Monitoring of malaria vectors at the China-Myanmar border while approaching malaria elimination.

BACKGROUND: Tengchong County was one of the counties located at the China-Myanmar border with high malaria incidence in the previous decades. As the pilot county for malaria elimination at the border area, Tengchong County is aiming to be the first county to achieve malaria elimination goal. A cross-sectional entomological survey was carried out to evaluate the feasibility of elimination approach and assess the receptivity of malaria reintroduction. METHODS: Light traps associated with live baits were used to investigate the abundance of adult mosquitoes in nine villages in Tengchong County. Light traps were set to collect adult mosquitoes in both human houses and cowsheds from dusk till dawn in each site. RESULTS: A total of 4948 adult Anopheles mosquitoes were collected from May to December in two villages. Of the mosquitoes were captured, 24.2% were in human houses and 75.8% in cowsheds. The peak of abundance occurred in July for An. sinensis and in September-October for An. minimus (s.l.) Ten Anopheles species were collected, the most prevalent being An. sinensis (50.3%), An. peditaeniatus (31.6%) and An. minimus (s.l.) (15.8%), contributing to 97.6% of the sample. Potential breeding sites were also investigated and a total of 407 larvae were collected, with An. sinensis (50.1%) and An. minimus (s.l.) (46.2%) as predominant species. Ponds and rice fields were the two preferred breeding sites for Anopheles mosquitoes; however, the difference between the number of adults and larvae captured suggest other breeding sites might exist. Both An. sinensis and An. minimus (s.l.) were found zoophilic with human blood index as 0.21 and 0.26, respectively. No Plasmodium positive Anopheles specimens were found by PCR among 4,000 trapped mosquitoes. CONCLUSIONS: Although no indigenous malaria cases have been reported in Tengchong County since 2013, there is still a risk from the presence of vectors in the context of human population movements from neighboring malaria endemic areas. The presence of An. sinensis, associated to rice fields, is particularly worrying. Sustained entomological surveillance is strongly suggested even after malaria elimination certification.

[Screening Radius of Active Case Detection and the Malaria Parasite Rate of Carriers in China-Myanmar Border].

OBJECTIVE: To explore the effective screening radii of active case detection of the 1-3-7 surveillance and response strategy, and investigate the malaria parasite rate of carriers in China-Myanmar border. METHODS: Three villages with indigenous malaria cases in Yingjiang County of Yunan Province were selected as study sites. The persons lived around the indigenous cases (index case) within the radius of 100 m, 300 m, 500 m, and 1 km were screened by microscopy and nested PCR. Parasite rate of asymptomatic carriers at different radii were calculated. RESULTS: Among 278 blood samples, the parasite rate of asymptomatic carriers was 1.1% (3/278) and 2.2% (6/278) using microscopy and nested PCR, respectively. Based on the results of nested PCR, all the asymptomatic carriers could be detected within a 300 m radius around the index case, and with the highest proportion (66.7%) in the radius of 101-300 m. CONCLUSION: The asymptomatic carriers of malaria parasites in the China-Myanmar border area can be effectively detected within a 300 m screening radius of index case by using nested PCR.

[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.

Malaria transmission potential in the Three Gorges Reservoir of the Yangtze River, China.

OBJECTIVE: To define and evaluate the malaria transmission potential in the Yangtze River, following construction of the Three Gorges Reservoir. METHODS: Six villages, namely, Kaixian, Fengjie, Wanzhou, Fuling, Yubei, and Zigui were selected for investigating the malaria transmission potential in the reservoir. Transmission potential was estimated by mathematical modeling and evaluation of the local malaria situation. Factors that influenced the transmission potential were analyzed using Poisson regression analysis in combination with Grey Systematic Theory (based on evaluation by the Delphi method). RESULTS: Indirect fluorescent antibody data and the incidence of malaria in the local population were consistent with the malaria transmission potential calculated for the area. Multivariate Poisson regression analysis showed a statistically significant association between the riparian zone and the man-biting rate. CONCLUSION: The risk of a malaria epidemic can be forecasted using the malaria transmission potential parameters investigated here which was closely correlated with the riparian zone.

[Stabilities of two kinds of Plasmodium antigen substrate slides under different storage temperatures and time].

OBJECTIVE: To observe and compare the inspection effects of antigen substrate slides of Plasmodium cynomolgi (P. c) and Plasmodium falciparum (P. f) on the malaria antibody titer under different storage temperatures and time. METHODS: The densities of Plasmodium of P. c and P. f antigen slides were counted through a microscope, and the average numbers of Plasmodium in each field of vision were calculated. The pooled serum of patients with tertian malaria and falciparum malaria were treated as antibody serum, and the dilutions were from 1:5 to 1:1 280. The two kinds of antibody slides were placed under the temperature of 4-6, 25-27, 33-35 degrees C, and two slides of each kind were selected at Day 3, 5, 7, 10 post-storage to detect the end point antibody titer of malaria by the indirect fluorescent antibody test. Meanwhile, the P. c and P. f antigen slides storing under -20 degrees C for 1 year and 2 years were placed under the aforementioned 3 temperature conditions for 3 d, and the changes of the antibody titers were compared. RESULTS: The densities of Plasmodium in blood cells of P. c and P. f antigen slides were 2.00 x 10(5)/microl and 1.89x 10(5)/microl, respectively, and the average numbers of Plasmodium in each field of vision were 157 +/- 13 and 142 +/- 9, respectively. The end point titers of antibody of P. c and P. f antigen slides placed under the temperatures of 4-6, 25-27, 33-35 degrees C were all on a downward trend after storing for 5 d. The average antibody titers of the two kinds of slides under temperature of 4-6 degrees C and above were 1:440 and 1:80, respectively, and there was a significantly statistic difference between them(t = 1.940, P < 0.05). When P. c and P. f antigen slides storing under -20 degrees C for 1 year were placed under 4-6 degrees C for 3 d, the end point antibody titers were both 1:640, while for those storing under -20 degrees C for 2 years, the end point antibody titers were 1:320 and 1:160, respectively, both the differences were statistically significant (t(P. c) =11.362, P(P. c) < 0.01; t(P. f) = 38.845, P(P. f) < 0.001). CONCLUSION: The end point antibody titers for malaria detection of P. c and P. f antigen slides decrease gradually with the raise of temperature and the prolonging of time for storage.

[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.

[Factors affecting malaria outbreak in Congjiang county of Guizhou Province].

OBJECTIVE: To make a field investigation on the affecting factors of malaria outbreak in a village of Congjiang County, Guizhou Province. METHODS: The investigation was made in August, 2006. Filter paper dry blood samples were taken for indirect fluorescent antibody test (IFAT) from all the 495 residents above 1 year-old in the village where an outbreak of malaria was reported. Questionnairing was conducted in 423 villagers over 10 years-old, covering malaria history in the past 2 years, knowledge on malaria and its control, use of mosquito nets, and out-door sleeping habit. Data on febrile outpatients were collected from the records of the township health center for analyzing the compliance of the patients in seeking medical services. Mosquito collecting by human-bait before mid-night, and in mosquito nets and cattle pens in early morning was performed for mosquito composition and man-biting rate. RESULTS: Re-examination of the 42 positive blood smears confirmed 12 positives of P. vivax infection. The malaria incidence in 18 d was 2.1%, including 4 cases clinically diagnosed. The antibody positive rate of IFAT in the population was 8.7% (43/495) with a positive GMRT of 20.6, overall GMRT of 10.6; the IFAT positive rate in the age group of under 5 was 7.5% (3/40) with a GMRT of 25.1. The rate of seeking medical advice among febrile patients was 81.3% (118/145), 78.8% (93/118) of which being in the village clinic. The average time of going to a doctor after fever was 3.9 days, 37.4% (195/521) and 3.3% (17/521) were in 4-6 days and over 10 days respectively, with the longest 26 days. The average knowledge rate on malaria was 25.5% (108/423), with 17.1%, 29.2% and 40.0% in the groups of illiteracy, primary school and high school education respectively. A statistical significance was found between primary school/high school education and the illiteracy (P<0.01). The average rate of using mosquito nets was 31.0% (131/423), out-door sleeping rate was40.7% (172/423). The radical cure rate in 2004 and 2005 was 68.2% (15/22) and 48.3% (14/29) respectively. In addition to Anopheles sinensis, An. anthropophagus and An. minimus also existed in rooms and nets with a man-biting rate of 0.0566 and 0.0755 respectively. CONCLUSIONS: Three species of anopheline mosquitoes are the important transmitting vectors. Poor self-protection, outdoor sleeping habit, delayed examination and treatment, and irregular chemotherapy among the residents are the main factors resulting malaria outbreak.

[Morphology and habits of An. anthropophagus and its role in malaria transmission in Hengqin Island of Zhuhai City].

OBJECTIVE: To study the morphology and ecological habits of An. anthropophagus and its role in malaria transmission in Hengqin Island of Zhuhai City, Guangdong Province. METHODS: Mosquitoes were captured through overnight/semi-overnight trapping with human and cattle baits as well as lamp-trapping. The specimens were morphologically identified through describing the adult mosquitoes, eggs and pupae. The relevant parameters were collected to calculate the vectorial capacity of both An. anthropophagus and An. sinensis. RESULTS: There is no morphological difference between the isolate of An. aothropophagus from Hengqin Island and that from Jiangsu Province. Its human blood preference ratio and human blood index was 0.94 and 0.75 respectively, and the vectorial capacity of An. anthropophagus was 7.36 times higher than that of An.sinensis (5.1914/0.7052). CONCLUSION: The isolate of An. anthropophagus from Hengqin Island belongs same species to that from the mainland, which prefers to human blood and shows higher malaria transmission potential.