Jabeur Daaboub

Resistance to pyrethroid insecticides in Culex pipiens pipiens (Diptera: Culicidae) from Tunisia

Resistance toward 2 pyrethroïd insecticides (permethrin and deltamethrin), and an organochloric one (DDT) was analyzed in 18 samples of Culex pipiens pipiens common mosquitoes collected from different Tunisian areas between March 2002 and November 2005. Bioassays were performed over different larvae samples. The recorded mortalities, after 24h exposure to increased doses of insecticides, were compared to those obtained on a susceptible reference strain (S-LAB). All samples were resistant to permethrin. However, a large variation in the tolerance to this insecticide was observed between samples. Resistance ratio levels at LC50 (RR50) for the analyzed samples were ranged from 1.5 to 9092 folds. For deltamethrin, 14 among 17 studied samples were resistant. RR50, in the resistant samples, were ranged from 3 to 453 folds. Resistance to the two tested pyrethroids and DDT were correlated. The use of synergists showed that the cytochrome P450-dependent monooxygenases had a major contribution to the permethrin and deltamethrin resistance and that the esterases (and/or glutathione-S-transferases) had only a minor contribution. Results were discussed in relation to resistance mechanisms and mosquitos control.

Larval habitats characterization and species composition of Anopheles mosquitoes in Tunisia, with particular attention to Anopheles maculipennis complex.

In Tunisia, malaria transmission has been interrupted since 1980. However, the growing number of imported cases and the persistence of putative vectors stress the need for additional studies to assess the risk of malaria resurgence in the country. In this context, our aim was to update entomological data concerning Anopheles mosquitoes in Tunisia. From May to October of 2012, mosquito larval specimens were captured in 60 breeding sites throughout the country and identified at the species level using morphological keys. Environmental parameters of the larval habitats were recorded. Specimens belonging to the An. maculipennis complex were further identified to sibling species by the ribosomal deoxyribonucleic acid (rDNA)-internal transcribed spacer 2 (ITS2) polymerase chain reaction (PCR) technique. In total, 647 Anopheles larvae were collected from 25 habitats. Four species, including An. labranchiae, An. multicolor, An. sergentii, and An. algeriensis, were morphologically identified. rDNA-ITS2 PCR confirmed that An. labranchiae is the sole member of the An. maculipennis complex in Tunisia. An. labranchiae was collected throughout northern and central Tunisia, and it was highly associated with rural habitat, clear water, and sunlight areas. Larvae of An. multicolor and An. sergentii existed separately or together and were collected in southern Tunisia in similar types of breeding places.

Comparison of chlorpyrifos resistance in Culex pipiens pipiens (Diptera: Culicidae) collected from Northern and Southern Tunisia: Chlorpyrifos Resistance in Culex pipiens

In this study, we investigated resistance to the organophosphates chlorpyrifos in Tunisian populations of Culex pipiens pipiens. Three field populations were collected from Northern and central Tunisia between 2003 and 2005 and used for the bioassays tests. Our results registered moderate and high levels of resistance to chlorpyrifos which ranged from 33.8 to 111. The chlorpyrifos resistant populations were highly resistant to propoxur indicated an insensitive acetylcholinesterase 1 (AChE 1). The highest frequency of AChE 1 resistant phenotypes (64%) was recorded in the most resistant population (sample # 1). Bioassays conducted in the presence of synergists showed that not esterases were involved as the resistance mechanism to chlorpyrifos. However, CYP450 was partly involved in the resistance of the most resistant sample (# 1). Starch electrophoresis showed that three esterases were present in studied samples: A2‐B2, A4‐B4 and B12. Results are discussed in relation to the selection pressure caused by insecticide treatments.

First study of susceptibility and resistance status to pyrethroids insecticides in Anopheles (Cellia) sergentii (Theobald, 1907) from Southern Tunisia

Background Insecticide resistance is an important threat to malaria control. Anopheles (An.) sergentii proved to be the number one vector in the oases and may be of a particular interest in projection of the future trends of the disease in Tunisia. Objectives Resistance status to pyrethroids insecticides in An. sergentii was evaluated for the first time in Tunisia. Methods Diagnostic resistance tests to pyrethroids insecticides were conducted on late third and early fourth larvae of An. sergentii collected in Southern Tunisia. Results The level of resistance to permethrin and deltamethrin varied from 1.9 to 5.77 and from 2.75 to 4.63, respectively. The highest resistance was recorded in sample # 3 to the two used insecticides. Synergists showed that esterases and glutathione-S-transferase were not involved in the resistance to any of the evaluated insecticides. In contrast, cytochrome-P450 monooxygenases played a role in the detoxification of two among three studied samples. Positive correlations between larval tolerance to both Permethrin/DDT and Deltamethrin/DDT were recorded indicated target site insensitivity. Conclusion Continued monitoring of insecticide susceptibility and generating complementary data on mechanisms of resistance using molecular and biochemical methods is essential to ensure early detection of insecticide resistance in potential malaria vectors in Tunisia.

First studies showing high temephos resistance in Anopheles labranchiae (Diptera: Culicidae) from Tunisia

Background Despite the public health importance of Anopheles (An.) labranchiae, their resistance status to temephos insecticide has not, to our knowledge, been explored. Objectives The present study was carried out to determine the temephos resistance status of field populations of An. labranchiae from Tunisia. Methods Six field populations of An. labranchiae were collected as larvae from breeding sites of Northern and Central Tunisia. All the tests were carried out according to the WHO method. Results Results reported that the majority of field populations showed low and medium resistance ratios (6.2<RR50< 29.8) to temephos insecticide tested except for the strain # 1 which had interestingly a very high resistance with RR50 of 624 never detected in Tunisia and North Africa even on other species of mosquitoes Conclusion The resistance ratios of this species were higher than recorded in other countries. Biochemical and molecular studies would be of great importance to identify the mechanisms involved in the recorded resistance to temephos.

West Nile Virus: An Overview of its Recent Spread in the Mediterranean Basin

West Nile virus (WNV) is transmitted to humans through infected Culex mosquito. It causes a sudden fever, but also, more rarely, neuroinvasive infections. Since its first identification in East Africa, the virus has been identified on all continents. The subject of this article was to review its spread in the Mediterranean basin until recently. It is very important for the implementation and development of control strategies to minimize risk of WNV emergence in the Mediterranean basin. Available data were used to assemble and synthesize information. West Nile virus has become endemic/enzootic in Eastern Europe and the Mediterranean basin. In other regions such as the South of France, Portugal and the Maghreb, the virus causes sporadic cases in both humans and equidae. Since 2010, there has been an increase in the number of cases, as well as an extent of the endemic area. The endemic area will probably increase in coming decades because of climate change, especially in the north and west, and thus reach previously unharmed areas.

Mosquitoes (Diptera: Culicidae) in Tunisia, with Particular Attention to Proven and Potential Vectors: A Review

The state of knowledge of mosquitoes (Diptera: Culicidae) is dispersed and disorganized in Tunisia although their important role as disease vectors. The available published and unpublished reports were collected and reviewed. There are about 43 species of mosquitoes in Tunisia. There are a total of 12 species of Anopheles. The species involved in malaria transmission in Tunisia during the endemic period and still persisting in Tunisia are Anopheles (An.) labranchiae, predominant species in the north and center of the country, An. sergenti and An. multicolor in the Center and South. The genus Culex contains 11 species. Culex (Cx.) pipiens is the most dangerous specie and their distribution is ubiquitous in Tunisia. This mosquito has been implicated in the transmission of West Nile virus (WNV) in Tunisia. Concerning vectors, Aedes aegypti was reported in Tunisia before 2000, but was not encountered later. Moreover, Aedes albopictus, the other vector of Dengue and Chikungunya, is not among the 43 species of mosquitoes described in Tunisia, but the latter circulates in neighboring countries. Collected and analyzed data will help current and future research on mosquitoes particularly in the field of medical entomology to develop and implement vector control strategies.

A Review of Entomological Surveillance and Vector Control, with Concrete Examples that Discuss the Use of Indicators in Monitoring and Evaluation

The emergence of diseases or vectors is not a new phenomenon but for the last few decades, it seems to be accelerating. The subject of this article was to review the surveillance and response to disease emergence, in particular entomological surveillance. The available published and unpublished reports on entomological surveillance and vector control were collected and reviewed. The relevant entomological indicators target the presence/absence, density or longevity of vector populations, or even the presence of pathogens in the vectors. The role of research is to fill gaps and limit uncertainties that may affect the efficiency of an entomological surveillance program, including vector competence and environmental conditions favorable to emergence and outbreaks.