated with nests and spider mites can be found on indoor plants. Most of these problems are mitigated by eliminating the breeding sites and treating affected areas with a residual insecticide. However, two species of parasitic mites may actually live on people (and we can’t treat people!). PMPs should have no involvement in control of these infestations, other than perhaps providing educational materials and/or directing customers to a health-care provider.
Scabies. Scabies, or “itch,” is caused by Sarcoptes scabei. This is the most important human disease caused by mites, with about 300 million cases annually. It occurs worldwide, affecting all races and socioeconomic classes in all climates. These tiny mites burrow under the skin, leaving small open sores and linear burrows that contain the mites and their eggs. When a person is infested with scabies mites for the first time, there is generally no itch or skin reaction for about a month until sensitization develops. When that happens, there is severe itching, especially at night and frequently over much of the body. Also, large red patches or rashes may develop on the body. The mite burrows are usually located on the hands, wrists and elbows, especially in the webbing between the fingers and the folds of the wrists.
People who cannot scratch themselves and the immunocompromised (e.g., AIDS patients) may develop more serious scabies infestations in which millions of mites may inhabit thick crusts over the skin — a condition called Norwegian scabies or crusted scabies. Patients with Norwegian scabies are frequently found in personal care homes or nursing homes.
It should be noted here that animal forms of scabies such as dog or horse scabies are also caused by “races” of S. scabei, but these mites cannot live in human skin for very long lengths of time. Canine scabies can be temporarily transferred to humans from dogs, causing itching and rashes primarily on the waist, chest or forearms. However, treatment or removal of the infested dog will result in a gradual resolution of this type of scabies.
Scabies is transmitted by close, human-to-human contact with infested individuals. There is some evidence that inanimate objects may be sources of infestation or re-infestation. Touching or shaking the hands of infested persons is a major mode of transmission. The practice of several family members sleeping in one bed contributes to its spread, as does sexual activity. In addition, institutionalized children (day care) and elderly (nursing homes) seem to be contributing to an increase in the incidence of scabies. Survival of scabies mites off-host probably lasts just a day or two, more likely hours. Studies have shown the mites may survive one to five days at room conditions, but have a difficult time infesting a person after being off the host (presumably due to the mite’s weakened condition).
Treatment of scabies. Scabies should be confirmed by a physician by isolating the mites in a skin scraping, as other skin conditions may resemble scabies infestation. Scrapings should be made at the burrows, especially on the hands between the fingers and the folds of the wrists. Diagnosis can be made either by finding mites, ova or fecal pellets. Alternatively, doctors may extract mites from a burrow by gently opening the burrow with a needle and working toward the end where the tiny mites usually are.
Managing Scabies in Nursing Homes
Scabies in long-term health-care institutions, primarily for the elderly, is often a significant problem. One survey found 20 percent of 130 institutions in Ontario, Canada, had problems with scabies during a one-year period.
First, the diagnosis should be confirmed by health care staff. Frequently, scabies control measures are implemented with only weak evidence of infestation. However, implementing a large-scale control effort on the suspicion that an outbreak is occurring in the nursing home is medically and administratively unsound. The active ingredients in scabicidal creams or lotions are pesticides. A physician should be consulted to perform skin scrapings on affected patients.
Once the infestation is confirmed, treatment with a scabicidal product can be initiated. Both patients and employees with direct, close contact with affected patients should be treated. If cases reappear, aggressive treatment strategies may have to be used such as simultaneously treating all patients and employees in the nursing home and possibly even family members of all employees. Consultation with local health department epidemiology personnel is often helpful as well.
Once a scabies infestation is confirmed, treatment can be initiated. As the mites cannot live very long off a human host, insecticide treatments of bedding, furniture, rooms, etc., are unnecessary. It is recommended, however, that upon initiation of treatment, the patient’s bedcovers, pillowcases and undergarments be removed and washed on a hot wash cycle. If the patient is a child, toys, stuffed animals, etc., should be removed from human contact for a week or so.
There have been several products used for scabies treatment in the past, such as sulfur ointment, benzyl benzoate, lindane, crotamiton and thiabendazole. The most widely used products today include lindane (Kwell), permethrin (Elimite) and crotamiton (Eurax). There have been reports of lindane-resistant scabies, especially in cases of immigrants or recent travelers to Central and South America or Asia and also reports of serious, even fatal, adverse effects on the nervous system from misapplication of lindane. Regardless of the product used, all package instructions should be followed carefully.
For most scabicides, the product is applied to the entire body, except the head (see package insert; sometimes the head is treated) and left on for 14 to 48 hours depending on instructions. After that, a cleansing bath may be taken. A second treatment may be called for in the instructions. Itching may persist for weeks or more after treatment and does not necessarily indicate treatment failure.
Follicle Mites. Although there are numerous species of Demodex mites infesting wild and domestic animals, only two species are specific human-associated mites and are called follicle mites. These minute, wormlike mites live exclusively in hair follicles or sebaceous glands. As far as is known, they cause no harm to humans, although some researchers have attributed certain conditions of the skin to Demodex. Doctors should be aware of mite appearance, as they may be seen during skin-scraping examination.
In general, Demodex folliculorum lives in the hair follicles and D. brevis in the sebaceous glands. Both species are similar in appearance (with the exception that D. brevis is a shortened form) and are elongated, wormlike mites with only rudimentary legs. They are about 0.1 to 0.4 mm long and have transverse striations over much of the body. These mites most commonly occur on the forehead, malar areas of the cheeks, nose and nasolabial fold, but they can occur anywhere on the face, around the ears and occasionally elsewhere. Most people acquire Demodex mites early in life from household contacts — primarily their mother. Unless a physician deems treatment necessary for a particular case, follicle mite infestations should be considered normal or natural and left alone.
Head Lice and Pubic Lice.
Lice are ectoparasites of animals that either eat skin/fur/feathers (chewing lice) or suck blood (sucking lice). There are three species of lice that may infest humans, two of which will be discussed here. As is the case with parasitic mites, human lice problems are a medical issue that PMPs should avoid. However, especially in the case of head lice, PMPs are bombarded with questions about their biology and control.
Lice Resistant to Medicinal Creams or Shampoos
In recent years, there has been an increase in reports of head lice treatment failures. These failures are most often the result of re-infestation or lack of adherence to already established treatment protocols. However, there does appear to be development of resistance in certain lice populations to conventional agents such as permethrin, pyrethrins and organochlorine insecticides. In the U.S., in particular, lice have become increasingly resistant to pyrethroids and lindane, but not to malathion. One study of field-collected lice from Buenos Aires showed definite resistance to permethrin. However, it is unlikely that any particular population of lice is resistant to all pediculicides. Patients with suspected populations of resistant head lice should switch and be treated with a product containing a different class of active ingredient, again paying careful attention to label directions. The patient must be treated with a product containing a different chemistry.
Recently, some physicians have chosen to treat head lice cases with ivermectin, which has been shown to be extremely effective in treating resistant head lice. Ivermectin is an antiparasitic drug discovered in the early 1970s that is a derivative of avermectin B1, a compound produced by Streptomyces avemitilis. It is a systemic parasiticide/acaricide, meaning you take it as a pill and then it kills the pests as they feed on their host.
Head Lice. Head lice (singular = louse), Pediculus humanus capitis, are similar to body lice (not covered here), except they are confined to the scalp. Head lice have been pests of humans throughout the ages, as evidenced by the discovery of ancient hair combs dating back to the first century b.c. containing the remains of lice and their eggs. The number of cases of head lice has increased worldwide since the 1960s, with hundreds of millions of cases now recognized annually. In the United States about 6 to 12 million people are treated for head lice each year. Head lice generally pose no health threat, although heavily infested persons complain of severe itching and often have swollen lymph nodes on the neck. The primary negative effects of lice infestation are embarrassment and social sanctioning.
Head lice occur worldwide and are tiny (1 to 3 mm long), elongated, soft-bodied, light-colored, wingless insects. They are dorsoventrally flattened, with an angular ovoid head and a nine-segmented abdomen. The head has a pair of simple lateral eyes and a pair of short five-segmented antennae. Head lice possess specially modified claws that enable them to grasp tightly to hair shafts while they feed through their piercing/sucking mouthparts. Head lice look almost identical to body lice. However, they vary distinctly in behavior; head lice occur chiefly on the head, whereas body lice occur on the body and clothing. Head lice eggs (called nits) are about 1-mm long oval objects with a distinct cap on one end. They are white to cream-colored when viable and firmly attached to the hair. By the naked eye they can be confused with dandruff, globules of hair oil or hairspray and other substances, but they are easily identified with a hand lens or microscope.
Head lice live on the skin among the hairs on the patient’s head. Nits are laid on the shaft of the hair, near the base and attached with a strong glue-like substance. As long as adult lice remain on the scalp, they can live for about a month. Because they require the warmth and blood meals afforded by the scalp, it is generally reported that lice can survive only about 24 hours if removed. But in one study involving hundreds of head lice removed from children, none survived longer than 15 hours; most died between 6 to 15 hours. This is important because it demonstrates that lice do not live long off their hosts.
Treatment and control of head lice. Head lice problems are not to be handled by pest control personnel; this is strictly a medical issue. Management of head lice infestations requires three basic steps: (1) delousing infested individuals with various pesticidal lotions or shampoos, with retreatment as necessary; (2) removing nits from the hair as thoroughly as possible; and (3) delousing personal items (clothes, hats, combs, pillows, etc.). An important principle of head lice management is to treat all infested members of a family concurrently. If an infested school-aged child is the only family member treated, he or she may be quickly re-infested by a sibling or parent who is also unknowingly infested. Just about any brand of louse control products, even those containing lindane (still available in some countries), are generally safe when used as directed. No matter which product they choose, patients should be instructed to follow the precautions and instructions on the product labels.
Finally, efforts should be made to delouse personal belongings of infested individuals. Very rarely a pest control professional may sometimes be involved in this process. Washable clothing, hats, bedding and other personal items should be washed properly and dried in a clothes drier for at least 20 to 30 minutes. Non-washable clothes should be dry-cleaned. Other personal items such as combs and brushes should be thoroughly washed in one of the pediculicidal products or soaked in hot water (130°F or more) for 5 to 10 minutes. Upholstery exposed to potential infestation should be vacuumed thoroughly. Use of certain appropriately labeled pyrethrin aerosols on furniture, carpeting and other places where lice are suspected may kill a stray louse or two, but as the lice do not willingly leave their host and do not survive long off the host, these treatments are just a psychological adjunct to other treatments and generally are not recommended. Also, pyrethrin aerosols for environmental decontamination may cause asthma in allergic individuals and should never be used on or near the head.
Non-Pesticidal Lice Control. Non-pesticidal treatments for head lice include shaving the head, coating the hair with a thick layer of mayonnaise or petroleum jelly, various combinations of lice combs/conditioners (wet hair combing) and hot-air machines. Anecdotal reports indicate that mayo or petroleum jelly indeed kills/smothers lice, but must be left on a long time and is extremely difficult to subsequently remove from the hair. (One person told me that she had to wash her hair more than 200 times to remove all of the petroleum jelly.) More recently, a product called Ulesfia has become available, which suffocates the lice in a manner similar to petroleum jelly, but works faster. Two treatments are still required about a week apart to kill any newly hatching lice. Wet-combing of the hair of lice-infested individuals along with conditioners has been advocated for several years by the U.K. Charity Community Hygiene Concern.
“Bug Buster” kits containing fine-toothed lice combs and conditioner have been developed by the Community Hygiene Concern and used in several locations in England, Wales and Scotland. One study with the Bug Buster kit showed it to deliver a 57 percent cure rate against head lice. Hot air, delivered from a variety of hair dryers, has been proven effective against head lice, although the Lousebuster was most effective, resulting in nearly 100 percent mortality of eggs and 80 percent mortality of hatched lice after treatment by experienced operators.
Pubic or Crab Lice. Pubic lice infestations are known as pediculosis pubis or pthiriasis and is caused by Pthirus pubis. The lice occur almost exclusively in the pubic or perianal areas, rarely on eyelashes, eyebrows or other coarse-haired areas. They feed on human blood through piercing/sucking mouthparts. The bites may cause intense itching due to the host’s reaction to proteins in louse saliva and extensive scratching may lead to inflammation of the skin and lymph glands due to bacterial infection. If infestation occurs in the eyelashes, there may be inflammation of the eyelids. Pubic lice are not known to transmit disease organisms. However, pediculosis pubis frequently coexists with other venereal diseases, particularly gonorrhea and trichomonas. One study indicated one-third of patients with pubic lice may have other sexually transmitted diseases.
Pubic lice occur on humans worldwide. The adults are dark gray to brown in color and are called crab lice because of their crablike shape. They are distinctly flattened, oval and much wider than body or head lice. As with head and body lice, the head bears a pair of simple lateral eyes and a pair of short five-segmented antennae. They are 1.5 to 2.0 mm long; their second and third legs are enlarged and contain a modified claw with a thumb-like projection, which aids them in grasping hair shafts. The individual egg, or nit, is dark brown in color and smaller than that of the body louse.
Pubic lice require blood to survive, are only found on humans and do not infest rooms, carpets, beds, pets, etc. If lice happen to be forced off their host, they will die within 24 to 48 hours. Female pubic lice deposit their eggs (nits) mainly on the coarse hairs of the pubic area and rarely on hairs of the chest, armpits, eyebrows, eyelashes and mustache. Pubic lice do not fly, jump, or even crawl very much. They often spend their entire life feeding in the same area where the eggs were deposited.
Treatment of pubic lice. As pubic lice infestations are usually transmitted through sexual contact, it is important to have the sexual contacts of the infested person examined and treated if needed. Likewise, as some family members all sleep in the same bed, if one member of a family has an infestation, all family members should be examined and treated if necessary. As with head and body lice control products, pubic lice control products are sold over-the-counter, but some are by prescription. Treatments should closely follow directions on the box, bottle or package insert. As is the case with head and body lice, oral ivermectin has been proposed as an effective treatment for pubic lice, although to date the U.S. Food and Drug Administration has not approved the product for use as a pediculicide. At the same time of treatment (no matter which one), infested persons should wash all their underclothes and bedding in hot water for 20 minutes or more and dry them on the hottest setting. Because of the limited survivability of pubic lice off their hosts, insecticidal sprays, fogs, etc., in the patient’s home, work or school are not necessary.
All photos (except top photo) are courtesy of the author.
Goddard is the author of “The Physician’s Guide to Arthropods of Medical Importance.” He is an extension professor of medical and veterinary entomology at Mississippi State University. E-mail him at firstname.lastname@example.org.