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Animals↗

Pyrethroid resistance/susceptibility and differential urban/rural distribution of Anopheles arabiensis and An. gambiae s.s. malaria vectors in Nigeria and Ghana.

Resistance to pyrethroid insecticides and DDT caused by the kdr gene in the malaria vector Anopheles gambiae Giles s.s. (Diptera: Culicidae) has been reported in several West African countries. To test for pyrethroid resistance in two more countries, we sampled populations of the An. gambiae complex from south-western Ghana and from urban and rural localities in Ogun State, south-west Nigeria. Adult mosquitoes, reared from field-collected larvae, were exposed to the WHO-recommended discriminating dosage of exposure for 1 h to DDT 4%, deltamethrin 0.05% or permethrin 0.75% and mortality was recorded 24 h post-exposure. Susceptibility of An. gambiae s.l. to DDT was 94-100% in Ghana and 72-100% in Nigeria, indicating low levels of DDT resistance. Deltamethrin gave the highest mortality rates: 97-100% in Ghana, 95-100% in Nigeria. Ghanaian samples of An. gambiae s.l. were fully susceptible to permethrin, whereas some resistance to permethrin was detected at 4/5 Nigerian localities (percentage mortalities 75, 82, 88, 90 and 100%), with survivors including both An. arabiensis Patton and An. gambiae s.s. identified by PCR assay. Even so, the mean knockdown time was not significantly different from a susceptible reference strain, indicating absence or low frequency of kdr-type resistance. Such low levels of pyrethroid resistance are unlikely to impair the effectiveness of pyrethroid-impregnated bednets against malaria transmission. Among Nigerian samples of An. gambiae s.l., the majority from two urban localities were identified as An. arabiensis, whereas the majority from rural localities were An. gambiae s.s. These findings are consistent with those of M. Coluzzi et al. (1979). Differences of ecological distribution between molecular forms of An. gambiae s.s. were also found, with rural samples almost exclusively of the S-form, whereas the M-form predominated in urban samples. It is suggested that 'urban island' populations of An. arabiensis and of An. gambiae s.s. M-form in the rainforest belt of West Africa might be appropriate targets for elimination of these malaria vectors by the sterile insect technique.

Animals↗

Molecular genetic manipulation of mosquito vectors.

Despite their central role in disease transmission, relatively little is known of the molecular biology of arthropod vectors. Modern molecular approaches will undoubtedly provide considerable information about gene regulation and expression in vectors and consequently a much better understanding of the biology and molecular biology of vectors. Such knowledge is essential for developing effective control strategies for vector-borne diseases. In this review, we focus upon techniques and approaches used at the Arthropod-Borne and Infectious Diseases Laboratory (AIDL) at Colorado State University to bioengineer mosquitoes with reduced vector competence. We have developed technologies and procedures that allow genetic manipulation of mosquitoes, including RNA and DNA virus gene-delivery vehicles and efficacious antiviral constructs, which will facilitate the development of pathogen-resistant, transformed mosquitoes. Many of the approaches, constructs, and technologies developed at AIDL will be applicable to molecular manipulation of other arthropod genomes.

Animals↗

Chagas' disease in the Amazon basin: V. Periurban palms as habitats of Rhodnius robustus and Rhodnius pictipes--triatomine vectors of Chagas' disease.

Trypanosoma cruzi infected Rhodnius robustus and/or Rhodnius pictipes were commonly found, in large numbers, in the Brazilian Amazonian palms Maximiliana regia ("inajá"), Acrocomia sclerocarpa ("mucajá") and Orbignya speciosa ("babaçu"). The common opossum, Didelphis marsupialis, was the animal most frequently associated with triatomine infested palms. R. pictipes, frequently light-attracted into houses from palm trees, was the probable source of an acute case of Chagas' disease in the vicinity of Belém. It is considered that triatomine infested palms are likely to cause some cases of acute Chagas' disease in the States of Amazonas and Rondônia. Possible control methods are suggested.

Animals↗

Leishmanial infection: analysis of its first steps. A review.

The first steps in leishmaniasis are critical in determining the evolution of the disease. Major advances have recently been done in understanding this crucial moment. Fundamental research in parasite-vector interaction, parasite biology, insect saliva, and vertebrate host response have shed new light and uncovered a most fascinating and complex moment in leishmaniasis. We review here some of these aspects and we try to connect them in a logical framework.

Animals↗

Anaplasmosis.

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Anaplasmosis↗

[Detection of dengue virus genome RNA in some kinds of animals caught from dengue fever endemic areas in Hainan Island with reverse transcription-polymerase chain reaction].

Detection of dengue virus genome RNA in brain of bats caught from dengue fever endemic areas in Hainan Island were carried out with reverse transcription-polymerase chain reaction(RT-PCR). Positive result was demonstrated in 20 of 35 bats tested, with a positive rate of 57.14%; RT-PCR was applied for the detection of dengue virus genome RNA in sera of bats caught from the endemic areas in Hainan Island, 3(16.66%) of 18 sera were positive. Dengue virus genome RNA in female Aedes aegypti captured from dengue fever endemic areas in Hainan Island was detected by using RT-PCR, 1(33.33%) of 3 lots was positive. Similar examinations on bat brains and mosquitoes captured from non-endemic areas were all negative. In addition, monoclonal IgG antibodies against types 1-4 dengue viruses were added onto brain imprints of bats captured from endemic areas of dengue fever in Hainan Island, 16(80.00%) of 20 showed positive results for type 2 dengue virus antigen by direct immunofluorescent assay. The antibodies to various types of dengue virus were coincided to that of dengue virus genome RNA. The above results proved that bat is the reservoir of dengue virus, and this provides an important clue for the effective control of dengue fever epidemics in endemic areas.

Aedes↗