The Topic of This Month Vol.20 No.6(No.232)
Lice infesting only humans include three species; the head louse infesting human heads (Pediculus capitis), the body louse infesting undergarments or clothing in contact with a human body (P. humanus), and the pubic louse infesting mainly the pubic hair (Pthirus pubis). The head louse and the body louse are different each other in ecological character but morphologically almost indistinguishable. Body lice are vectors of Rickettsia prowazekii, Borrelia recurrentis, and Bartonella quintana, the etiological agents of epidemic typhus, relapsing fever, and trench fever, respectively. Historically, a large number of people have died of these infectious diseases. Although neither head lice nor pubic lice are directly concerned with transmission of these pathogenic rickettsial agents, their infestation, causing dermatitis accompanying severe itching and mental stress, is a nuisance. The transmission is caused by direct contact of the hair with an infested person in the case of head lice, that of the body with infested persons or clothing in the case of body lice, and sexual contact in the case of pubic lice.
Recently, cases of pediculosis capitis (head lice infestation) among children are likely to increase in the whole country. In addition, cases of pediculosis corpolis (body lice infestation) have increased among homeless people having expanded recently in urban areas (see p. 135 of this issue). Cases of pediculosis pubis (pubic lice infestation) have recently been reported also in urban areas. The following is a summary of surveys and control focused on pediculosis capitis, since the data available on pediculosis corpolis and pubis are too few to be included in this summary.
Pediculosis capitis and its surveys in Japan
As was the case in other developed countries, the number of lice-infested people has tremendously decreased due to the thorough application of insecticides such as DDT during the post-World War II period, obvious improvement in public health and environmental health, and the Japanese life style keeping the bodies clean. In response to the 1971 ban of organochlorine insecticides such as DDT and BHC, pediculosis capitis broke out among nursery school, kindergarten and primary school children and human lice infestation re-emerged in Japan.
Head louse infestation reports (including consultations) gathered by local governments and health centers are forwarded by each prefecture to the Waste Management Division, Water Supply and Environmental Sanitation Department, Environmental Health Bureau, Ministry of Health and Welfare. Since 1981, the above reports have been compiled in the "prevalence of rodents and insect pests". According to those data, the number of incidents of pediculosis capitis was the largest, being about 2,300 involving about 24,000 cases, in 1982 (Fig. 1). In connection with the marketing and the use of chemotherapeutic agents of pyrethroid insecticide for lice control in 1982, this incident peak gradually lowered to about 200 involving 1,900 cases in 1987. During the several years thereafter, the incidence was kept on a low level, but started to increase again in 1991, showing a small peak containing about 7,500 cases in 1992, followed by an even level of about 5,000-6,000 cases per year for several years. After 1994, however, incidents of pediculosis capitis are likely to increase.
According to the most recent data of incidence of pediculosis capitis in 1997, there were 3,163 incidents, a 44% increase, and 8,641 cases, a 50% increase from the preceding year (Table 1). In 1997, about 330,000 packages of medicine against head lice (one package contains the dosage for one course per case) were marketed, exceeding the sales in the preceding year by 28%. This indirectly indicates the recently increasing tendency of pediculosis capitis and it is anticipated that only few of pediculosis cases are reported.
Pediculosis capitis cases may be found all through the year, but a bimodal tendency in monthly incidents with peaks in June and October is shown (Fig. 2). Analysis of the incidents by place of infestation tells that many cases are recognized at nursery schools, kindergartens, and primary schools, where there is a direct, physical intercourse (Table 1). Such a tendency that infants and children younger than 12 years old are vulnerable to pediculosis capitis is seen every year during the past six years (Table 1).
Transmission and control of head lice
The routes of transmission include direct contact of the heads as the main route and common use of bedding, towels, caps, and lockers among community and family members as well. Therefore, prevention and control of head lice infestation must depend on avoidance of common use of towels and combs and the use of hot water (higher than 55C) to wash clothes, sheets, pillow covers, and caps. In addition, early finding of adult lice and louse eggs (nits) by careful examination of the hair is also important. If lice are found within family or community members, some control measure suitable for delousing should be taken in an appropriate scale all at once.
To exterminate human head lice, powder formulation of pyrethroid fenothorin was marketed in 1981 and shampoo formulation of fenothorin in 1998, both of which are in wide use in Japan. On the other hand, insecticides belonging to organochlorine, organophosphorus or pyrethroid are being used widely in other countries to exterminate body lice and head lice. However, the development of resistance to louse-control chemicals is becoming a serious problem in other countries (see p. 135 of this issue).
For physical removal of human head lice, shampooing and combing are effective, but 100% effect can not be expected. In contrast to the current delousing depending on chemicals, such traditional methods as the use of combs for removal of lice (adult lice and nits) are being reconsidered in UK and USA. A campaign promoting the use of combs is being held by public and private organizations (see p. 135 of this issue).
Conclusion: The increase in Pediculus capitis infestation in developed countries may not be ascribable merely to the poor hygienic conditions due to poverty. As the factors contributing to the increase in cases of pediculosis capitis in Japan, considered are such multifactors as follows: increased global exchange of people, lack of awareness of lice infestation in children due to the increased new generation parents who have never seen lice, and the possible development of resistant lice to insecticides. As the conditions affecting lice infestation, such multifactors as season, sex, length of the hair, family size and density, familial infestation level, means of attending school, congestion of desks in classrooms, and sitting on the floor may take part in complicatedly. Thus, pediculosis capitis in developed countries including Japan should be regarded as a public health problem changeable depending upon life style and behavior associated with louse infestation in urban areas. For control of pediculosis capitis (see the note below) prevailing among school and kindergarten children, the provision of adequate information and education on lice infestation are necessary and extensive public health activities in cooperation with physicians, school teachers, local public health officials and family members are required.
Note: Pediculosis capitis often creates problems of school health. In a reference material drawn up by the Ministry of Education, Science, Sports and Culture in compliance with the partial amendment of the enforcement regulation for the School Health Law (in April 1999), it is referred to a communicable disease, the patients of which do not have to avoid attending school.