Extension of indoor residual spraying for malaria control into high transmission settings in Africa

Contrary to previous consensus, a recent WHO statement recommends a more dominant role for indoor residual spraying (IRS) in malaria control in high transmission settings of sub-Saharan Africa and re-emphasises the role of DDT. We review the issues related to this change in recommendation. In high transmission settings, IRS must be implemented indefinitely and at high quality to achieve control. As current infrastructure limitations and unpredictable funding make this unlikely, each country must carefully consider the role of IRS. There remains a need to support ongoing insecticide-treated net scale-up. Insecticide choice is hampered by the lack of economic costing data.     

An evaluation of the residual lifespan of DDT in malaria control

The insecticide lifespan of DDT was assessed in huts sprayed for malaria control. The age of the spray deposits ranged from 3 up to 22 months. Blood-fed female Anopheles arabiensis were either released into the huts or exposed on sprayed surfaces by a bioassay technique. Mosquitoes released were recovered in exit traps fitted on windows or dead on the floor. Only 50% or less of mosquitoes released in sprayed huts were recovered. Mortality figures for recovered mosquitoes ranged from 94% at 3 months, declining to 19% for huts sprayed 18 months previously. Of the recovered mosquitoes, 60% or more attempted to escape from sprayed huts within two hours postrelease up to 15 months postspray. Bioassays gave average mortalities of 95 and 76% on thatch and mud walls, respectively. Analysis of mud samples from test huts showed that target dose of 2 g AI/m2 of DDT was not being achieved. The results support the need for an annual spraying cycle.     

Effects of suspended residual spraying and of imported malaria on malaria control in the USA

The activities of the National Malaria Eradication Programme, a co-operative campaign inaugurated in July 1947 by the United States Public Health Service and certain State and local health agencies, are outlined. Control operations reached their maximal level in 1948, when 1,364,950 dwellings in 13 "malarious" States were sprayed with residual DDT, and the percentage of mosquito control achieved was 83.2.In 1950, only 2,227 cases of malaria were reported, as compared with 16,203 in 1947 and 9,797 in 1948. But the return of infected servicemen from Korea caused a temporary increase in the incidence in 1951 and 1952, when the totals were 5,600 and 7,023, respectively. In 1953, however, only 559 civilian cases were reported; of the cases appraised, 28 were of local origin, and, of these, at least 24 are known to have been infected in 1952.The Public Health Service ceased active participation in the Programme in 1951, but continued to give technical advice. At the same time, State authorities received Federal support in activating malaria surveillance-and-prevention programmes. More-selective anti-anopheline activities have replaced residual insecticide spraying, which is now carried out in only a few isolated areas. It is believed that these measures have prevented imported malaria from increasing the diminishing incidence of primary indigenous cases in the USA.     

Leishmaniasis in the Jordan Valley II. Sandflies and transmission in the central endemic area

Cutaneous leishmaniasis in the Jordan Valley is maintained within the close association of the rodent Psammomys obesus and sandfly Phlebotomus papatasi, which appear to be the exclusive host and vector species. The incidence of the disease was similar to the distribution of Psammomys colonies in the region, i.e., the plains of light stoneless soil. An infection rate of 93% was recorded in the very common P. obesus. Other potential host species, except for Mus musculus, were scarce and no infection with Leishmania was found in them. The only Phlebotomus species caught in significant numbers was Ph. papatasi and this was also the only species harbouring leishmanial parasites, up to 56% in one sample.All Leishmania isolates from Psammomys and from Ph. papatasi were identical to those from local human cases.The density of Ph. papatasi populations in uncultivated areas was correlated with soil conditions favouring high humidity in Psammomys burrows.A very low rate of engorged females among the Sergentomyia species collected suggests that the common species, S. antennata and S. africana asiatica, are highly autogenous.     

Effect of indoor residual spraying of DDT and bendiocarb on the feeding patterns of Anopheles pseudopunctipennis in Mexico

Intense and persistent use of DDT for malaria control has increased resistance and induced exophilic behavior of Anopheles pseudopunctipennis. An evaluation of bendiocarb and DDT to control this species in Sinaloa, Mexico, showed that, in spite of DDT-resistance, both insecticides produced similar effects. Feeding patterns were analyzed to explain these results. Resting mosquitoes were collected over the dry and wet seasons. Anophelines were tested in an ELISA to determine the source of the meals. The human blood index (HBI) ranged from 3.3 to 6.8% in DDT- and from 12.7 to 26.9% in bendiocarb-sprayed houses. Irritability and repellency in DDT-sprayed houses could explain the reduced HBI. In contrast, bendiocarb produced higher mortality. These effects could have affected different components of the vectorial capacity and similarly reduced malaria.     

Pesticide Residues in Soil from the Jordan Valley,Jordan

Bulletin of Environmental Contamination and Toxicology - The presence of pesticide residues in soil is a matter of serious concern as many compounds have been shown to produce adverse effects....     

Cost-effectiveness of malaria control interventions when malaria mortality is low: insecticide-treated nets versus in-house residual spraying in India

Malaria is one of the leading causes of morbidity and mortality in the developing world and a major public health problem in India. Disillusioned by in-house residual spraying (IRS), and increasingly aware that insecticide-treated nets (ITNs) have proved to be effective in reducing malaria mortality and morbidity in various epidemiological settings, policy-makers in India are keen to identify which is the more cost-effective malaria control intervention. A community randomised controlled trial was set up in Surat to compare the effectiveness and efficiency of IRS and ITNs. Both control strategies were shown to be effective in preventing malaria over the base-case scenario of early diagnosis and prompt treatment. The mean costs per case averted for ITNs was statistically significantly lower (Rs. 1848, 1567-2209; US$ 52) than IRS (Rs. 3121, 2386-4177, US$ 87). The incremental cost-effectiveness ratio for ITNs over IRS was Rs. 799 (US$ 22). The conclusions were robust to changes in assumptions. This study expands the scope of recent comparative economic evaluations of ITNs and IRS, since it was carried out in a low mortality malaria endemic area.     

Group-based citizenship in the acceptance of indoor residual spraying (IRS) for malaria control in Mozambique

In 2006, the Mozambican Ministry of Health expanded its existing Indoor Residual Spraying (IRS) programme into Manhiça District in the south of the country. Widespread household coverage is required to have a significant impact on malaria transmission, making acceptability fundamental to success. Between 2006 and 2008 we conducted anthropological research in order to understand acceptability of IRS in the context of the implementation process, policy debates, local and regional politics and historical processes. In the first phase of this qualitative study, conducted between January and April 2006, 73 interviews and 12 focus groups were conducted with key stakeholders from 14 locales in and around the town of Manhiça: householders, community leaders, health care professionals, sprayers, and District officials. Analysis revealed IRS to be broadly acceptable despite very low levels of perceived efficacy and duration of effect. In contrast to previous studies which have linked acceptance to a reduction in mosquitoes, nuisance biting and malaria, we found people's compliance with the programme to be founded on a sense of group-based citizenship. The involvement of local governmental leaders in the intervention appears to have led many to accept spraying as part of their civic duty, as decreed by post-war decentralisation policy in rural areas. We discuss the implications of this ‘passive’ form of compliance for the acceptability and sustainability of malaria control and other public health programmes.     

Impact of DDT indoor residual spraying on Phlebotomus argentipes in a kala-azar endemic village in eastern Uttar Pradesh.

Data on the operational efficacy of DDT indoor residual spraying against Phlebotomus argentipes, the vector of kala-azar in India, are scarce. We therefore undertook a study of the impact on kala-azar and its vector of DDT indoor residual spraying in the Varanasi district of eastern Uttar Pradesh. Preliminary results indicate that after two rounds of DDT spraying in one village no P. argentipes were found during the peak vector season; in contrast, a large number of these sandfies were collected in the unsprayed comparison village.     

Assessment of nonoccupational exposure to DDT in the tropics and the north: relevance of uptake via inhalation from indoor residual spraying

Background

People who live in dwellings treated with indoor residual spraying (IRS) of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] for disease–vector control in the tropics and indigenous populations in the Arctic who comsume marine mammals experience high nonoccupational exposure to DDT. Although the use of DDT in IRS is rising, the resulting nonoccupational exposure is poorly characterized.

Objectives

We have provided a comparative assessment of exposure to DDT and its metabolites in the general population of the tropical and northern regions and in highly exposed populations in these regions.

Methods

We compiled > 600 average or median DDT concentrations from the peer-reviewed literature, representing > 23,000 individual measurements in humans, food, air, soil, and dust. We use Monte Carlo sampling of distributions based on these data to estimate distributions of population- and route-specific uptake. We evaluate our exposure estimates by comparing them with biomonitoring data.

Results

DDT concentrations are highest in people living in IRS-treated houses and lowest in the northern general population, differing by a factor of about 60. Inuits and the general population in the tropics have similar concentrations. Inhalation exposure explains most of the difference in concentration between the highly exposed and the general population in the Tropics. Calculated exposure levels are consistent with human biomonitoring data.

Conclusions

Nonoccupational inhalation exposure is a relevant exposure pathway for people living in homes treated by IRS of DDT. Continued monitoring of time trends and DDE to DDT ratios in the Tropics and in the North is needed to identify a possible slowdown in concentration decline and the influence of ongoing DDT use.     

超低容量喷雾和滞留喷洒杀灭蚊虫的现场实验

目的探讨超低容量喷雾和滞留喷洒在杀灭蚊虫中搭配使用的效果。方法应用车载超低容量喷雾、烟雾机进行超低容量喷雾,普通喷雾器进行滞留喷洒,不同灭蚊方式单独或综合运用,在喷药前后对蚊虫密度采用动物帐诱法、诱蚊灯法和人工小时法进行监测,确定不同喷药方法的灭蚊效果。结果滞留喷洒可降低室内蚊虫密度,但对室外蚊虫活动无明显影响;超低容量喷雾也可降低室内蚊虫密度,但室外诱蚊灯法监测的蚊虫密度通常会增高,动物帐诱法监测的蚊密度会降低。结论同时使用滞留喷洒和超低容量喷雾,可以提高蚊虫控制效果;羊帐诱法是评价超低容量喷雾现场灭蚊效果较好的方法。     

Reduced efficacy of insecticide-treated nets and indoor residual spraying for malaria control in pyrethroid resistance area, Benin

The pyrethroid knockdown resistance gene (kdr) has become widespread in Anopheles gambiae in West Africa. A trial to test the continuing efficacy of insecticide-treated nets (ITN) and indoor residual spraying (IRS) was undertaken in experimental huts at 2 sites in Benin, the first where kdr is present at high frequency (Ladji), the second-where An. gambiae is susceptible (Malanville). Holes were made in the nets to mimic worn nets. At Malanville, 96% of susceptible An. gambiae were inhibited from blood-feeding, whereas at Ladji feeding was uninhibited by ITNs. The mortality rate of An. gambiae in ITN huts was 98% in Malanville but only 30% at Ladji. The efficacy of IRS was equally compromised. Mosquitoes at Ladji had higher oxidase and esterase activity than in a laboratory-susceptible strain, but this fact did not seem to contribute to resistance. Pyrethroid resistance in An. gambiae appears to threaten the future of ITN and IRS in Benin.     

DDT and malaria prevention: addressing the paradox

Background

The debate regarding dichlorodiphenyltrichloroethane (DDT) in malaria prevention and human health is polarized and can be classified into three positions: anti-DDT, centrist-DDT, pro-DDT.

Objective

We attempted to arrive at a synthesis by matching a series of questions on the use of DDT for indoor residual spraying (IRS) with literature and insights, and to identify options and opportunities.

Discussion

Overall, community health is significantly improved through all available malaria control measures, which include IRS with DDT. Is DDT “good”? Yes, because it has saved many lives. Is DDT safe as used in IRS? Recent publications have increasingly raised concerns about the health implications of DDT. Therefore, an unqualified statement that DDT used in IRS is safe is untenable. Are inhabitants and applicators exposed? Yes, and to high levels. Should DDT be used? The fact that DDT is “good” because it saves lives, and “not safe” because it has health and environmental consequences, raises ethical issues. The evidence of adverse human health effects due to DDT is mounting. However, under certain circumstances, malaria control using DDT cannot yet be halted. Therefore, the continued use of DDT poses a paradox recognized by a centrist-DDT position. At the very least, it is now time to invoke precaution. Precautionary actions could include use and exposure reduction.

Conclusions

There are situations where DDT will provide the best achievable health benefit, but maintaining that DDT is safe ignores the cumulative indications of many studies. In such situations, addressing the paradox from a centrist-DDT position and invoking precaution will help design choices for healthier lives.     

Exposure of spray-men to dieldrin in residual spraying

A study of the exposure of spray-men to dieldrin was made in a pilot scheme of residual spraying in the Taveta-Pare area of East Africa. A detailed work study was completed on the operators, and sources of contamination were enumerated. Filter paper pads were placed on the skin and outside clothing and the pick-up was estimated chemically. A spray-man, while using the daily average of 2.12 kg (4.7 pounds) of dieldrin and observing the protective measures laid down, received a dermal exposure of 1.8 mg of dieldrin per kg of body-weight per day. This was possibly reduced somewhat by washing with soap and water upon completion of each day''s work. The sixteen spray-men and assistants were exposed for 180 days per year and there was an interim period of 2 months between spray cycles. No clinical symptoms of poisoning were observed.