Differential Disrupting Effects of Prolonged Low-Dose Exposure to Dichlorodiphenyltrichloroethane on Androgen and Estrogen Production in Males.

Dichlorodiphenyltrichloroethane (DDT) is the most widespread, persistent pollutant and endocrine disruptor on the planet. Although DDT has been found to block androgen receptors, the effects of its low-dose exposure in different periods of ontogeny on the male reproductive system remain unclear. We evaluate sex steroid hormone production in the pubertal period and after maturation in male Wistar rats exposed to low doses of o,p'-DDT, either during prenatal and postnatal development or postnatal development alone. Prenatally and postnatally exposed rats exhibit lower testosterone production and increased estradiol and estriol serum levels after maturation, associated with the delayed growth of gonads. Postnatally exposed rats demonstrate accelerated growth of gonads and higher testosterone production in the pubertal period. In contrast to the previous group, they do not present raised estradiol production. All of the exposed animals exhibit a reduced conversion of progesterone to 17OH-progesterone after sexual maturation, which indicates putative attenuation of sex steroid production. Thus, the study reveals age-dependent outcomes of low-dose exposure to DDT. Prenatal onset of exposure results in the later onset of androgen production and the enhanced conversion of androgens to estrogens after puberty, while postnatal exposure induces the earlier onset of androgen secretion.

'We spray and walk away': wall modifications decrease the impact of indoor residual spray campaigns through reductions in post-spray coverage.

Malaria prevalence has significantly reduced since 2000, largely due to the scale-up of vector control interventions, mainly indoor residual spraying (IRS) and long-lasting insecticide-treated nets (LLINs). Given their success, these tools remain the frontline interventions in the fight against malaria. Their effectiveness relies on three key ingredients: the intervention, the mosquito vector and the end-user. Regarding the intervention, factors such as the insecticide active ingredient(s) used and the durability and/or bio-efficacy of the tool over time are critical. For the vectors, these factors include biting and resting behaviours and the susceptibility to insecticides. Finally, the end-users need to accept and properly use the intervention. Whilst human attitude and behaviour towards LLINs are well-documented both during and after distribution, only initial coverage is monitored for IRS and in a few geographic settings the residual efficacy of the used product. Here, the historical evidence on end-users modifying their wall surfaces post-spraying is presented, a behaviour that has the potential to reduce actual IRS coverage, effectiveness and impact, as fewer people are truly protected. Therefore, clear guidelines on how to monitor IRS acceptability and/or coverage, both before, during and after spraying, are urgently needed as part of the Monitoring and Evaluation of malaria programmes.

Exposures to the environmental toxicants pentachlorophenol (PCP) and dichlorodiphenyltrichloroethane (DDT) modify secretion of interleukin 1-beta (IL-1ß) from human immune cells.

Pentachlorophenol (PCP) and Dichlorodiphenyltrichloroethane (DDT) are environmental contaminants found in human blood. Previous studies have shown that PCP and DDT inhibit the lytic function of highly purified human natural killer (NK) lymphocytes and decrease the expression of several surface proteins on NK cells. Interleukin-1 ßeta (IL-1ß) is a cytokine produced by lymphocytes and monocytes, and anything that elevates its levels inappropriately can lead to chronic inflammation, which among other consequences can increase tumor development and invasiveness. Here, PCP and DDT were examined for their ability to alter secretion of IL-1ß from immune cell preparations of various complexity: NK cells; monocyte-depleted (MD) peripheral blood mononuclear cells (PBMCS); and PBMCs. Cells were exposed to concentrations of PCP ranging from 5 to 0.05 µM and DDT concentrations of 2.5-0.025 µM for 24, 48 h, and 6 days. Results showed that both PCP and DDT increased IL-1ß secretion from all of the immune cell preparations. The specific concentrations of PCP and DDT that increased IL-1ß secretion varied by donor. Immune cells from all donors showed compound-induced increases in IL-1ß secretion at one or more concentration at one or more length of exposure. The mechanism of PCP stimulation of IL1-ß secretion was also addressed, and it appears that the MAPKs, ERK1/2 and p38, may be utilized by PCP to stimulate secretion of IL-1ß.

Historical pesticide applications coincided with an altered diet of aerially foraging insectivorous chimney swifts.

Numerous environmental pressures have precipitated long-term population reductions of many insect species. Population declines in aerially foraging insectivorous birds have also been detected, but the cause remains unknown partly because of a dearth of long-term monitoring data on avian diets. Chimney swifts (Chaetura pelagica) are a model aerial insectivore to fill such information gaps because their roosting behaviour makes them easy to sample in large numbers over long time periods. We report a 48-year-long (1944-1992) dietary record for the chimney swift, determined from a well-preserved deposit of guano and egested insect remains in Ontario (Canada). This unique archive of palaeo-environmental data reflecting past chimney swift diets revealed a steep rise in dichlorodiphenyltrichloroethane (DDT) and metabolites, which were correlated with a decrease in Coleoptera remains and an increase in Hemiptera remains, indicating a significant change in chimney swift prey. We argue that DDT applications decimated Coleoptera populations and dramatically altered insect community structure by the 1960s, triggering nutritional consequences for swifts and other aerial insectivores.

Resting behaviour of Anopheles stephensi type form to assess its amenability to control malaria through indoor residual spray.

BACKGROUND & OBJECTIVES: In the present study, an attempt was made to find reasons of ineffectiveness of indoor residual spray to interrupt malaria transmission by investigating the behaviour of two variants of Anopheles stepnesi, viz. type form and mysorensis in rural areas of Rajasthan, India. METHODS: Both low malarious (DDT spray from 1958 to 1976) and high malarious (DDT spray from 1958 to April 2006) villages were selected for the study in Arid zone district Jodhpur, Rajasthan during March-April 2006. Resting behaviour of the species during all its movement rhythms covering 24 h period related to: (i) swarming/ mating; (ii) pre- and post-biting rest; (iii) after feed resting between hoping movements; (iv) night and day time resting and; (v) diel activity movements in response to temperature changes, were carried out. RESULTS: The results showed that household objects like cupboards, furnitures, hanging clothes, goods stacked on loft, stored clothes, cobwebs and floor were the dominant resting sites both in sprayed and unsprayed villages. About 95 and 97% of An. stephensi preferred to rest on household objects of unsprayed and sprayed villages respectively. There was no significant difference in resting behaviour of the species in both groups of villages (p >0.05). The pre-biting resting time was recorded as 5 to 15 min whereas post-biting resting time lasted for 15 to 25 min. After biting outdoor (in courtyard--open to sky) species starts entering the rooms at around 2330 hrs. It was observed that during III quarter (0100 to 0400 hrs) maximum species entered into the room were 56% in unsprayed and 62% in sprayed villages. Statistically there was no significant difference in the entry of mosquitoes (p >0.05) in both the groups of villages. CONCLUSION: Before DDT era, An. stephensi was found resting at all heights of the walls inside the human dwellings. Present study revealed that An. stephensi is trying to avoid sprayable surfaces and tend to rest on unsprayable surfaces during all its movement rhythms starting from swarming, pre-/post-biting and during hopping movements in the courtyard and thereafter household objects inside the room as final day time resting. It was concluded that changed behaviour of resting of An. stephensi on unsprayable objects in sprayed rooms largely accounted for failure of malaria control. Control of An. stephensi, thus requires an integrated vector control strategy based upon interesectoral, environmental, larviciding with chemical/biolarvicide and use of larvivorous fish wherever feasible. Such a control strategy offers cost-effective and sustainable option than indoor residual spray.

What drives community adherence to indoor residual spraying (IRS) against malaria in Manhiça district, rural Mozambique: a qualitative study.

BACKGROUND: Malaria control remains a challenge in sub-Saharan Africa. In 2006, the World Health Organization (WHO) reinforced the recommendation of indoor residual spraying (IRS) with dichlorodiphenyltrichloroethane (DDT) to reduce malaria transmission. The National Malaria Control Programme has been reporting high coverage rates of IRS in Mozambique. It is important to establish to what extent these rates are a reflection of community acceptability, and to explore the factors associated with adherence, in order to recommend suitable approaches for interventions of this nature. OBJECTIVE: To understand the implementation process, reception and acceptability of the IRS program in Manhiça district, Southern Mozambique. METHODS: Qualitative data was collected through in-depth interviews, participant observation of IRS activities, informal interviews, and focus group discussions. Study participants comprised householders, community leaders, health care providers, sprayers, and community members. Qualitative data analysis was based on grounded theory. Secondary data from the Manhiça Demographic Surveillance System was used to complement the qualitative data. RESULTS: IRS was well received in most neighbourhoods. The overall coverage rates varied between 29% and 41% throughout the study period. The factors related to adherence to IRS were: immediate impact on insects in general, trust and obedience in the health authority, community leaders' influence, and acquaintance with the sprayers. Fighting malaria was not an important motivation for IRS adherence. There was a perception of limited efficacy of IRS against mosquitoes, but this did not affect adherence. Non-adherence to the intervention was mainly due to the unavailability of key householders, disagreement with the procedures, and the perception that spraying increased the burden of insects. Most respondents strongly favoured bed nets over IRS. CONCLUSION: The study suggests that the contribution of IRS to malaria and mosquito control is not entirely perceived by the beneficiaries, and that other as cost effective interventions such as insecticide-treated nets are favoured over IRS. Adherence to IRS was found to be influenced by socio-political factors. There is a need to redefine the community sensitization approaches in order to make IRS a genuinely participative, acceptable, and sustainable programme.

How does background affect attitudes to socioscientific issues in Taiwan?

Based upon the goal of scientific literacy and the importance of socioscientific issues (SSIs), the purpose of this study was to investigate the Taiwanese public's awareness of, inclinations to buy/use, and their attitudes towards three attributes of SSIs including genetically modified food (GM food), organic food, and DDT and malaria (DDT). Data from a total of 865 participants across ten populations (six different educational levels and four different vocations) were validated and analyzed. The results revealed that the awareness regarding GM food and DDT increased with the levels of education. The inclinations to buy/use and the attitudes towards the three SSIs, were not related to levels of education, vocation or gender, but were related to attributes of the SSIs. The implications for education and policy development are discussed.

Cationic lipid/pDNA complex formation as potential generic method to generate specific IRF pathway stimulators.

Cationic liposome - CpG DNA complexes (lipoplexes) are known as stimulators of innate immunity via Toll-like receptor 9 (TLR9)-triggered activation of the nuclear factor kappa B (NF-κB) pathway. More recent reports suggest that DNA lipoplexes also engage DNA sensors in the cytosol leading to the stimulation of the interferon response factor (IRF) pathway. In this study a range of lipoplexes were formulated by using an invariable helper lipid, three different cationic lipids (DOTAP, DOTMA and DDA) and three different CpG-containing plasmids of different sizes. These lipoplexes exhibited similar hydrodynamic diameters, zeta-potentials and plasmid loading rates, despite the different lipid blends and CpG-containing plasmids. Binding and uptake of liposomal lipids by J774.A1 macrophages and JAWSII dendritic cells increased significantly (up to 4-fold) upon lipoplex formation. Cellular plasmid DNA uptake via lipoplexes compared to naked DNA was increased up to 18-fold. Analysis of signal transduction pathway activation in J774-DUAL™ reporter cells by liposomes or naked CpG plasmid DNA compared to their derived lipoplexes showed only minor activation of the NF-κB pathway, while the IRF pathway displayed massive activation factors of up to 46-fold. DOTAP- and DOTMA lipoplexes also led to massive interferon-alpha and -beta secretion of J774A.1 macrophages and JAWSII dendritic cells, which is a hallmark of IRF pathway activation. Cellular distribution studies on DOTAP lipoplexes suggest delivery of plasmid DNA via vesicular compartments into the cytosol. Taken together, the CpG plasmid DNA lipoplexes generated in this study appear to selectively stimulate DNA receptors activating the IRF pathway, while bypassing TLR9 and NF-κB activation.

Program to eradicate malaria in Sardinia, 1946-1950.

During 1946-1950, the Rockefeller Foundation conducted a large-scale experiment in Sardinia to test the feasibility of indigenous vector species eradication. The interruption of malaria transmission did not require vector eradication, but with a goal of developing a new strategy to fight malaria, the choice was made to wage a rapid attack with a powerful new chemical. Costing millions of dollars, 267 metric tons of DDT were spread over the island. Although malaria was eliminated, the main objective, complete eradication of the vector, was not achieved. Despite its being considered almost eradicated in the mid-1940s, malaria 60 years later is still a major public health problem throughout the world, and its eradication is back on the global health agenda.

Molecular analysis of knock down resistance (kdr) mutation and distribution of kdr genotypes in a wild population of Culex quinquefasciatus from India.

OBJECTIVE: To investigate the presence of knock down resistance (kdr) mutation, its frequency distribution in the principal vector of bancroftian filariasis, Culex quinquefasciatus from northeastern India, and to relate kdr genotypes with susceptibility and/or resistance to DDT and deltamethrin in this vectors. METHODS: Adult female mosquitoes were collected by aspiration from human dwellings in two villages, Benganajuli and Rikamari, and two military establishments, Field Units I and II. Insecticide susceptibility tests were performed following WHO methods with 4% DDT and 0.05% deltamethrin. Molecular identification of kdr mutation and genotyping of kdr locus was performed by allele-specific PCR (AS-PCR) and direct sequencing in a subset of samples. RESULTS: Mosquitoes were resistant to DDT and showed 11.9-41.2% mortality, whereas the knock down bioassay for deltamethrin suggests complete susceptibility to this insecticide in all study sites except Benganajuli. The result of AS-PCR confirmed the presence of three genotypes: susceptible (SS), resistant (RR) and heterozygous (SR) in the population. Genotype frequencies at kdr locus for DDT-resistant individuals conformed with the Hardy-Weinberg proportion, whereas DDT and deltamethrin susceptible individuals differed significantly (P < 0.05). The efficacy of AS-PCR in detecting the correct genotype was not encouraging. CONCLUSIONS: This is the first report from India on kdr genotyping in C. quinquefasciatus, and it confirms the occurrence of kdr allele in this vector in northeastern India. This finding has serious implications for the filariasis control programmes in India.

Nonconversion of o,p'-DDT to p,p'-DDT in rats, sheep, chickens, and quail.

The finding of appreciable quantities of p,p'-DDT after feeding o,p'-DDT to rats led to the proposal of a theory, that an isomeric metabolic conversion occurs. The presence of p,p'-DDT as an impurity in supposedly pure samples of o,p'-DDT is the correct explanation for the appearance of p,p'-DDT. Purified o,p'-DDT and (14)C-labeled o,p'-DDT yielded no data to support the idea that o,p'-DDT is converted to the p,p'-DDT isomer.

DDT administered to neonatal rats induces persistent estrus syndrome.

The o,p'-isomer of the insecticide DDT when injected into neonatal female rats significantly advanced puberty, induced persistent vaginal estrus after a period of normal estrous cycles, and caused the ovaries to develop follicular cysts and a reduced number of corpora lutea. The uterotropic response to administered estradiol was reduced, and the female pattern of mating behavior was slightly disturbed. Residues of DDT in ovarian, brain, and adipose tissues of the adult animals were the same in both treated and control groups.

Reproductive and developmental effects of transovarian exposure to o,p'-DDT in Japanese quails.

Avian species have the possible risk of embryonic exposure to persistent, lipophilic environmental contaminants, such as dichlorodiphenyltrichloroethane (DDT), by transfer of chemicals accumulated in mother birds to eggs. To model developmental and reproductive disorders of wild birds living in contaminated areas, we exposed Japanese quails in ovo to o,p'-DDT prior to incubation. A positive estrogenic substance diethylstilbestrol (DES; 1 and 10 ng/g of egg) and o,p'-DDT (1-100 microg/g of egg) were injected into the yolk before incubation. Treatment with o,p'-DDT (10 or 100 microg/g) but not with DES significantly reduced the hatchability of eggs. After sexual maturation, o,p'-DDT affected eggshell formation in female quails but had little influence on laying; high doses of o,p'-DDT significantly reduced eggshell strength, shell weight, and shell thickness, and several females treated with 100 microg o,p'-DDT/g laid eggs lacking shells. Diethylstilbestrol decreased egg production itself but had little effect on the eggshell. Both o,p'-DDT and DES caused dose-dependent shortening of the left oviduct and abnormal development of the right oviduct in females, while testis asymmetry was observed in males treated with a high dose of DES. In the uterus of the oviduct, the mRNAs for calcium-regulating factors osteopontin and calbindin D28K were reduced by both treatments, particularly that with o,p'-DDT. The results indicated that transovarian exposure to o,p'-DDT could bring about population declines in avian species through loss of fecundity caused by depression of hatchability and dysfunction of the reproductive tract.

A report on the indoor residual spraying (IRS) in the control of Phlebotomus argentipes, the vector of visceral leishmaniasis in Bihar (India): an initiative towards total elimination targeting 2015 (Series-1).

BACKGROUND & OBJECTIVES: Visceral leishmaniasis, commonly known as kala-azar is endemic in Bihar state, India. Current vector control programme in Bihar focuses mainly on spraying the sandfly infested dwellings with DDT. The Government of India in collaboration with WHO has fixed the target 2015 for total elimination of kala-azar. The present study was carried out to see the impact of DDT and improved IEC in the containment of vector density vis-à-vis disease transmission. METHODS: Before the start of the spraying operations training was imparted to all the medical and paramedical personnel regarding the methods of spraying operations. Pre- and post-sandfly density was monitored in four selected districts. Incidences of kala-azar cases were compared for pre- and post-spray periods. Social acceptability and perceptions of households was collected through questionnaires from 500 randomly selected households in the study districts. RESULTS: House index in three study districts reduced considerably during post-spray when compared to pre-spray. Kala-azar incidence in many districts was reduced after the DDT spray. Either partial or complete refusal was reported in 14.4%, while 35% were not satisfied with the suspension concentration and coverage; and 46.6% were found satisfied with the spraying procedure. INTERPRETATION & CONCLUSION: Strengthening the IEC activities to sensitise the community, proper training of health personnel, monitoring of spray, good surveillance, proper treatment of cases and two rounds of DDT spray with good coverage in the endemic districts up to three years are essential to achieve the desired total elimination of kala-azar in Bihar state.

Comparative efficacy of two rounds of indoor residual spraying of DDT 75% @ 1g/m2 with that of DDT 50% @ 1g/m2 against the malaria vectors in India.

While, dichlorodiphenyl-trichloroethane (DDT) water dispersible powder (WDP) 75% is considered as the high performance long lasting formulation for indoor residual spraying (IRS), no information is available regarding the comparative epidemiological effectiveness of the two DDT formulations when used for IRS in Indian conditions. The current study was undertaken to compare the effectiveness of IRS using DDT WDP 75% @ one g active ingredient (AI)/m2 with that using DDT WDP 50% @ one g AI/m2 in controlling Anopheles fluviatilis and An. culicifacies, the primary vectors of malaria in the selected endemic areas of Odisha State. Although, cone-bioassay mortality after 8 months of post spraying on DDT 75% sprayed surfaces as well as on sprayed but mud plastered surfaces was higher than DDT 50%, the six entomological parameters viz. resting density indoors and outdoors, trap density indoors, parous rate, human blood index and infection rate of An. fluviatilis and An. culicifacies did not show any statistically significant difference in reduction/ changes from pre- to post-spray period between the two DDT formulations.

o,p'-DDT induces cyclooxygenase-2 gene expression in murine macrophages: Role of AP-1 and CRE promoter elements and PI3-kinase/Akt/MAPK signaling pathways.

Dichlorodiphenyltrichloroethane (DDT) has been used as an insecticide to prevent the devastation of malaria in tropical zones. However, many reports suggest that DDT may act as an endocrine disruptor and may have possible carcinogenic effects. Cyclooxygenase-2 (COX-2) acts as a link between inflammation and carcinogenesis through its involvement in tumor promotion. In the present study, we examined the effect of o,p'-DDT on COX-2 gene expression and analyzed the molecular mechanism of its activity in murine RAW 264.7 macrophages. Exposure to o,p'-DDT markedly enhanced the production of prostaglandin E(2) (PGE(2)), a major COX-2 metabolite, in murine macrophages. Furthermore, o,p'-DDT dose-dependently increased the levels of COX-2 protein and mRNA. Transfection with human COX-2 promoter construct, electrophoretic mobility shift assays and DNA-affinity protein-binding assay experiments revealed that o,p'-DDT activated the activator protein 1 (AP-1) and cyclic AMP response element (CRE) sites, but not the NF-kappaB site. Phosphatidylinositol 3 (PI3)-kinase, its downstream signaling molecule, Akt, and mitogen-activated protein kinases (MAPK) were also significantly activated by the o,p'-DDT-induced AP-1 and CRE activation. These results demonstrate that o,p'-DDT induced COX-2 expression via AP-1 and CRE activation through the PI3-K/Akt/ERK, JNK, and p38 MAP kinase pathways. These findings provide further insight into the signal transduction pathways involved in the carcinogenic effects of o,p'-DDT.

Effectiveness of malaria control during changing climate conditions in Eritrea, 1998-2003.

OBJECTIVE: To assess the effectiveness of impregnated mosquito nets, indoor residual spraying and larval control relative to the impacts of climate variability in the decline of malaria cases in Eritrea. METHODS: Monthly data on clinical malaria cases by subzoba (district) in three zobas (zones) of Eritrea for 1998-2003 were used in Poisson regression models to determine whether there is statistical evidence for reduction in cases by DDT, malathion, impregnated nets and larval control used over the period, while analysing the effects of satellite-derived climate variables in the same geographic areas. RESULTS: Both indoor residual spraying (with DDT or malathion) and impregnated nets were independently and significantly negatively associated with reduction in malaria cases, as was larval control in one zoba. Malaria cases were significantly positively related to differences in current and previous months' vegetation (NDVI) anomalies. The relationship to rainfall differences 2 and 3 months previously was also significant, but the direction of the effect varied by zoba. Standardized regression coefficients indicated a greater effect of climate in the zoba with less intense malaria transmission. CONCLUSION: The results support the view that both indoor residual spraying and impregnated nets have been independently effective against malaria, and that larval control was also effective in one area. Thus climate, while significant, is not the only explanation for the recent decline in malaria cases in Eritrea. If appropriate statistical approaches are used, routine surveillance data from cases attending health facilities can be useful for assessing control programme success and providing estimates of the effectiveness of individual control measures. Effectiveness estimates suitable for use in cost-effectiveness analysis have been obtained.

Mechanisms of interaction of endocrine-disrupting chemicals with glutamate-evoked secretion of gonadotropin-releasing hormone.

In previous studies, we detected a dichlorodiphenyltrichloroethane (DDT) derivative in the serum of children with sexual precocity after migration from developing countries. Recently, we reported that DDT stimulated pulsatile gonadotropin-releasing hormone (GnRH) secretion and sexual maturation in the female rat. The aim of this study was to delineate the mechanisms of interaction of endocrine-disrupting chemicals including DDT with GnRH secretion evoked by glutamate in vitro. Using hypothalamic explants obtained from 15-day-old female rats, estradiol (E2) and DDT caused a concentration-related increase in glutamate-evoked GnRH release while p,p'-dichlorodiphenyldichloroethene and methoxychlor had no effect. The effective DDT concentrations in vitro were consistent with the serum concentrations measured in vivo 5 days after exposure of immature rats to 10 mg/kg/day of o,p'-DDT. Bisphenol A induced some stimulatory effect, whereas no change was observed with 4-nonylphenol. The o,p'-DDT effects in vitro were prevented partially by a selective antagonist of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) subtype of glutamate receptors. A complete prevention of o,p'-DDT effects was caused by an estrogen receptor (ER) antagonist as well as an aryl hydrocarbon receptor (AHR) antagonist and inhibitors of protein kinases A and C and mitogen-activated kinases. While an intermittent incubation with E2 caused no change in amplification of the glutamate-evoked GnRH release for 4 h, continuous incubation with E2 or o,p'-DDT caused an increase of this amplification after 3.5 h of incubation. In summary, DDT amplifies the glutamate-evoked GnRH secretion in vitro through rapid and slow effects involving ER, AHR, and AMPA receptor mediation.

Parachuting cats and crushed eggs the controversy over the use of DDT to control malaria.

The use of DDT to control malaria has been a contentious practice for decades. This controversy centers on concerns over the ecological harm caused by DDT relative to the gains in public health from its use to prevent malaria. Given the World Health Organization's recent policy decisions concerning the use of DDT to control malaria, it is worth reviewing the historical context of DDT use. Ecological concerns focused on evidence that DDT ingestion by predatory birds resulted in eggs with shells so thin they were crushed by adult birds. In addition, DDT spraying to control malaria allegedly resulted in cats being poisoned in some areas, which led to increased rodent populations and, in turn, the parachuting of cats into the highlands of the island of Borneo to kill the rodents, a story that influenced the decision to ban DDT spraying. I focus on this story with the intention of grounding the current debate on lessons from the past.

Comparative performance of imagicides on Anopheles stephensi, main malaria vector in a malarious area, southern Iran.

BACKGROUND & OBJECTIVES: Jiroft district has subtropical climate and prone to seasonal malaria transmission with annual parasite index (API) 4.2 per 1000 in 2006. Anopheles stephensi Liston is a dominant malaria vector. The monitoring of insecticide susceptibility and irritability was conducted using discriminative dose as described by WHO. METHODS: The IV instar larvae were collected from different larval breeding places and transported to the temporary insectary, fed with Bemax and then 2-3 days-old emerged and sugar-fed adults were used for susceptibility and irritability tests employing WHO methods and kits to organochlorine (OC) and pyrethroid (PY) insecticides. RESULTS: Mortality rates of field strain of An. stephensi were 91.3 +/- 0.14 and 90 +/- 0.47% to DDT and dieldrin, respectively at one hour exposure time but was susceptible to all pyrethroids tested. The average number of take-offs per min per adult was 2.09 +/- 0.13 for DDT, 0.581 +/- 0.05 for dieldrin, 1.85 +/- 0.08 for permethrin, 1.87 +/- 0.21 for lambda-cyhalothrin, 1.53 +/- 0.13 for cyfluthrin, and 1.23 +/- 0.1 for deltamethrin. INTERPRETATION & CONCLUSION: Currently, deltamethrin is being used for indoor residual spraying against malaria vectors in the endemic areas of Iran. The findings revealed that the main malaria species is susceptible to all pyrethroids including deltamethrin, permethrin, cyfluthrin and lambda-cyhalothrin but was tolerant to DDT and dieldrin. This report and the finding are coincided with results of previous studies carried out during 1957-61 in the same area. Irritability tests to OC and PY insecticides revealed the moderate level of irritability to DDT compared to pyrethroids and dieldrin. Monitoring for possible cross-resistance between OC and PY insecticides should come into consideration for malaria control programme.