Putative Vectors Research Articles

Ehrlichiosis in a Golf-Oriented Retirement Community

Ehrlichiosis due to Ehrlichia chaffeensis usually occurs sporadically or in small clusters, with an annual incidence estimated at 3 to 5 cases per 100,000 population in areas of endemic disease. The putative principal vector is the Lone Star tick (Amblyomma americanum). We investigated an outbreak of ehrlichiosis that occurred in June 1993 among members of a golf-oriented retirement community (community A) in Tennessee. The community is densely wooded and borders a wildlife-management area where deer are numerous. We conducted a case-control study, using medical-history reviews, serologic testing, and testing with the polymerase chain reaction for E. chaffeensis infection. We also surveyed a sample of 10 percent of the households in community A and in another golf-oriented community (community B) more than 20 miles (32 km) from the wildlife-management area. Survey participants completed a questionnaire and provided specimens for serologic testing. In both communities, searches for ticks were undertaken. Eleven cases of symptomatic ehrlichiosis were identified in the case-control study, 10 of which were in community A (attack rate, 330 per 100,000). Of 311 surveyed residents of community A, 12.5 percent had serologic evidence of past E. chaffeensis infection, as compared with 3.3 percent of 92 in community B (relative risk in community A as compared with community B, 3.9; 95 percent confidence interval, 1.2 to 12.2). The risk of infection was associated with tick bites, exposure to wildlife, golfing, and among golfers, retrieving lost golf balls from the rough. Persons who never used insect repellent were more likely to have had infection than persons who did. In community A, thousands of Lone Star ticks were found; in community B, only three ticks were found. The high rate of E. chaffeensis infection in community A resulted from its proximity to a wildlife reserve. When outdoor recreational activities are common and concentrations of ticks are high, outbreaks of arthropod-borne zoonoses can be anticipated.

Vectorial coding of movement: vision, proprioception, or both?

1. Subjects were asked to point toward visual targets without visual reafference from the moving hand in two conditions. In both conditions the pointing fingertip was viewed only before movement onset. 2. In one condition, the pointing fingertip was viewed through prisms that created a visual displacement without altering the view of the target. In another experimental condition, vision of the fingertip was not displaced. Comparison of these two conditions showed that virtually shifting finger position before movement through prisms induced a pointing bias in the direction opposite to the shift. The extent of this pointing bias was about one third of the prismatic shift applied to the fingertip. 3. Analysis of movement initial direction demonstrated that it was also less deviated than predicted from the prismatic shift. In addition, the reaction time and movement time of the reaching movement were increased. 4. This result is interpreted in the framework of the vectorial coding of reaching movement. Proprioception and vision provide two possible sources of information about initial hand position, i.e., the origin of the movement vector. The question remains as to how these two sources of information interact in specifying initial hand position when they are simultaneously available. 5. Our results are thus discussed with respect to a visual-to-visual movement vector hypothesis and a proprioceptive-to-visual vector hypothesis. It is argued that the origin of the putative movement vector is encoded by weighted fusion of the visual and the proprioceptive information about hand initial position.

Leishmaniasis in greater Athens, Greece. Entomological studies.

Greater Athens, the largest urban area in Greece, has a population of 3.1 million and is home for most of the human and canine cases of visceral leishmaniasis (VL) reported in Greece. Seven species of sandflies (Diptera: Psychodidae) were identified in light- and sticky-trap surveys in the area in 1993. Although none of the flies was found in wooded areas or scrub, flies were collected from quarries, corrals, wells, walls, houses and animal shelters. There were small 'island' populations in residential districts and moderate or large populations in the quarries and corrals in the foothills of the mountains bordering the area and in the hills near the city centre. Phlebotomus neglectus, the putative vector of VL in the area, was ubiquitous; it predominated in the quarries and was common in the sampled corrals and residential habitats. The distribution, abundance and seasonal activity of all seven species of sandflies are described and discussed.

Survey of the Anopheles maculatus complex (Diptera: Culicidae) in peninsular Malaysia by analysis of cuticular lipids.

Anopheles maculatus Theobald sensu lato is a species complex now consisting of eight sibling species; An. maculatus is still represented by two cytologically distinct forms; i.e., the widely distributed sensu strictu or B, and E from southern Thailand and adjacent areas in northern Malaysia. Cuticular lipid profiles in conjunction with principal component analysis was used to separate An. maculatus form E from sensu stricto form B in a preliminary survey of the An. maculatus complex at five locations spanning peninsular Malaysia. The relative rank orders, from the areas of the five gas chromatographic peaks used to determine lipid differences for specimens from peninsular Malaysia, matched well with those from cytogenetically identified colony specimens of An. maculatus forms B and E. The two-dimensional principal component pattern of specimens identified as form E was highly clumped, which indicated that very similar cuticular lipids were present within this putative malaria vector. Both forms coexisted in peninsular Malaysia, but form E may be dominant except in the south.

Detection of Borrelia burgdorferi in ticks by species-specific amplification of the flagellin gene.

We developed a polymerase chain reaction (PCR) that specifically amplifies a fragment of the flagellin gene (fla) of Borrelia burgdorferi, the causative agent of Lyme disease. This fla target, amplified with nested primers, was conserved among all 80 strains of B. burgdorferi tested. Strains examined included cultures from ticks, humans, and rodents from major B. burgdorferi-endemic regions of the United States and parts of Europe and Asia. Templates from B. hermsii, B. parkeri, B. turicatae, and B. coriaceae were not amplified, nor were eukaryotic DNAs from three tick genera. Several host DNAs potentially present in a tick blood meal also were not amplified. Approximately six B. burgdorferi per PCR reaction could be detected by ethidium bromide staining of amplified DNA. Colony-raised Ixodes dammini were used to evaluate the method. One infected nymph in a pool of 40 ticks was routinely detected. The specificity of the assay for detecting B. burgdorferi-infected ticks in pools was 94% (29 of 31). This protocol should prove useful for assessing infection rates in other putative arthropod vectors.

A study of sandfly species (Diptera: Psychodidae: Phlebotominae) in a focus of cutaneous leishmaniasis in the municipality of Baturité, Ceará, Brazil

In a study on putative vectors of cutaneous leishmaniasis in Baturité, Ceará State, Brazil, six sandfly species were identified: Lutzomyia longipalpis, L. wellcomei, L. peresi, L. whitmani, L. shannoni and L. migonei. In general L. whitmani and L. migonei were the predominant species. They were collected in periodomiciliary areas and were attracted by man and equines. L. whitmani was the most anthropophilic species. Studies using animals as bait showed that blood-feeding occurs throughout the night. Previously L. whitmani had been found infected with a Leishmania species of the braziliensis complex and L. migonei was infected with peripylarian flagellates. In combination these findings suggest that they may be responsible for periodomestic transmission of cutaneous leishmaniasis.

Trypanosomatid parasites of plants (phytomonas)

Trypanosomatids of the genus Phytomonas have been known as parasites of lactiferous plants since the beginning of the century and have been the subject of renewed attention in the past decade, as they are now recognized to be pathogenic in plants of economic interest. Nevertheless, information about these flagellates is still scanty. Until recently they had not been cultured, or studied biochemically or ultrastructurally. Phytophagous insects are their putative vectors but exactly which species are involved remains to be established. There are many unanswered questions about the taxonomic identification, pathogenecity and transmission of Phytomonas spp as well as about their natural hosts and reservoirs; this article by Erney Camargo, Pieter Kastelein and Isaac Roitman highlights some of them.

Transmission of murine typhus rickettsiae by Leptopsylla segnis (Siphonaptera: Leptopsyllidae).

Leptopsylla segnis fleas were found to be somewhat more effective in transmitting murine typhus infection to rats in the laboratory than had been the putative vector, Xenopsylla cheopis , as previously reported. The etiological agent, Rickettsia typhi (=R. mooseri) , appeared earlier in the feces of L. segnis than it had in X. cheopis , and the course of infection within the two species was essentially similar, although apparently proceeding at a somewhat accelerated rate in L. segnis . Because rickettsiae appeared in the foregut and proventriculus of L. segnis , it seems probable that this species can transmit the infection by bite, as has been recently shown for X. cheopis . Rickettsial development was appreciably more rapid under ambient conditions of 24°C than at 18°C. The role of L. segnis as a potential vector of murine typhus, at least among murid hosts, should be reconsidered.

Experimental Murine Typhus Infection in the Cat Flea, Ctenocephalides Felis (Siphonaptera: Pulicidae)1

During the feeding process, the cat flea, Ctenocephalides felis , acquires Rickettsia mooseri ( R. typhi ), the etiological agent of murine typhus, just as readily as does the putative vector, Xenopsylla cheopis . The course of infection within the species of fleas is similar. Following the logarithmic growth stage of R. mooseri during the first 9 days after the infectious feeding, the rickettsial content of the infected flea remained within 105–106 plaque-forming units/flea. In frozen sections of infected fleas prepared on the 9th day, the midgut epithelial cells were packed with rickettsiae. Rickettsia mooseri was noted within the lumen of the proventriculus and of the foregut in 20% of the cat fleas tested on the 15th–17th days, suggesting that transmission by bite may sometimes occur. Growth of the rickettsiae within the flea proceeded at a much more rapid rate when fleas were maintained under ambient conditions of 24 and 30 °C than when they were kept at 18 °C. The survival rates of infected fleas corresponded with those of uninfected controls throughout the 21 days of experimentation. The pattern and intensity of the laboratory infection of R. mooseri in C. felis , the broad host range and multiple feedings of this flea, and its past history as a suspected vector all suggest that C. felis may play a significant role in transmitting murine typhus infection to man and other mammals.

Transmission of Onchocerciasis by Local Black Flies on the Firestone Rubber Plantation, Harbel, Liberia

A quantitative description of the transmission dynamics of onchocerciasis on the Firestone Rubber Plantation, Harbel, Liberia is presented. The putative vector, Simulium yahense, comprised 98.5% of the flies examined. Diurnal vector-host contact was unimodal, expressing a distinct peak between 0800 and 1100 hours, particularly during the wet season. Perennial breeding occurs in the Firestone biotope, and is manifested by a mean annual daily landing rate of 75 flies per person per day. S. yahense is considered an efficient vector by nature of its anthropophily, moderate infective worm burden (4.3 infective larvae per infective fly) and its spatial and temporal ubiquitousness. Onchocerciasis transmission peaked during the dry season, when 73.5% of the annual transmission occurred. The mean annual transmission potential for the study area was estimated to be 1,425 infective larvae per person. The significance of onchocerciasis as a public health problem on the Plantation is discussed, and the potential for limiting transmission is considered.

Rickettsia Mooseri Infection in the Fleas Leptopsylla Segnis and Xenopsylla Cheopis

Detailed observations on the acquisition and propagation of experimental Rickettsia mooseri infection in two species of fleas are presented. Rickettsia mooseri infection became detectable by means of the direct fluorescent antibody test about 2 days earlier in Leptopsylla segnis than in the putative vector, Xenopsylla cheopis. By the 6th day after the infective feeding, the entire lining and the lumen of the midgut in L. segnis contained masses of rickettsiae and the agent was being passed in the feces of the flea, whereas in X. cheopis these events did not occur until the 8th day. Basic behavioral differences in the two species of flea may explain these discrepancies and also influence their ability to serve as vectors of murine typhus. As a semisessile flea and sustained feeder, L. segnis only rarely attaches to a second individual and thus has an opportunity to acquire a heavy dose of rickettsiae, if feeding on a rickettsemic host. X. cheopis, in contrast, feeds rapidly and intermittently, even on man, and generally leaves its host soon thereafter, later returning to the same or another host to feed again. While L. segnis may not be as efficient a vector as X. cheopis regarding the intramurine cycle or transmission to man of murine typhus, the dense accumulation of infective feces on certain sites on the fur of the host raises the possibility of air-borne infection to man or rodent. Infection with R. mooseri had no effect on the survival of X. cheopis and L. segnis. Furthermore, no visible cytopathological effect was found in the paraffin-embedded sections of infected fleas.(ABSTRACT TRUNCATED AT 250 WORDS)

Addendum

Phlebotominae sand flies have been involved as vectors of Leishmania. In Argentina, Nyssomyia neivai and Nyssomyia whitmani are involved as the main vectors of American Tegumentary Leishmaniasis (ATL). In the northeastern border of the country, an outbreak of ATL during 2004–2005 was associated with deforestation and subsequent settlement of farmers close to the edge of the forest. The aim of this work was to study the community composition of sand flies along time in farms located near primary and secondary forest in two environments: houses and pigsties. The association of abundance with temperature and precipitation was also evaluated for the most prevalent species. A total of 23,659 Phlebotominae belonging to the genera Nyssomyia, Migonemyia, Pintomyia, Evandromyia, Micropygomyia, Sciopemyia, Dampfomyia, Psathyromyia and Brumptomyia were captured. Ny. whitmani, which was the most abundant species, and Migonemyia migonei, which was the second most abundant species, were present throughout the year. Both species were positively associated with temperature, mostly up to 31–47 days, and with precipitation at 31 days before the sampling day. The abundance was higher in pigsties than in houses, but the time pattern was positively associated between both environments. These results confirm that Ny. whitmani is the dominant species in the study area and its presence throughout the year indicates a potential long period of ATL transmission. The presence of Mg. migonei as the second species in abundance is relevant, because it has been described as a secondary vector of the parasites of ATL and a putative vector of the agent of American Visceral Leishmaniasis. We discuss the role of the pigsty as the environment that attract more sandflies, taking into account the number of sand flies captured there, the distance from the home, and the association of sand fly abundance with each of the two environments.