Adulticidal Activity of Olea vera, Linum usitatissimum and Piper nigera against Anopheles stephensi and Aedes aegypti under Laboratory Conditions.

BACKGROUND: There are several plant extractions which are being used for mosquito control. The aim of this study was to evaluate the efficacy of Olea vera, Linum usitatissimum and Piper nigera against Anopheles stephensi and Aedes aegypti under laboratory conditions. METHODS: These tests were carried out using WHO recommended bioassay method for adult mosquitoes. RESULTS: The extracts from black pepper was more effective as adulticide with lowest LC(50) values (2.26% and 8.4%) against Aedes aegypti and Anopheles stephensi after 24 h of exposure while after 48h (1.56% and 5.11%) respectively. In terms of LC(90) value black pepper was best with (8.66% and 30.1%) against Ae. aegypti and An. stephensi after 24 h of exposure while after 48h (4.59% and 17.3%) respectively. In terms of LT(50) black pepper took 15 h to kill 50% tested population of Ae. aegypti while against An. stephensi it took more than 2 days. In terms of percentage mortality black pepper kill 84% of the population of Ae. aegypti and 44.75% of the An. stephensi population. CONCLUSION: Black pepper showed best results in term of LC(50), LC(90), LT(50) and percentage mortality against Ae. aegypti and An. stephensi. Our study suggested that the plant extracts have potential to kill adult mosquitoes, are environment friendly and can be used for the control of mosquitoes.

Launching the first postgraduate diploma in medical entomology and disease vector control in Pakistan.

The Health Services Academy has launched a 12-month postgraduate diploma course in medical entomology and disease vector control. The objective is to create a core of experts trained to prevent and control vector-borne diseases. The course is a response to the serious health and socioeconomic burden caused by a number of vector-borne diseases in Pakistan. The persistence, emergence and re-emergence of these diseases is mainly attributed to the scarcity of trained vector-control experts. The training course attempts to fill the gap in trained manpower and thus reduce the morbidity and mortality due to these diseases, resulting in incremental gains to public health. This paper aims to outline the steps taken to establish the course and the perceived challenges to be addressed in order to sustain its future implementation.

Launching the first postgraduate diploma in medical entomology and disease vector control in Pakistan

The Health Services Academy has launched a 12-month postgraduate diploma course in medical entomology and disease vector control. The objective is to create a core of experts trained to prevent and control vector-borne diseases. The course is a response to the serious health and socioeconomic burden caused by a number of vector-borne diseases in Pakistan. The persistence, emergence and re-emergence of these diseases is mainly attributed to the scarcity of trained vector-control experts. The training course attempts to fill the gap in trained manpower and thus reduce the morbidity and mortality due to these diseases, resulting in incremental gains to public health. This paper aims to outline the steps taken to establish the course and the perceived challenges to be addressed in order to sustain its future implementation

The role of vectors in emerging and re-emerging diseases in the Eastern Mediterranean Region

Considerable attention has recently been drawn at a global level to the serious threat to humans by the new, emerging and re-emerging infectious diseases. Among the infectious vector-borne diseases, dengue, dengue haemorrhagic fever, yellow fever, plague, malaria, leishmaniasis, rodent-borne viruses and arboviruses are considered to be persisting, and sometimes re-emerging, with serious threats to human health. In the Eastern Mediterranean Region, dengue, malaria and leishmaniasis are the significant vector-borne diseases. This article discusses the role of vectors in the re-emergence of malaria, leishmaniasis and dengue fever and their control

Inheritance of DDT dehydrochlorination and of a mechanism restricting uptake of DDT in the mosquito Aedes aegypti.

Crosses and backcrosses were made between the T8 dichlorodiphenyltrichloroethane (DDT) resistant strain and NS susceptible strain. Each generation was tested for resistance, for internal levels of DDT and dichlorodiphenyldichloroethylene (DDE) (thus "DDT uptake" (DDT + DDE) and percentage DDT dehydrochlorination in vivo), and for DDT dehydrochlorination in vitro, both at the larval and adult stages. The patterns of inheritance of uptake and dehydrochlorination were different. At both life stages, dehydrochlorination (both in vivo and in vitro) was intermediate in the F1, reverting to or exceeding the parental strains in the backcrosses except in adult tests on the backcrosses to the susceptible strain where it remained intermediate. Uptake increased very substantially in the F1 compared with either parental strain and was also high in the backcrosses. This was interpreted as being due to the disruption of an uptake-restricting mechanism in T8 brought about by outcrossing. Larval resistance in the various generations was correlated significantly with dehydrochlorination, both in vivo and in vitro but bore no clear relation to uptake. Resistance in adults was found not to be correlated significantly with either.

Effect of selection for dichlorodiphenyltrichloroethane (DDT) resistance on the uptake and breakdown of DDT in Aedes aegypti L.

Aedes aegypti larvae and adults were selected to high levels of resistance with dichlorodiphenyltrichloroethane (DDT) along separate lines. The larval-selected line showed three responses associated with larval resistance: increased detoxication of DDT by dehydrochlorination to dichlorodiphenyldichloroethane DDE (demonstrated both in vivo and in vitro), increased tolerance to unmetabolised ("residual") DDT and, a reduction in uptake of DDT. Larval selection caused very little change in adult resistance or the uptake of DDT by adults, but there was an increase in dehydrochlorination. In the adult-selected line dehydrochlorination was increased by selection and was significantly correlated with resistance.

A point survey of periurban and urban malaria in Karachi.

A point survey of malaria in Karachi revealed a concentration of malaria cases in the periurban perimeter and marginal areas where immigrating groups, including Afghan refugees and Biharis from Bangladesh are concentrated. Populations of Anopheles stephensi, Karachi's main vector, were low, and were feeding chiefly on buffaloes which are also concentrated along the periurban perimeter. Maintenance of malaria transmission in periurban zones may depend on immigration of susceptibles, bovid hosts which help maintain zoophilic vector populations, and mosquito breeding sites in water tanks or buffalo hoofprints. The vector's switch to man-biting behaviour may occur either due to a 'spillover' effect from buffalo corrals to surrounding houses, or when buffaloes become less available for biting. Four types of chromosome inversions were found in the Karachi An. stephensi; as this species is not a vector in similar habitats in Lahore and Pondicherry where such inversions are not prevalent, it is likely that its status as a vector is related to chromosomal polymorphism influencing behaviour.

Field measurement of the effective dominance of an insecticide resistance in anopheline mosquitos.

Anopheles culicifacies that were susceptible, heterozygous, or homozygous resistant to HCH and dieldrin were differentially marked with fluorescent dusts and released twice weekly into village huts in Pakistan that had been sprayed with four different dosages of HCH to see which of the genotypes died and which survived. The three highest dosages killed all three genotypes in the first four weeks, and heterozygotes and susceptibles for at least 12 weeks. The lowest dosage killed all the susceptibles throughout the period, and all but 0.07% of the heterzygotes. Thus the resistance is effectively recessive at the higher dosages and unlikely to be selected rapidly, as long as the gene frequency is low to start with and the houses are sprayed regularly. Similar releases of partially and completely resistant A. stephensi, and completely resistant A. subpictus, showed greater survival rates on exposure to the high HCH dosages than the same genotypes of A. culicifacies.

Status of insecticide resistance in anopheline mosquitoes of Punjab Province, Pakistan.

Susceptibilities of six anopheline mosquito species from nine localities in Punjab Province to DDT, dieldrin, malathion, fenitrothion, fenthion and propoxur were determined. DDT-resistance was found in An. annularis, An. culicifacies, An. stephensi and An. subpictus but An. nigerrimus and An. pulcherrimus were susceptible to DDT. Association between DDT-resistance and endophilic habit of the mosquitoes has been observed but needs further confirmation. Dieldrin resistance was present in all the six species. Five species were susceptible to malathion, and only An. stephensi showed incipient malathion resistance without cross resistance to other organophosphates. The six species were susceptible to fenitrothion and propoxur. An. nigerriums and An. subpictus showed some evidence of resistance to fenthion, the remaining four species were fenthion-susceptible.

Selection for DDT-susceptibility in Anopheles culicifacies from Lahore, Pakistan.

Two colonized and three wild strains of Anopheles culicifacies were screened to isolate a DDT-susceptible colony. No susceptible strain was isolated, as the colonies tested were either homozygous or nearly so for resistance. A more rigorous selection of a highly DDT-resistant strain suggested the involvement of ancillary factors in addition to major genes for DDT-resistance in the species.