SECTOR WIEWS Vol

^^^<.-^-< SECTOR WIEWS Vol. 18 No. 5 May, 1971 -311^ UNDERSTANDING,6 AND TREATING INFESTATIONS OF LICE ON HUMANS Benjamin Ken and John H. Poorbaugh, Ph.D. Infestation with human lice, or pediculosis, Therefore, sucking lice found established still occurs even in societies with generally upon humans can only be human lice, of which high standards of sanitation. Public health there are three distinct kinds: head lice, body agencies may become involved if infestations lice, and crab lice. More than one of these include or expose a substantial number of peo- kinds may infest a person at the same time. ple, which occasionally happens especially at public institutions such as Jails, schools, The common and scientific names of human and state or county hospitals. lice now accepted by the Entomological Soci- ety of America (Blickenstaff, 19 70) and sever- This compilation is presented as a guide al common synonyms found in the older litera- to the accurate and recognition proper treat- ture are: ment of those occasional infestations of human lice which still annoy and potentially 1.) head louse Pediculus humanus threaten our citizens. capitis De Geer Identification and Biology of Human Lice synonym Pediculus capitis De Geer Human lice are part of a rather large group 2.) body louse Pediculus humanus hu- of insects known as sucking lice which are manus Linnaeus permanent parasites on the bodies of mammals synonyms Pediculus humanus corpo- throughout the world. These insects spend ris De Pediculus corporis De their entire life on the bodies of their animal Geer; Geer; Pediculus vestimenti Nitzsch hosts where they suck blood for nourishment and obtain necessary moisture and warmth. 3.) crab louse Pthirus pubis (Linnaeus) The eggs of lice, which are called nits, are attached to the hair of the host, and in the synonyms - Phthirus pubis (Linnaeus); c ase of the human body louse, to clothing Phthirius pubis (Linnaeus); Phthirius fibers. Many different kinds of sucking lice inquinalis Leach are found on warm-blooded animals throughout the world, and each kind of louse is close- It is important that an accurate identi- ly adapted to and is often restricted to a cer- fication of the louse involved be made so that tain kind of animal. Human lice can establish the most effective treatment and preventive and maintain themselves only on humans. measures can be recommended. In some in- stances, errors in diagnoses of pediculosis Vector Control Specialist, Bureau of Vector Con- have been made on the basis of inconclusive trol and Solid Waste Management, California State evidence, particularly when head lice have Department of Public Health. been suspected. Head lice and body lice are different forms The head louse usually attaches the nit (subspecies) of the same louse species, Pedi- close to the base of the hair about 1 mm from culus humanus, and are superficially similar the scalp (Nuttall, 1918). The hair is assumed in appearance, but both are easily distinguish- to grow at the rate of 0.4 mm per day (Mellan- able from the crab louse with the aid of a mag- by, 1942). Since the nits of the head louse nifying glass. Body and head lice have the hatch in about nine days one would expect three pairs of legs about equal in size, and the most of the unhatched nits to be within 5 mm abdomen is distinctly longer than wide (Figure (about 3/16 of an inch) from the scalp. Empty 1). The crab louse has the middle and hind shells which lack the cap and are no longer legs and claws greatly enlarged, and the abdo- turgid to the touch are likely to be farther men is wider than long, giving the creature a from the scalp. crab-like appearance (Figure 2). The nits of head lice (Figure 3) and body Adult body and head lice are approximately lice (Figure 4) are quite similar in appearance, 2 mm (males) to 3 mm (females) in length and but those of crab lice (Figure 5) are slightly vary in color from dirty white to greyish-black. smaller, have prominent respiratory globules Head lice can adapt their coloration somewhat on the cap, and have a longer cement attach- to the hair color of the host, so that lice from ment on the hair.. The fact that the nits are blondes tend to be paler than those from peo- cemented at an oblique angle to the hair ple with dark hair. Body lice and head lice are (like a stubby branch) is very helpful in dis- quite similar in appearance, and even an ex- tinguishing them from foreign material which pert will have difficulty in positively distin- frequently surrounds the hair and may readily guishing between all specimens of the two on slide up and down. the basis of morphology alone. However, t heir habits differ significantly. Head lice. almost Lice, as well as hairs bearing louse nits, always live in the head hair and attach their can be preserved in alcohol and submitted to nits (eggs) to the hair. Body lice prefer to live an entomologist for identification or verifi- in the clothing and attach their nits-to cloth- cation of a diagnosis. The Bureau of Vector ing fibers (infrequently to the body hair). Control and Solid Waste Management will make such determinations for California health per- Adult crab lice are greyish-white to slight- sonnel. ly pink and are only about 1 mm long. Crab lice mainly infest the pubic hair, occasionally the The body louse: The body louse has been the hair elsewhere on the body, and attach their object of much attention. It alone, among the nits only to hair. three kinds of human lice, has been definitely implicated as a vector of louse-borne relaps- Immature lice (nymphs) look very much ing fever and epidemic typhus. Historically, like the adult but are smaller. There are three the massive epidemics of louse-borne diseases growth stages or instars between the nit stage were transmitted by large populations of body and the adult. Immature crab lice are easily lice which infested people living in unsanitary separable from immature head lice and body conditions, especially during times of famine, lice, but the young of head lice and body lice disaster, or war. Although there is some ex- look very much alike. perimental evidence that both the crab louse and the head louse might serve as vectors, Human lice attach their nits firmly to hair their actual role as such has not been estab- or clothing fibers by a ring of cement. The lished. Neither of the two louse-borne diseases nits are about 0.8 mm long and 0.3 mm wide, has been reported in the United States for the thus two nits placed end-to-end would cover past 35 years. The bites of the body louse are the diameter of the head of an ordinary pin. annoying, and the skin of persons who con- The nits are oval in shape and yellowish opal- tinuously .harbor these lice becomes hardened escent in color. Each nit has a cap (operculum) and darkly pigmented, a condition known as which comes off intact when it hatches. After "vagabond's disease". the nit has hatched, the cement-like attach- ment and empty shell may remain on the hair. All stages of body lice are found on cloth- These empty shells are not easily removed by ing. The adults and nymphs move to the skin shampooing or washing, and thus are useful at intervals to feed and are most numerous in diagnosing lousiness even if hatched lice where clothing is in continuous close contact are not located. with the body, such as the armpits and belt- It 1 JAN107? 24 I mm FIGURE 1 FIGURE 2 Pedicalus husnanus capitis, head louse. Pthirus pubis, crab louse- mm 1 mm FIGURE 3 FIGURE 4 FIGURE 5 Nit or egg of head louse Nit or egg of body louse Nit or egg of crab louse attached to head hair. attached to clothing attached to pubic hair. fibers. Illustrations taken from Matheson, R., 1950, Medical Entomology, by permission of Cornell University Press, except Figure 4, from Ferns, G. F., 1951, The Suck- ing Lice, by permission of the Pacific Coast Entomological Society. 25 line. The number of lice that normally occur The head louse: Although there is no sub- on an infested person is usually a dozen or so, stantial evidence that under natural circum- but an occasional individual may harbor hun- stances head lice are vectors of human dis- dreds or even thousands of lice. ease, their status as annoying ectoparasites of man is sufficient reason to consider them A female body louse may lay 200 or more undesirable and to justify the effort to elimin- nits at a rate of 10 per day. One generation re- ate them. Head lice and their nits are usually quires on the average about 3 weeks to com- found in the hair behind the ears and on the plete. In experiments with body lice under nape but also may be found in headgear and laboratory conditions, Busvine (1948) found possibly on hair elsewhere on the body. The the nit incubation period at 30C to be 8 to incidence of head lice seems to be greater 10 days, and when held 24 hours on the host among individuals with long hair or dense the combined nymphal periods averaged 8.3 hair than in persons with short or sparse hair. days, and the adults survived for about 20 They are most frequently found on the young, days. These time periods may be prolonged the old, and the incapacitated, who are un- under natural conditions, as for example when able to groom themselves effectively.

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