Genetic compatibility between Anopheles lesteri from Korea and Anopheles paraliae from Thailand

To assess differentiation and relationships between Anopheles lesteri and Anopheles paraliae we established three and five iso-female lines of An. lesteri from Korea and An. paraliae from Thailand, respectively. These isolines were used to investigate the genetic relationships between the two taxa by crossing experiments and by comparing DNA sequences of ribosomal DNA second internal transcribed spacer (ITS2) and mitochondrial DNA cytochrome c oxidase subunit I (COI) and subunit II (COII). Results of reciprocal and F1-hybrid crosses between An. lesteri and An. paraliae indicated that they were compatible genetically producing viable progenies and complete synaptic salivary gland polytene chromosomes without inversion loops in all chromosome arms. The pairwise genetic distances of ITS2, COI and COII between these morphological species were 0.040, 0.007-0.017 and 0.008-0.011, respectively. The specific species status of An. paraliae in Thailand and/or other parts of the continent are discussed.

Susceptibility of Anopheles campestris-like and Anopheles barbirostris species complexes to Plasmodium falciparum and Plasmodium vivax in Thailand

Nine colonies of five sibling species members of Anopheles barbirostris complexes were experimentally infected with Plasmodium falciparum and Plasmodium vivax. They were then dissected eight and 14 days after feeding for oocyst and sporozoite rates, respectively, and compared with Anopheles cracens. The results revealed that Anopheles campestris-like Forms E (Chiang Mai) and F (Udon Thani) as well as An. barbirostris species A3 and A4 were non-potential vectors for P. falciparum because 0 percent oocyst rates were obtained, in comparison to the 86.67-100 percent oocyst rates recovered from An. cracens. Likewise, An. campestris-like Forms E (Sa Kaeo) and F (Ayuttaya), as well as An. barbirostris species A4, were non-potential vectors for P. vivax because 0 percent sporozoite rates were obtained, in comparison to the 85.71-92.31 percent sporozoite rates recovered from An. cracens. An. barbirostris species A1, A2 and A3 were low potential vectors for P. vivax because 9.09 percent, 6.67 percent and 11.76 percent sporozoite rates were obtained, respectively, in comparison to the 85.71-92.31 percent sporozoite rates recovered from An. cracens. An. campestris-like Forms B and E (Chiang Mai) were high-potential vectors for P. vivax because 66.67 percent and 64.29 percent sporozoite rates were obtained, respectively, in comparison to 90 percent sporozoite rates recovered from An. cracens.

Karyotypic variation and geographic distribution of Anopheles campestris-like (Diptera: Culicidae) in Thailand

Seventy-one isolines of Anopheles campestris-like were established from wild-caught females collected from human-biting and animal-biting traps at 12 locations in Thailand. All isolines had an average branch summation of seta 2-VI pupal skins ranging from 20.3-30.0 branches, which is in the range of An. campestris (17-58 branches). They showed three different karyotypes based on the amount of extra heterochromatin in the sex chromosomes, namely Forms B (X2, Y2), E (X1, X2, X3, Y5) and a new karyotypic Form F (X2, X3, Y6). Form B has been found only in Chaing Mai and Kamphaeng Phet populations, while Forms E and F are widely distributed throughout the species range. Genetic crosses between the 12 isolines, which were arbitrarily selected as representatives of An. campestris-like Forms B, E and F, revealed genetic compatibility that provided viable progeny through F2 generations, suggesting a conspecific nature of these karyotypic forms. These results are supported by the very low intraspecies variation (genetic distance < 0.005) of ITS2, COI and COII from genomic DNA of the three karyotypic forms.

A survey of dengue viral infection in Aedes aegypti and Aedes albopictus from re-epidemic areas in the north of Thailand using nucleic acid sequence based amplification assay.

Immature stages of Aedes aegypti and Ae. albopictus were collected from 17 dengue re-epidemic areas in Chiang Mai and Lampang Provinces, in the north of Thailand. They were reared to adults and tested for dengue viral RNA by a nucleic acid sequence based amplification assay (NASBA). Of a total of 9,825 Ae. aegypti and 150 Ae. albopictus examined, none of them were found positive for the virus, suggesting that transovarial transmission may be very low in the vector populations and may not play a significant role in the epidemiology of dengue infection in Thailand.

Knowledge and use of preventive measures against malaria in endemic and non-endemic villages in northern Thailand.

The objective of this study was to determine the frequency and determinants of knowledge of malaria in four sites in northern Thailand, and to compare the use of prevention measures between people with and without a knowledge of malaria. An epidemiological survey was conducted in January 2002 among 857 persons living in four sites in northern Thailand. Of the 857 persons, 53% had a knowledge of malaria, ranging from 38% and 51% in non-endemic to 76% and 77% in endemic sites. Headache (89%), shivering (83%) and fever (79%) were the most frequently mentioned symptoms. Younger persons had more knowledge of malaria than older persons; adjusted Odds Ratio (aOR): 3.91 [95% confidence interval (CI): 2.32-6.56] for the 15-29 age group compared to persons 60 years and older. In comparison to men, knowledge of malaria was significantly lower among women (aOR: 2.00, 95%-CI: 1.47-2.70). Persons with knowledge reported a significantly higher use of prevention measures than persons without knowledge of malaria.

Susceptibility of two karyotypic forms of Anopheles aconitus (Diptera: Culicidae) to Plasmodium falciparum and P. vivax

Quatro colônias desenvolvidas em laboratório, de duas formas cariotípicas de Anopheles aconitus i.e. forma B (cepa Chiang Mai e Phet Buri) e C (Cepa Chiang Mai e Mae Hong Son), foram infectadas experimentalmente com Plasmodium falciparum e P. vivax usando técnica de alimentação com membrana artificial e dissecados oito e 12 dias após alimentação da média de oocistos e esporozoitos, respectivamente. Os resultados revelaram que An. aconitus formas B e C foram suscetíveis ao P. falciparum e P. vivax isto é, forma B (cepa Chiang Mai e Phet Buri/P. falciparum e P. vivax) e forma C (cepa Chiang Mai e Mae Hong Son/P. vivax). Análises estatísticas comparativas das taxas de oocistos, número médio de oocistos por intestino médio infectado e taxas de esporozoitos entre todas as cepas de An. aconitus formas B e C ao grupo interno de vetores controles, An. minimus A e C, não exibiram nenhuma diferença significante, confirmando o alto potencial vetor das duas espécies de Plamodium. Os cristais semelhantes a esporozoitos encontrados no lobo médio das glândulas salivares que poderiam ser um fator enganoso na identificação de esporozoitos verdadeiros nas glândulas salivares foram encontrados em ambos An. aconitus formas B e C.

The specific status of Anopheles minimus s.l. collected from Taiwan.

At least three members (species A, C, and E) of the Anopheles minimus complex have been described in the Orient. This study investigated the specific status of An. minimus collected in the southern part of Taiwan by crossing experiments with species A from Thailand and species E from Japan. Crosses between Taiwan An. minimus and species A revealed genetic compatibilities. Post-zygotic isolation was observed in crosses between Taiwan An. minimus and species E. Hybrid progeny were only obtained from Taiwan female X species E male. F2 hybrid progeny were not obtained, since the hybrid males were sterile or almost sterile, with atrophied testes or abnormal spermatozoa. The hybrid females backcrossed with either Taiwan F1 progeny and species E males, and laid eggs with lower fertility and viability. This study supports previous published data regarding the analysis of the D3 region of the 28S gene of ribosomal DNA that An. minimus species A is indigenous to Taiwan. Whether other members of the An. minimus complex exist in Taiwan is not conclusive and needs more study.

Comparative morphometry and morphology of Anopheles aconitus Form B and C eggs under scanning electron microscope

Estudos comparativos morfométricos e morfológicos de ovos à microscopia eletrônica de varredura (SEM) foram efetuados nas três linhagens de duas formas cariotípicas de Anopheles aconitus, isto é, Forma B (linhagens Chiang Mai e Phet Buri) e Forma C (linhagens Chiang Mai e Mae Hong Son). Exame morfométrico revelou a variação intraespecífica com respeito à largura de superfície [36,77 ± 2,30 µm (Forma C: linhagem Chiang Mai) = 38,49 ± 2,78 µm (Forma B: linhagem Chiang Mai) = 39,06 ± 2,37 µm (Forma B: linhagem Phet Buri) > 32,40 ± 3,52 µm (Forma C: linhagem Mae Hong Son)] e número de tubérculos posteriores sobre a superfície livre [2,40 ± 0,52 (Forma B: linhagem Phet Buri) = 2,70 ± 0,82 (Forma B: linhagem Chiang Mai) < 3,10 ± 0,32 (Forma C: linhagem Chiang Mai) = 3,20 ± 0,42 (Forma C: linhagem Mae Hong Son)] embora a topografia de superfície dos ovos entre as três linhagens de duas formas cariotípicas tenham sido morfologicamente semelhantes.

Insecticide susceptibility tests of Anopheles minimus s.l., Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus in northern Thailand.

The susceptibility of Anopheles minimus s.l., Aedes aegypti, Ae. albopictus, and Culex quinquefasciatus to insecticide in northern Thailand was monitored by using the WHO standard susceptibility test. One- to two-day old female mosquitos, which were reared from wild caught females or immature stages, were exposed to discriminating dosages of insecticides for recommended exposure periods, and the 24-hour mortality recorded. The results revealed that, in general, An. minimus s.l. was still susceptible to DDT and permethrin, except in some areas where a slight increase in tolerance to DDT was observed. Ae. aegypti and Ae. albopictus were both highly resistant to DDT, but in some areas the former was also resistant to permethrin and deltamethrin. Cx. quinquefasciatus was resistant to DDT and etofenprox, with a slight increase in tolerance to permethrin, deltamethrin, malathion and fenitrothion. No resistance to lambda-cyhalothrin was detected in any of the species studied.

Trypsin and aminopeptidase activities in blood-fed females Anopheles dirus (Diptera: Culicidae) of differing susceptibility to Plasmodium yoelii nigeriensis.

Midgut proteolytic enzymes contribute to the success or failure of Plasmodium infection of the mosquito. The present study investigated trypsin and aminopeptidase activities in the midgut of two strains of Anopheles dirus selected for susceptibility and refractoriness to Plasmodium yoelii nigeriensis. At intervals of 6 hours following a bloodmeal, the midguts of fully engorged female mosquitos were dissected, homogenized, and assayed for enzyme activity. No differences trypsin activity (nmole/min) were observed between the two strains throughout the course of blood digestion. By contrast, the aminopeptidase activity measured at 0 to 18 hours post-feeding was the same for the two strains, but at 24, 30 and 36 hours significantly less activity was observed in the refractory females. The results suggest neither trypsin nor aminopeptidase plays a role in the limitation of parasite development.

Intraspecific hybridization of Anopheles minimus (Diptera: Culicidae) species A and C in Thailand.

Hybridization tests of laboratory-raised, isolines of Anopheles minimus, species A and C were conducted by induced copulation. The three isolines were established based on three morphological variants of wild-caught, fully engorged females and two distinct types of metaphase chromosomes. They were An. minimus species A: V form (X1,Y1), M form (X2,Y1); species C: P form (X3,Y2). The results of reciprocal and back crosses indicated that the two morphologically variant forms of species A were genetically compatible, providing viable progeny and completely synaptic salivary gland polytene chromosomes, whereas they were genetically incompatible with species C and/or the P form. Hybrid progeny was only obtained from both forms of species A females x species C males, but asynaptic salivary gland polytene chromosomes on 3L and partial development of ovarian follicles in females were seen. Back crosses of F1 hybrid males with parental species A females provided viable progeny, while back crosses of F1 hybrid females with parental species C males provided progeny of low viability and adult males with abnormal spermatozoa, suggesting the partial reproductive isolation of An. minimus species A and C.