|Emergency Vector Control after Natural Disaster (PAHO)|
|Part II: Control measures for specific vectors|
|Chapter 8: Flies, rodents and other vectors|
Lice, fleas, mites, ticks and other arthropods may produce serious problems following natural disasters, (see Annex III). The lice of medical importance belong to the order Anoplura, or sucking lice. The important species are the crab louse, Pthirus pubis, the head louse, Pediculus capitis, and the body louse, Pediculus humanus. Of these, Pediculus humanus is the only species that is an important vector. It is the only proven vector of two diseases, louse-borne (epidemic) typhus and epidemic relapsing fever, a spirochete disease. Pediculus humanus and other lice can also cause a great deal of discomfort through their bites.
Surveys of human lice, with a reasonable population sample, should be conducted in order to determine the extent of the problem and the number of individuals who require treatment, and to determine the effectiveness of the control program. A louse survey involves searching for the insects and their eggs, or nits. Body lice are found on shirt collars, the waistband, pockets and seams of trousers, and the seams of underwear. Head lice are normally found in the hair of the head, particularly around the ears and nape of the neck. The nits of head lice found within 7 mm of the scalp may be considered viable. Crab lice are usually found in the pubic and perianal areas of the body.
There must be a quick reaction to a serious increase in body louse infestations, with the threat of an epidemic outbreak of disease. In an emergency, the method of choice is that of mass delousing of the population with insecticide dust delivered by a compressed air duster. Use of cans with holes punched in one end will also suffice. Since there is widespread resistance to DDT, the dusting powders of choice include temephos (Abate), malathion, or gamma HCH (lindane). If time permits, the effectiveness of various pesticides should be assessed with the World Health Organization's insecticide susceptibility test. In emergency camps, clothing fumigants such as HCN, methyl bromide or ethyl formate can be used if the fumigation is supervised by properly trained personnel. Mass laundering of clothing is effective only if a water temperature of 52°C or more can be maintained. It is necessary to alert the population through public education to the dangers of louse-borne diseases and the need for mass delousing.
Head lice are not important as disease vectors, so that mass treatment may only be necessary when the prevalence is extremely high. Lotions or shampoos of malathion, pyrethrins or gamma HCH provide effective treatment. When school children are infested, treating of all family members is recommended for successfully controlling infestation. Crab lice that are not disease vectors, may be treated on an individual basis using shampoo, lotion or creme formulations of malathion gamma HCH, or pyrethrins.
Fleas belong to the order Siphonaptera. In the adult stage, all known species are obligate parasites. A number of these feed on the blood of man and his domestic animals. The most important diseases transmitted by fleas are plague and murine (endemic) typhus. Both of these diseases have host reservoirs so that attempts to eliminate the vectors should be coordinated with rodent control programs. Fleas can be collected by hand from the bodies of infested persons or animals. They can also be removed by combing small wild animal hosts, or trapped alive and anesthetized or killed. If a plague outbreak is imminent, rodent runs and burrows should be dusted and bait boxes should be rinsed with carbaryl or diazinon dust. The mass rodent control should begin only after flea populations have been eliminated, so that newly emerged fleas, deprived of their normal hosts, will not seek humans.
Mites are small, sometimes microscopic organisms that belong to the class Arachnida. Although they transmit diseases such as scrub typhus and Q fever, in times of natural disasters the disease is not an important factor. The annoyance created by itching and dermatitis can, however, be important. When people are crowded and mammals and birds share the same conditions with man, these animal ectoparasites may flow over to man. Sudden epidemics of the "itch" may thus occur in refugee or temporary camps. An attempt should be made to find the cause of the problem. Ointments exist which can be used to treat individual cases, but the best method of solving the problem is to improve sanitary habits and remove the animal source.
The mite, Sarcoptes scabiei, causes an infectious disease of the skin called scabies. In scabies, the penetration of the mite can be seen in visible papules or vesicles, or tiny linear burrows which contain the mites and their eggs. Scabies may be widespread during disasters. This is particularly true in developing countries. The disease is transmitted through prolonged intimate contact with scabietic skin, especially during sexual intercourse. Treatment on a coordinated mass basis involves the use of gamma HCH, crotamiton (Eurax), precipitated sulfur in petrolatum, or an emulsion of benzyl benzoate. A second course of treatment is necessary within seven to ten days. Case finding efforts should be extended to the screening of whole families, and soap and facilities for mass bathing and laundering should also be made available.
Ticks belong to the order Acarina. Ticks are vectors of Rocky Mountain Spotted Fever, Colorado Tick Fever, Q fever, tick-borne relapsing fever and several other diseases. Certain species also cause tick paralysis. Tick surveys involve either collecting specimens from wild animal hosts, or using a tick drag. A tick drag is a piece of white flannel which is slowly pulled over the vegetation along trails and road ways for a specific distance, and is then examined. A tick problem can be reduced by clearing the vegetation fifty to one hundred feet around a refugee camp. In chemical control, an area is treated with an insecticide such as chlorpyrifos or tetrachlorvinphos.
Ants, spiders and scorpions may cause problems, especially during flooding. Since these arthropods seek high ground, they often invade houses and other shelters. Their bites can be painful; some produce intense suffering for which therapy must be considered. Health education may help to alert people of this danger. Through such efforts people should be asked to shake out clothing, check shoes before dressing and turn back bedding before retiring. Removal of debris and improvement of all general sanitation can also be of help. Insecticides can be used, especially in temporary housing, to limit the problem. Severe infestations of bedbugs may also occur under crowded conditions. Bedbugs can be easily eliminated by spraying malathion in infested areas with a hand compressed air sprayer.
Poisonous snakes seek high ground during flooding and may enter houses. The chance that they will come into contact with man is therefore increased. Occupied areas should be cleaned of debris and grass should be kept as short as possible. Universal antivenin should be available for members of the staff who clear debris, for vector control field staff, and at temporary housing camps.