Behavioural and insecticidal effects of organophosphate-, carbamate- and pyrethroid-treated mosquito nets against African malaria vectors.

Three insecticides - the pyrethroid deltamethrin, the carbamate carbosulfan and the organophosphate chlorpyrifos-methyl - were tested on mosquito nets in experimental huts to determine their potential for introduction as malaria control measures. Their behavioural effects and efficacy were examined in Anopheles gambiae Giles s.s. (Diptera: Culicidae) and Anopheles funestus Giles s.s. in Muheza, Tanzania, and in Anopheles arabiensis Patton and Culex quinquefasciatus Say in Moshi, Tanzania. A standardized dosage of 25 mg/m(2) plus high dosages of carbosulfan (50 mg/m(2), 100 mg/m(2) and 200 mg/m(2)) and chlorpyrifos-methyl (100 mg/m(2)) were used to compare the three types of insecticide. At 25 mg/m(2), the rank order of the insecticides for insecticide-induced mortality in wild An. gambiae and An. funestus was, respectively, carbosulfan (88%, 86%) > deltamethrin (79%, 78%) > chlorpyrifos-methyl (35%, 53%). The rank order of the insecticides for blood-feeding inhibition (reduction in the number of blood-fed mosquitoes compared with control) in wild An. gambiae and An. funestus was deltamethrin > chlorpyrifos-methyl > carbosulfan. Carbosulfan was particularly toxic to endophilic anophelines at 200 mg/m(2), killing 100% of An. gambiae and 98% of An. funestus that entered the huts. It was less effective against the more exophilic An. arabiensis (67% mortality) and carbamate-resistant Cx quinquefasciatus (36% mortality). Carbosulfan deterred anophelines from entering huts, but did not deter carbamate-resistant Cx quinquefasciatus. Deltamethrin reduced the proportion of insects engaged in blood-feeding, probably as a consequence of contact irritancy, whereas carbosulfan seemed to provide personal protection through deterred entry or perhaps a spatial repellent action. Any deployment of carbosulfan as an individual treatment on nets should be carried out on a large scale to reduce the risk of diverting mosquitoes to unprotected individuals. Chlorpyrifos-methyl was inferior to deltamethrin in terms of mortality and blood-feeding inhibition and would be better deployed on a net in combination with a pyrethroid to control insecticide-resistant mosquitoes.

Larvicidal and mosquitocidal extracts, a coumarin, isoflavonoids and pterocarpans from Neorautanenia mitis.

The present study aimed to evaluate extracts and compounds from tubers of Neorautanenia mitis against the malaria- and filariasis-transmitting mosquitoes, Anopheles gambiae and Culex quinquefaciatus, respectively. The extracts exhibited activity against larvae of A. gambiae and C. quinquefaciatus mosquitoes, and were also active against adult A. gambiae mosquitoes. The active extracts yielded the coumarin derivative pachyrrhizine, the isoflavonoids neotenone and neorautanone, and the pterocarpans neoduline, nepseudin and 4-methoxyneoduline as the active constituents. The activity of the crude extracts was at about the same magnitude as that of the constituent natural products, the latter's efficacy being almost at the same level for all the isolated compounds. The mosquitocidal activities of the pure compounds were comparable to those of the standard mosquitocides deltamethrin and alphacypermethrin. These findings corroborate traditional insecticidal application of N. mitis and the results can be extended for the control of mosquitoes especially at breeding sites.

Patterns of malaria related mortality based on verbal autopsy in Muleba District, north-western Tanzania.

Reliable malaria related mortality data is important for planning appropriate interventions. However, there is scarce information on the pattern of malaria related mortality in epidemic prone districts of Tanzania. This study was carried out to determine malaria related mortality and establish its trend change over time in both epidemic and non-epidemic areas of Muleba District of north-western Tanzania. A verbal autopsy survey was conducted to obtain data on all deaths of individuals who died in six randomly selected villages from 1997 to 2006. Relatives of the deceased were interviewed using a standardized questionnaire. Communicable diseases accounted for about two thirds (61.9%) of deaths among > or =5 years individuals and 84.8% in < or =5 years. Non-communicable diseases accounted for 28.9% and 14.1% deaths in > or =5 years and < or =5 years, respectively. Malaria was the leading cause of deaths in all age groups (40.3%) and among children <5 years (73.8%). Infants accounted for about two third (64.5%) of all malaria related deaths in children <5 years. Peak of malaria proportional mortality was highest during malaria epidemics. Most of the malaria-related deaths in this group were among 1-12 months (64.5%) followed by 13-24 months (20.9%), and 25-59 months (14.8%). Cerebral malaria accounted for 18.9% (N=32) of death related to malaria in all age groups; 12.1% (17/141) were in under-five, 42.9% (6/14) were in 5-14 years and 64.3% (9/14) in 15-70 years old. More than half of malaria related deaths (61.0%) in <5 years children were associated with severe anaemia followed by diarrhoeal disease (24.1%), cerebral malaria (12.5%) and respiratory infection (8.5%) as common conditions. The majority of the deceased caretakers first sought treatment at health facilities within 24hr of the onset of illness. Significantly a higher proportion of caretakers of the underfives in the epidemic area sought treatment within 24hr than in non-epidemic area (39.3% vs. 18.5%; P = 0.0385). In conclusion, malaria accounts for majority of deaths in Muleba district, with substantial proportion being attributed to malaria epidemics.

Comparison of the Paracheck-Pf test with microscopy, for the confirmation of Plasmodium falciparum malaria in Tanzania.

Paracheck-Pf is a rapid, qualitative immuno-assay for the detection of Plasmodium falciparum-specific histidine-rich protein-2 in samples of human blood. The assay has now been evaluated, against the usual 'gold standard', microscopy, using blood samples from 1655 individuals in five districts of Tanzania, four of which experience frequent malaria outbreaks. The aim was to verify whether Paracheck-Pf could be a reliable tool for the confirmation of malaria outbreaks in such areas. The overall measurements of the assay's performance were good, with a sensitivity of 90.0%, a specificity of 96.6%, a positive predictive value of 88.9%, and a negative predictive value of 97.0% (with an estimated malaria prevalence of 23.3%). There was, however, marked variation between the study districts, the assay's performance being relatively poor where the test had been stored for 12 months at room temperature (23.5+/-3.5 degrees C). The assay was easy to perform in the field and could clearly be a valuable tool in remote areas and in emergency situations, such as the early detection of malaria outbreaks. The cost of the assay (U.S.$0.62/test at the time of the present study) is sufficiently low that its routine use in the confirmation of P. falciparum malaria might also be cost-effective, particularly in areas where there are no facilities for microscopy and/or where the first-line treatment of malaria is based on relatively expensive artemisinin-based combinations.