The colonization of pyrethroid resistant strain from wild Anopheles sinensis, the major Asian malaria vector

From Global to Local-New Insights into Features of Pyrethroid Detoxification in Vector Mosquitoes

The threat of mosquito-borne diseases continues to be a problem for public health in subtropical and tropical regions of the world; in response, there has been increased use of adulticidal insecticides, such as pyrethroids, in human habitation areas over the last thirty years. As a result, the prevalence of pyrethroid-resistant genetic markers in natural mosquito populations has increased at an alarming rate. This review details recent advances in the understanding of specific mechanisms associated with pyrethroid resistance, with emphasis on features of insecticide detoxification and the interdependence of multiple cellular pathways. Together, these advances add important context to the understanding of the processes that are selected in resistant mosquitoes. Specifically, before pyrethroids bind to their targets on motoneurons, they must first permeate the outer cuticle and diffuse to inner tissues. Resistant mosquitoes have evolved detoxification mechanisms that rely on cytochrome P450s (CYP), esterases, carboxyesterases, and other oxidation/reduction (redox) components to effectively detoxify pyrethroids to nontoxic breakdown products that are then excreted. Enhanced resistance mechanisms have evolved to include alteration of gene copy number, transcriptional and post-transcriptional regulation of gene expression, as well as changes to cellular signaling mechanisms. Here, we outline the variety of ways in which detoxification has been selected in various mosquito populations, as well as key gene categories involved. Pathways associated with potential new genes of interest are proposed. Consideration of multiple cellular pathways could provide opportunities for development of new insecticides.

Malaria Elimination in China: Improving County-Level Malaria Personnel Knowledge of the 1-3-7 Strategy through Tabletop Exercises

As China moves to the prevention of reestablishment of malaria, maintaining skills for malaria in county personnel on the "1-3-7" surveillance and response strategy is critical. China's "1-3-7" strategy defines targets used to guide and monitor malaria case reporting, investigation, and response, respectively: reporting of malaria cases within 1 day, their confirmation and investigation within 3 days, and the appropriate public health response to prevent further transmission within 7 days. Assessing the knowledge of local CDC malaria personnel on the "1-3-7" surveillance and response strategy is urgently needed. In June 2016, two different training modules (classroom-style teaching and tabletop exercises) were conducted for 125 CDC staff in Jiangsu Province, China, to determine the effectiveness of the two training modules on CDC staff knowledge and learning of the "1-3-7" strategy. The classroom-style training module just imparted the malaria knowledge to participants through teaching. Tabletop exercises were carried out through discussion-based scenarios using questions and answers on the "1-3-7" strategy. Questionnaires assessing knowledge improvement were designed and administered to personnel responsible for malaria surveillance and response activities, including at baseline and end line. Overall, knowledge of the "1-3-7" strategy for malaria elimination was 63.2% correct at baseline, 70.6% after implementing a classroom-style teaching module (χ2 = 11.20, P = 0.001), and 84.6% after the tabletop exercise module (χ2 = 48.82, P < 0.001). The knowledge of each component of the "1-3-7" strategy improved significantly after the tabletop exercise module. The total proportion of respondents with a high score (greater than or equal to 75%) was 82.7% in the classroom-style module and 95.2% in the tabletop exercise module. The proportion of respondents with a high score significantly increased after tabletop exercises in the stratified demographic groups of men who work at the county CDC level, have a bachelor's degree, hold a professional title as professor or assistant, are aged 31-50 years, and have attained 11-20 years of service with the CDC compared with the classroom-style module. Acceptability of the classroom-style module (78.2%) compared with tabletop exercises (94.4%) by the CDC malaria personnel increased significantly (χ2 = 11.96, P = 0.004). Feedback from participants on the modules suggest the tabletop exercises were an effective training method, which could maintain and improve the knowledge and capacity for malaria surveillance and response in basic CDC level personnel in China.

The increasing importance of Plasmodium ovale and Plasmodium malariae in a malaria elimination setting: an observational study of imported cases in Jiangsu Province, China, 2011-2014

Background

Following initiation of China’s National Malaria Elimination Action Plan in 2010, indigenous malaria infections in Jiangsu Province decreased significantly. Meanwhile imported Plasmodium infections have increased substantially, particularly Plasmodium ovale and Plasmodium malariae. Given the risk for malaria resurgence, there is an urgent need to understand the increase in imported P. ovale and P. malariae infections as China works to achieve national malaria elimination.

Methods

An observational study of imported malaria cases in Jiangsu Province, China was carried out for the period of 2011–2014.

Results

A total of 1268 malaria cases were reported in Jiangsu Province from 2011 to 2014. Although imported Plasmodium falciparum cases (n = 1058) accounted for 83.4 % of all reported cases in Jiangsu, P. ovale cases (14, 19, 30, and 46) and their proportion (3.7, 9.6, 8.8, and 13.0 %) of all malaria cases increased over the 4 years. Similarly, P. malariae cases (seven, two, nine, and 10) and proportion (1.9, 1.0, 2.6, and 2.8 %) of all malaria cases increased slightly during this time. A total of 98 cases of Plasmodium ovale curtisi (47/98, 48 %) and Plasmodium ovale wallikeri (51/98, 52 %) were identified as well. Latency periods were significant among these Plasmodium infections (p = 0.00). Also, this study found that the latency periods of P. ovale sp., P. malariae and Plasmodium vivax were significantly longer than P. falciparum. However, for both P. ovale curtisi and P. ovale wallikeri infections, the latency period analysis was not significant (p = 0.81). Misdiagnosis of both P. ovale and P. malariae was greater than 71.5 and 71.4 %, respectively. The P. ovale cases were misdiagnosed as P. falciparum (35 cases, 32.1 %), P. vivax (43 cases, 39.4 %) by lower levels of CDCs or hospitals. And, the P. malariae cases were misdiagnosed as P. falciparum (ten cases, 35.7 %), P. vivax (nine cases, 32.1 %) and P. ovale sp. (one case, 3.6 %). Geographic distribution of imported P. ovale sp. and P. malariae cases in Jiangsu Province mainly originated from sub-Saharan Africa such as Equatorial Guinea, Nigeria, and Angola.

Conclusions

Although the vast majority of imported malaria cases were due to P. falciparum, the increase in other rare Plasmodium species originating from sub-Saharan Africa and Southeast Asia should be closely monitored at all levels of health providers focusing on diagnosis and treatment of malaria. In addition to a receptive vector environment, long latency periods and misdiagnosis of P. malariae and P. ovale sp. increase the risk of re-introduction of malaria in China.

Genomic Analysis of Detoxification Supergene Families in the Mosquito Anopheles sinensis

Anopheles sinensis is an important malaria vector in China and other Southeast Asian countries, and the emergence of insecticide resistance in this mosquito poses a serious threat to the efficacy of malaria control programs. The recently published An. sinensis genome and transcriptome provide an opportunity to understand the molecular mechanisms of insecticide resistance. Analysis of the An. sinensis genome revealed 174 detoxification genes, including 93 cytochrome P450s (P450s), 31 glutathione-S-transferases (GSTs), and 50 choline/carboxylesterases (CCEs). The gene number was similar to that in An. gambiae, but represented a decrease of 29% and 42% compared with Aedes aegypti and Culex quinquefasciatus, respectively. The considerable contraction in gene number in Anopheles mosquitoes mainly occurred in two detoxification supergene families, P450s and CCEs. The available An. sinensis transcriptome was also re-analyzed to further identify key resistance-associated detoxification genes. Among 174 detoxification genes, 124 (71%) were detected. Several candidate genes overexpressed in a deltamethrin-resistant strain (DR-strain) were identified as belonging to the CYP4 or CYP6 family of P450s and the Delta GST class. These generated data provide a basis for identifying the resistance-associated genes of An. sinensis at the molecular level.