Inna Ioffe-Uspensky

Permethrin resistance in the head louse Pediculus capitis from Israel

Head lice, Pediculus capitis, were collected from children aged 3–12 years in Maale Adumin, a town near Jerusalem, after reports of control failure with the pyrethroid insecticide permethrin. A total of 1516 children were examined: living lice and eggs were found on 12.1% of the children; or another 22.8% of the children only nits were found. Twice as many girls as boys (8.1% v 4%) were infested with lice and or nits. Head lice collected from infested children were exposed to permethrin impregnated filter‐papers. Log time probit mortality (ltp) regression lines were calculated for mortality data and compared to ltp lines for a similar collection of head lice made in 1989. The regression lines for the two years were significantly different, with a 4‐fold decrease in susceptibility at the LT50 level between 1989 and 1994. The slopes of the lines also suggested that the 1994 population was more heterogenous in its response to permethrin than the 1989 population. In contrast, a laboratory population of body lice (Pediculus humanus) tested with the same batch of permethrin‐impregnated papers showed a slight but non‐significant increase in susceptibility between 1989 and 1994. The results suggest that resistance to pyrethroids has developed rapidly among head lice since permethrin was introduced in 1991 as a pediculicide in Israel.

Louse Comb Versus Direct Visual Examination for the Diagnosis of Head Louse Infestations

Abstract: The techniques used for diagnosis of head louse (Pediculosis capitis) infestation are a source of controversy. Most epidemiologic and diagnostic studies have been done using direct visual examination. The main objective of this study is to compare the efficacy of direct visual examination versus the louse comb method. The hair of each child was examined twice; one team used a screening stick and another team used a louse comb. Seventy‐nine boys and 201 girls, 7–10 years old were examined. Examination with a louse comb found that 25.4% of the children were infested with both lice and nits, while another 31.3% had nits only. Boys were significantly less infested with lice and nits than girls (lice: 15.2 and 29.6%; nits: 21.5 and 35.4%, respectively). The infestation rate with lice and nits was significantly higher in children with long (68.9%) and medium‐length (63.9%) hair than in children with short hair (44.0%) (p < 0.01). Direct visual examination found that 5.7% of the children were infested with both lice and nits, and another 49.0% with nits only. The average time until detection of the first louse was 57.0 seconds with the comb as compared to 116.4 seconds by direct visual examination. Diagnosis of louse infestation using a louse comb is four times more efficient than direct visual examination and twice as fast. The direct visual examination technique underestimates active infestation and detects past, nonactive infestations.

The dog factor in brown dog tick Rhipicephalus sanguineus (Acari:Ixodidae) infestations in and near human dwellings

Three cases of the tick Rhipicephalus sanguineus infiltration in or near human dwellings caused by dogs, and their influence on epidemiological features of human habitats have been investigated. (a) The observation of dogs kept indoors proved that single tick females could engorge and oviposit inside apartments followed by the development of subadults. (b) Abundant micropopulations of ticks were formed in small yards or gardens near the dwellings where dogs lived in kennels. (c) A huge field population of R. sanguineus was observed on a farm where watchdogs constantly patrolled along the farm perimeter. Tick abundance near the kennels and in the permanent resting sites of the dogs reached more than 30 adults per 10 min of collecting, while the number of adults on a dog reached 100. Unfed adult females under conditions of constant dog availability had a larger scutal index than females collected in the control field site. On the basis of circumstantial evidence it is possible to conclude that under the above conditions tick development may change from the normal 3-host cycle to a 2-host cycle. Ticks in the field had one complete generation per year. Ticks on the farm, as well as ticks in kennels, developed faster and a significant part of their population had two complete generations per year. R. sanguineus is the main vector and reservoir of a pathogen from the Rickettsia conorii complex, the causative agent of Israeli tick typhus. The described conglomerations of R. sanguineus create a great risk to humans who can be attacked by infected ticks in and around their homes, even in large towns. Such a feature of the tick life history most likely exists not only in Israel but in other countries as well.

Prevalence of Vectors of the Spotted Fever Group Rickettsiae and Murine Typhus in a Bedouin Town in Israel

Abstract A survey of the vectors of spotted fever group Rickettsiae and of murine typhus was carried out in Rahat, a Bedouin town in the Negev Desert, where the diseases are endemic. Houses with known cases of spotted fever group Rickettsiae or murine typhus were compared with those without reported clinical cases. A neighboring Jewish community, Lehavim, where no cases of spotted fever group Rickettsiae and murine typhus were reported in recent years, was used as a control. In the houses of patients with spotted fever group Rickettsiae in Rahat, an average of 7.4 times more ticks were found than in control houses. Out of 190 ticks isolated from sheep and goats or caught by flagging in Rahat, 90% were Rhipicephalus sanguineus (Latreille), 7.9% Rhipicephalus turanicus Pomerantzev, and 2.1% were Hyalomma sp. In the houses of patients with murine typhus, three times more rats were caught and, on the average, each rat was infested with 2.2 times more fleas than rats in the control houses. Out of 323 fleas collected from 35 Norwegian rats (Rattus norvegicus Berkenhout), 191 were Xenopsylla cheopis Rothschild and 132 Echidnophaga murina Tiraboschi. Thus, there was a six to seven times higher probability of encountering a tick or flea vector where infections had occurred than in control houses in Rahat. The percentage of rats seropositive to Rickettsia typhi was similar in study and control households (78.3 and 76.2, respectively). In the control settlement, Lehavim, only three Mus musculus L. were caught, which were not infested with ectoparasites and their sera were negative for murine typhus. Out of 10 dogs examined in this settlement, 15 R. sanguineus and eight specimens of the cat flea (Ctenocephalides felis felis Bouché) were isolated. No rats were caught in this settlement. These data indicate that there is a correlation among the density of domestic animals, their ectoparasites, and the incidence of spotted fever group Rickettsiae and murine typhus in Rahat.

Body weight characteristics of some ixodid ticks: Reflecting adaptations to conditions of their habitats?

Absolute and relative weight characteristics of 25 species of three-host exophilic ticks from 5 genera (Ixodes, Haemaphysalis, Dermacentor, Rhipicephalus, Hyalomma) have been compared. Ixodes and Haemaphysalis species differ from Hyalomma species by having lighter unfed females, heavier eggs and, hence, considerably smaller interstage compensatory growth. Ixodes and Haemaphysalis species considered in this paper are typical forest ticks while the Hyalomma species are typical ticks of open areas. Dermacentor and Rhipicephalus species by some absolute weight parameters (egg weight and unfed adult body weight, respectively) are similar to forest ticks but, according to the relative weight characteristics (weight ratios between unfed females and eggs, and between engorged and unfed nymphal ticks), they seem to be closer to the ticks of open areas. In Hyalomma, Dermacentor and Rhipicephalus species, the compensatory growth is mainly realized through a large weight increase during nymphal feeding. Several patterns of weight increase during feeding at each developmental stage are distinguished.

Interpretation of a Model for a DDT‐Treated Population of Ixodes persulcatus. II. Factors Contributing to Effectiveness of Acaricide Application

For effective control of pest or vector populations it is necessary to understand how the process of their suppression by control agents occurs. A model of the population suppression made on the basis of data on pest population biology can be helpful for this purpose. Such a model was proposed for Ixodes persulcatus, one of two main vectors of the tick-borne encephalitis (TJ3E) virus in the USSR.’ The model has shown how suppression of the whole population is achieved through suppression of certain parts (different stages) of the population (FIG. 1). Data presented in the first part of this paper2 make it possible to explain the process of suppression in more detail and to examine whether the model corresponds to the real process. Since Zxodespersulcatus is an organism specific to the USSR, almost all the literature on its biology and control is in Russian.

The influence of preprandial insemination on feeding and oviposition of Ixodes persulcatus females (Acari: Ixodidae) and some thoughts concerning mating strategies in ticks of the genus Ixodes

Prostriate ticks (subfamily Ixodinae, genus Ixodes) can copulate and the females can be inseminated before attachment to the host. In tests with Ixodes persulcatus females collected in the field and fed without males on the host, it was shown that this preprandial insemination is necessary and sufficient for successful engorgement and oviposition if female feeding took place in up to 1 month after collection. A 2-month period between preprandial insemination and female feeding was followed by a significant decrease in the proportion of normally engorged females and significant increase in egg mortality. If a small number of males were added to feeding females in this case, the number of normally engorged females increased but the egg mortality remained as high. Spermatophore destruction during the 2-month period is assumed to have a negative effect on the viability of eggs produced after additional (perprandial) insemination. Prostriate ticks are believed to be an intermediate group between argasid and metastriate ticks. Transition from nidicolous parasitism in argasid ticks to exophily (pasture parasitism) in metastriate ticks determines the change in mating strategy from off-host to on-host copulation. We review the available data concerning mating strategies in representatives of different subgenera of the genus Ixodes in the context of this evolutionary relationship.