Extensive Resistance of Anopheles sinensis to Insecticides in Malaria-Endemic Areas of Hainan Province, China.

Anopheles sinensis is one of the major malaria vectors and among the dominant species in Hainan Province, China. The resistance of An. sinensis to insecticides is an important threat to malaria control. However, few reports on insecticide resistance of An. sinensis were reported in this area. Eight districts in Hainan Province were selected as the study areas. Insecticide susceptibility bioassays were tested on wild-caught female mosquitoes of An. sinensis to 4% dichlorodiphenyltrichloroethane (DDT), 0.05% deltamethrin, and 5% malathion by using the World Health Organization standard resistance tube assay procedure. All the tested An. sinensis mosquitoes demonstrated resistance to 4% DDT, with less than 72% mortality in the standard assay. The populations from Baisha and Qiongzhong demonstrated possible resistance to 0.05% deltamethrin, with 94-95% mortality, whereas the populations from other districts demonstrated resistance to 0.05% deltamethrin in the standard assay. The populations from Baisha, Qiongzhong, and Dongfang demonstrated susceptibility to 5% malathion, but the populations from other districts demonstrated resistance. These results facilitate the improvement of effective control strategies for malaria vector mosquitoes in Hainan.

A Cost-Effectiveness Analysis of Plasmodium falciparum Malaria Elimination in Hainan Province, 2002-2012.

In Hainan Province, China, great achievements in elimination of falciparum malaria have been made since 2010. There have been no locally acquired falciparum malaria cases since that time. The cost-effectiveness of elimination of falciparum malaria has been analyzed in Hainan Province. There were 4,422 falciparum malaria cases reported from 2002 to 2012, more cases occurred in males than in females. From 2002 to 2012, a total of 98.5 disability-adjusted life years (DALYs) were reported because of falciparum malaria. Populations in the age ranges of 15-25 and 30-44 years had higher incidences and DALYs than other age groups. From 2002 to 2012, malaria-related costs for salaries of staff, funds from the provincial government, national government, and the GFATM were US$3.02, US$2.24, US$1.44, and US$5.08 million, respectively. An estimated 9,504 falciparum malaria cases were averted during the period 2003-2012. The estimated cost per falciparum malaria case averted was US$116.5. The falciparum malaria elimination program in Hainan was highly effective and successful. However, funding for maintenance is still needed because of imported cases.

Sensitivity of Plasmodium falciparum to antimalarial drugs in Hainan Island, China.

Pyronaridine and artesunate have been shown to be effective in falciparum malaria treatment. However, pyronaridine is rarely used in Hainan Island clinically, and artesunate is not widely used as a therapeutic agent. Instead, conventional antimalarial drugs, chloroquine and piperaquine, are used, explaining the emergence of chloroquine-resistant Plasmodium falciparum. In this article, we investigated the sensitivity of P. falciparum to antimalarial drugs used in Hainan Island for rational drug therapy. We performed in vivo (28 days) and in vitro tests to determine the sensitivity of P. falciparum to antimalarial drugs. Total 46 patients with falciparum malaria were treated with dihydroartemisinin/piperaquine phosphate (DUO-COTECXIN) and followed up for 28 day. The cure rate was 97.8%. The mean fever clearance time (22.5 ± 10.6 hr) and the mean parasite clearance time (27.3 ± 12.2 hr) showed no statistical significance with different genders, ages, temperatures, or parasite density (P > 0.05). The resistance rates of chloroquine, piperaquine, pyronarididine, and artesunate detected in vitro were 71.9%, 40.6%, 12.5%, and 0%, respectively (P < 0.0001). The resistance intensities decreased as follows: chloroquine > piperaquine > pyronarididine > artesunate. The inhibitory dose 50 (IC50) was 3.77 × 10(-6) mol/L, 2.09 × 10(-6) mol/L, 0.09 × 10(-6) mol/L, and 0.05 × 10(-6) mol/L, and the mean concentrations for complete inhibition (CIMC) of schizont formation were 5.60 × 10(-6) mol/L, 9.26 × 10(-6) mol/L, 0.55 × 10(-6) mol/L, and 0.07 × 10(-6) mol/L, respectively. Dihydroartemisinin showed a strong therapeutic effect against falciparum malaria with a low toxicity.

[Resistance of Anopheles sinensis to three common insecticides in Hainan Province].

Anopheles sinensis adults were collected by cow-baited trap in Haikou City, Sanya City, Lingshui County, Changjiang County and Qiongzhong County of Hainan Province during 2011-2013. The mosquitoes were exposed to insecticide impregnated papers with discriminating concentrations of DDT (4%), deltamethrin (0.05%), and malathion (5%) using WHO standard assays. Knockdown rate was recorded at 10, 15, 20, 30, 40, 50, and 60 min, and KT50 values were calculated. Mortality was recorded after 24 hours of exposure. The resistance level was graded as sensitive group (S) with a mortality rate of 98%-100%, preliminary resistance group (M) with mortality rate of 80%-97%, and resistance group (R) with mortality rate of lower than 80%. The results showed that the mortality rate of An. sinensis in Qiongzhong County in 24 h-post-exposure to 0.05% deltamethrin was 95.0% with a resistance degree of M. That to 0.05% deltamethrin in the other 4 sites was 17.0%-63.0%, all with a resistance degree of R. That to 4% DDT in Haikou, Sanya, Lingshui, Qiongzhong and Changjiang was 36.0%, 27.0%, 24.0%, 59.1%, and 82.0%, with a resistance level of R, R, R, R, and M, respectively. That to 5% malathion in Haikou, Sanya, and Lingshui was 16.0%-41.0%, all with a resistance degree of R, while that to malathion in Qiongzhong and Changjiang was 100% and 98.0%, respectively, with a resistance level of S.

Eliminating Plasmodium falciparum in Hainan, China: a study on the use of behavioural change communication intervention to promote malaria prevention in mountain worker populations.

BACKGROUND: In the island of Hainan, the great majority of malaria cases occur in mountain worker populations. Using the behavioral change communication (BCC) strategy, an interventional study was conducted to promote mountain worker malaria prevention at a test site. This study found the methods and measures that are suitable for malaria prevention among mountain worker populations. METHODS: During the Plasmodium falciparum elimination stage in Hainan, a representative sampling method was used to establish testing and control sites in areas of Hainan that were both affected by malaria and had a relatively high density of mountain workers. Two different methods were used: a BCC strategy and a conventional strategy as a control. Before and after the intervention, house visits, core group discussions, and structural surveys were utilized to collect qualitative and quantitative data regarding mountain worker populations (including knowledge, attitudes, and practices [KAPs]; infection status; and serological data), and these data from the testing and control areas were compared to evaluate the effectiveness of BCC strategies in the prevention of malaria. RESULTS: In the BCC malaria prevention strategy testing areas, the accuracy rates of malaria-related KAP were significantly improved among mountain worker populations. The accuracy rates in the 3 aspects of malaria-related KAP increased from 37.73%, 37.00%, and 43.04% to 89.01%, 91.53%, and 92.25%, respectively. The changes in all 3 aspects of KAP were statistically significant (p < 0.01). In the control sites, the changes in the indices were not as marked as in the testing areas, and the change was not statistically significant (p > 0.05). Furthermore, in the testing areas, both the percentage testing positive in the serum malaria indirect fluorescent antibody test (IFAT) and the number of people inflicted decreased more significantly than in the control sites (p < 0.01). CONCLUSION: The use of the BCC strategy significantly improved the ability of mountain workers in Hainan to avoid malarial infection. Educational and promotional materials and measures were developed and selected in the process, and hands-on experience was gained that will help achieve the goal of total malaria elimination in Hainan.

[Resistance assay of malaria vectors to four kinds of common insecticides in some endemic areas of Hainan Province].

OBJECTIVE: To determine the resistance of malaria vectors to four kinds of common insecticides in some endemic areas of Hainan Province. METHODS: Anopheline mosquitoes were collected between 2008 and 2010 from malaria endemic areas where insecticides were used for years. Anopheles dirus were collected from human-baited trap in Wangxia Town of Changjiang County. An. minimus and An. sinensis were collected by cow-baited trap in Jiangbian Town of Dongfang City. F0 generation female An. sinensis, F1 generation of female An. dirus and An. minimus were selected and exposed to insecticide impregnated papers with discriminating concentrations of DDT (4%), deltamethrin (0.05%), cyfluthrin (0.15%), and malathion (5%) using WHO standard assays. Knockdown rate was recorded at 10, 15, 20, 30, 40, 50, and 60 min, and KTm values were calculated. Mortality was recorded after 24 hours of exposure. RESULTS: Mortality in An. dirus was 100% to DDT, deltamethrin and malathion. Knockdown rate of An. dirus exposed to DDT and deltamethrin was 82.0% and 100%, with a KT50 value of 46.9 and 18.4 min, respectively. Mortality of An. minimus to DDT, deltamethrin, cyfluthrin and malathion was 98.1%, 99.0%, 100%, and 100%, respectively. The knockdown rate of An. minimus to DDT, deltamethrin, and cyfluthrin was 96.3%, 99.0%, and 100%, respectively, and the KTs value was 31.3, 16.8, and 7.4 min, respectively. Mortality of An. sinensis to DDT, deltamethrin, and malathion was 19.8%, 22.9%, and 43.8%, respectively. Knockdown rate of An. sinensis to DDT and deltamethrin was 2.0%, the KT50 can not be calculated. CONCLUSION: An. dirus and An. minimus, the main malaria vectors in the survey sites of Hainan Province, are susceptible to the four insecticides, while secondary malaria vector An. sinensis showed resistance to DDT, deltamethrin, and malathion.