Middle East DVEP - Armed Forces Pest Management Board

The survival of R. prowazekii between outbreaks is of interest, since there is notransovarial transmission and lice die from the infection. A milder form of epidemictyphus known as Brill-Zinsser disease occurs in individuals who recover from the initialinfection and relapse years later. Lice feeding on such patients become infected. Theserelapsed individuals are considered to be the main reservoir of R. prowazekii in easternEurope. A sylvatic cycle of R. prowazekii has been recognized in the southeastern UnitedStates, where flying squirrels and their ectoparasites (the flea Orchopeas howardii andthe louse Neohaematopinus sciuropteri) are naturally infected. The louse is host specific,but O. howardii has an extensive host range, which includes humans. Sporadic humancases have occurred in houses harboring flying squirrels. The significance of this findingto the epidemiology of epidemic typhus in other areas is not known.Vector Ecology Profile. Human lice spend their entire life cycle (egg, 3 nymphal stagesand adult) on the host. Eggs of body lice are attached to clothing at a rate of about 5 eggsper female per day. At 29 o to 32 o C, eggs hatch in 7 to 10 days. The maximum time eggscan survive unhatched is 3 to 4 weeks, which is important when considering the survivalof lice in infested clothing and bedding. A bloodmeal is required for each of the 3nymphal molts and for egg production in adults. The nymphal stages are passed in 8 to16 days. Louse populations have the potential to double every 7 days. Adults live about2 weeks and feed daily. Infestations of lice cause considerable irritation and scratching,which may lead to skin lesions and secondary infections. Body lice are commonly foundin the seams and folds of clothing. Lice tolerate only a narrow temperature range andwill abandon a dead host or one with a body temperature of 40 o C or above. Thiscontributes to the spread of lice and louse-borne disease. Human lice can survive withouta host for only a few days.Vector Surveillance and Suppression. Surveillance for body lice consist of examiningindividuals and their clothing for lice or nits (eggs). Body louse infestations havedeclined with higher standards of living, although infestations are still common in someMiddle Eastern populations. Military personnel should avoid close personal contact withinfested persons and their belongings, especially clothing and bedding. Dry cleaning orlaundering clothing or bedding in hot water (55 o C for 20 minutes) will kill eggs and lice.Control of epidemics requires mass treatment of individuals and their clothing witheffective insecticides. The permethrin-treated BDU is extremely effective against lice.Since lice cannot survive away from the human host, application of insecticides tobuildings, barracks or other living quarters is not necessary.E. Relapsing Fever (louse-borne). (Epidemic relapsing fever)Louse-borne relapsing fever is caused by the spirochete Borrelia recurrentis. Thesymptoms and severity of relapsing fever depend on the immune status of the individual,geographic location, and strain of Borrelia. The incubation period in an infected hostranges from 2 to 14 days. The disease is characterized by a primary febrile attackfollowed by an afebrile interval and one or more subsequent attacks of fever andheadache. Intervals between attacks range from 5 to 9 days. In untreated cases, mortalityis usually low but can reach 40%. Infection responds well to treatment with antibiotics.80