[Investigation on blood-sucking habit of Anopheles (Diptera:Culicidae) using multiplex polymerase chain reaction in malaria-endemic area of Chayu County, Tibet].

OBJECTIVE: To determine the blood-sucking habit of anopheline by mosquitoes bloodmeal identification in malaria endemic area Chayu County, Tibet Autonomous Region. METHODS: Three villages with different bio-environments were selected as the investigation spots. Light traps were set up outdoor and in livestock sheds from sunset (20:00) to sunrise (8:00) in 3-4 consecutive nights to collect mosquitoes. The trapped anophelines were counted and identified according to morphological criteria and multiple PCR method. A PCR-based methodology according to the mtDNA-cytb variations was used in different mammal hosts to identify bloodmeal sources in engorged mosquitoes. The human blood index (HBI) was assessed to determine the range of hosts. RESULTS: Among 1 442 anopheline mosquitoes collected by 108 light traps on 13 nights. 1436 (99.6%) belonged to Anopheles maculatus complex, with 85.5% An. pseudo-willmori and 14.5% An. willmori. Positive bloodmeal identification was found from 168 (83%) of 202 field-collected engorged mosquitoes. The crude HBI of An. pseudowillmori and An. willmori were 035 and 0.29, respectively. CONCLUSION: An. pseudowillmori and An willmori are both zoophilic and anthropophilic, and An. pseudowillmori shows a higher HBI.

[Investigation on Anopheles species and their composition in villages at different altitudes of Motuo County, Tibet Autonomous Region].

OBJECTIVE: To study the anopheline species and composition in villages at different altitudes, Muotuo County. METHODS: Six villages with different altitudes were selected as the investigation spots, i.e. Gande, Zhucun, Damu, Motuo, Didong and Beibeng with an altitude 1 966 m, 1 510 m, 1 408 m, 1 178 m, 853 m and 831 m, respectively. Human-baited net traps, cow-baited traps and light traps were set up to collect adult mosquitoes. The trapped mosquitoes were counted and identified according to morphological criteria. Following the classification, the mosquitoes were killed by chloroform and dried on silica-gel, and transported to the laboratory where they were stored at -20 degrees C. Species of Anopheles maculatus complex were identified with multiple PCR method. RESULTS: 5 410 anopheline mosquitoes were collected. Two mosquitoes were captured in high altitude village, one was Anopheles gigas bailieyi, while the other was damaged and unable to identify. There were 541 (36.9%) An. pseudowillmori, 906 An. willmori (61.7%) and 21 An. peditaeniatus (1.4%) collected in semi-high altitude villages; 260 (76.3%) An. pseudowillmori, 2 An. willmori (0.6%) and 79 An. peditaeniatus (23.2%) trapped in middle altitude village; and 3265 (90.7%) An. pseudowillmori, 19 An. willmore (0.5%) and 315 An. peditaeniatus (8.8%) trapped in low altitude villages. CONCLUSION: An. pseudowillmori, An. willmore and An. peditaeniatus make the main anopheline composition. The proportion of An. willmore is higher than An. pseudowillmori in semi-high altitude villages, while An. pseudowillmori take the absolute predominance in middle and low altitude villages.

[Investigation on malaria transmission vectors in Motuo County, Tibet Autonomous Region].

OBJECTIVE: To investigate the malaria transmission vectors in Motuo County of Linzhi Prefecture, Tibet. METHODS: Three natural villages with higher malaria incidence rate in Motuo County were selected for the study in July and August, 2007. The anopheline mosquitoes were collected by overnight/semi-overnight trapping indoor and outdoor with human and cattle baits, overnight trapping with ovitrap lights in human dwellings and cowsheds, and by searching in human dwellings in the early morning. The mosquitoes collected were identified morphologically, and the group proportion, density, man-biting rate, blood preference, habits and multiparous ratios were observed. Mosquito larvae breeding place was surveyed, and species of the larvae were identified. RESULTS: A total of 5345 anopheline mosquitoes were captured with 94.71% (5 062/5 345) of An. pseudowillmori, 2.39% (128/5 345) of An. willmori and 2.90% (155/5 345) of An. peditaeniatus. The average density of An. pseudowillmori observed through semi-overnight trapping was 17/per person indoor and 105/per person outdoor. The average man-biting rate of An. pseudowillmori through overnight trapping was 15.80/per person (79/5) indoor and 326.22/per person (1468/4.5) outdoor. The ratio of blood preference to human and cattle through overnight trapping outdoor were 30.51% (714/2340) and 69.49% (1626/2340), and 32.02% (57/178) and 67.98% (121/178) through overnight trapping with ovitrap lights respectively. It suggested that An. pseudowillmori feeding both of the human and cattle blood but preferred to cattle blood. Totally 7 An. pseudowillmori mosquitoes were found in the human dwellings in the early morning, and none of them has digested the engorged blood. The Anopheles larvae were only found in the rice field where 106 larvae were collected, including 62 An. pseudowillmori larvae, An. willmori larvae, and 44 An. peditaeniatus larvae. CONCLUSION: An. pseudowillmori seems qualified as the vector biological perspectives for the local malaria transmission.

[Epidemiological survey on malaria situation in Motuo County of Tibet, China].

OBJECTIVE: To make an epidemiological investigation on malaria in Motuo County, Linzhi Prefecture of Tibet. METHODS: In July of the year 2006, the following activities were conducted in 2 selected villages from each of the three townships, i.e., Motuo, Dexing and Beibeng: malaria history survey among inhabitants in recent 2 years; collection of blood samples of inhabitants for examining malaria parasites, IFAT and detecting G6PD, respectively; mosquito collection in human dwellings and cattle shelters at night and various resting sites at day-time; mosquito collection by outdoor human baiting capture; classification and composition calculation of mosquito species and man biting rates; ELISA for detecting sporozoite infection of Anopheles. RESULTS: The mean rate of two-year malaria history was 8.98% (118/1314) and the parasite rate was 3.13% (38/1216, all P. vivax) in the inhabitants. The parasite positive rate among the feverish patients was 7.14% (3/42). IFAT revealed a malaria antibody rate of 40.24% (472/1173). The G6PD deficiency rate was 1.74% (21/1208). Five hundred and thirteen anopheline mosquitoes were caught. They were An. maculatus (474) which occupied 92.4% (474/513), An. peditaeniatus (35), An. kochi (3) and An. sinensis (1). The mean indoor density of An. maculatus was 4.75/night in human houses, and 69.5/night in cattle shelters. The outdoor human biting rate was 22.75/half-night/person, and the sporozoite rate of An. maculatus in anopheline saliva glands was 0 by ELISA. CONCLUSION: Motuo County is an endemic area of vivax malaria with An. maculatus as the potential vector.

[Ecological behavior comparison between Anopheles pseudowillmori and A. willmori in villages with malaria outbreaks in Motuo County, Tibet Autonomous Region].

OBJECTIVE: To understand the ecological behaviors of Anopheles pseudowillmori and A. willmori in medium or high altitude areas of Motuo County, Tibet Autonomous Region, and their transmission potential for malaria. METHODS: The methods of human net traps, cow baited trap, house baited trap, pig baited trap and CDC light traps were adopted for investigating the mosquito density, biting activity at night and in or out door preference of biting. All mosquitoes morphologically identified as A. maculatus group were labeled in accordance with the capture time, place and method, and PCR were used to identify the species. The resting habits were investigated with the morning capture and daytime collecting methods, and the larvae collected in different wa- ter bodies were reared to adults to study the breeding place. RESULTS: A total of 1,053 A. maculatus group were collected, and of which, 331 (31.43%) were identified as A. pseudowillmori, and 722 (68.57%) as A. willmori. The number of A. willmori were higher than A. pseudowillmori in both outer and inner doors (P < 0.01, P < 0.05) , while no statistically significant difference was found of the constituent ratio of the anopheles between outer and inner doors. The multiparous ratios of A. pseudowillmori and A. willmori were 65.90% and 69.86%, respectively, (P > 0.05). The A. pseudowillmori preferred to biting outer doors (P < 0.05), while A. willmori preferred both outer and inner doors (P > 0.05). Both mosquitoes had one biting activity peak in the night, and the biting activity peak of A. willmori was from 21 to 22 o'clock, while the peak of A. pseudowillmori was from 24 to next morning 1 o' clock. CONCLUSION: In the Anopheles, the constituent ratio and density of A. willmori are higher than those of A. pseudowillmori in semi-high altitudes area of Motuo County, Tibet, and there are obvious differences of ecological behaviors between A. willmori and A. pseudowillmori, and A. willmori has the more capacity of transmitting malaria than A. pseudowillmori.