Focal Spraying Research Articles

Validation of the Early Warning and Response System (EWARS) for dengue outbreaks: Evidence from the national vector control program in Mexico.

BackgroundDuring 2017, twenty health districts (locations) implemented a dengue outbreak Early Warning and Response System (EWARS) in Mexico, which processes epidemiological, meteorological and entomological alarm indicators to predict dengue outbreaks and triggers early response activities.Out of the 20 priority districts where more than one fifth of all national disease transmission in Mexico occur, eleven districts were purposely selected and analyzed. Nine districts presented outbreak alarms by EWARS but without subsequent outbreaks (“non-outbreak districts”) and two presented alarms with subsequent dengue outbreaks (“outbreak districts”). This evaluation study assesses and compares the impact of alarm-informed response activities and the consequences of failing a timely and adequate response across the outbreak groups.MethodsFive indicators of dengue outbreak response (larval control, entomological studies with water container interventions, focal spraying and indoor residual spraying) were quantitatively analyzed across two groups (”outbreak districts” and “non-outbreak districts”). However, for quality control purposes, only qualitative concluding remarks were derived from the fifth response indicator (fogging).ResultsThe average coverage of vector control responses was significantly higher in non-outbreak districts and across all four indicators. In the “outbreak districts” the response activities started late and were of much lower intensity compared to “non-outbreak districts”. Vector control teams at districts-level demonstrated diverse levels of compliance with local guidelines for ‘initial’, ‘early’ and ‘late’ responses to outbreak alarms, which could potentially explain the different outcomes observed following the outbreak alarms.ConclusionFailing timely and adequate response of alarm signals generated by EWARS showed to negatively impact the disease outbreak control process. On the other hand, districts with adequate and timely response guided by alarm signals demonstrated successful records of outbreak prevention. This study presents important operational scenarios when failing or successding EWARS but warrants investigating the effectiveness and cost-effectiveness of EWARS using a more robust designs.

A 5-year review of malaria surveillance in Kuching, Sarawak

Introduction: Malaria is endemic in Sarawak contributing to the highest incidence rate in Malaysia. Kuching division consists of three main areas, namely Kuching district, Lundu and Bau. This review aims to highlight the trends of malaria over the past five years in terms of demographic characteristics and vector control programmes and to identify factors that contribute to the difficulty in malaria control programme in this state. Materials and Methods: This is a descriptive review of malaria cases based on surveillance data compiled from 2000 to 2004. Data is analysed based on demographic background, malaria species, type of malaria infection and vector control activities between the three districts. Results: Lundu has the highest average 5-year incidence rate per 10,000 population of 121.97 as compared to the national figure of 4.10. Malaria is more prevalent in males (14.3%) than females (5.7%). Among the race, Dayaks had the highest prevalence rate (66.5%). Peak age affected is between 15 to 40 years. The predominant species was Plasmodium vivax (65.4%) followed by Plasmodium falciparum (32.8%). For occupation, the majority of cases were among villagers (55.2%) followed by foreign workers (19.0%). Cases were detected mainly by passive case detection (82.7%) and blood film for malarial parasites was positive in 2.67%. For malaria control activities, focal spraying were successfully done in 94.4% of the structures, regular spraying in 89.5% structures, impregnated bednet distribution among 38.2% population and mass drug administration distributed among 80.7% of the population. Conclusion: Results analysis has shown that the incidence rate of malaria in Kuching division is very high, particularly in Lundu district. Although activities conducted by the malaria control programme is sufficient, it has not been able to successfully reduce the incidence of malaria in this region. Problems identified include difficulty in accessing the affected areas, movements of illegal immigrants, financial constraints and lack of training of field staff involved in malaria control. Recommendations include integrating malaria control measures with cross border agents, community participation, aggressive surveillance programmes and improvement of vector control.

Eco-bio-social determinants of dengue vector breeding: a multicountry study in urban and periurban Asia

To study dengue vector breeding patterns under a variety of conditions in public and private spaces; to explore the ecological, biological and social (eco-bio-social) factors involved in vector breeding and viral transmission, and to define the main implications for vector control. In each of six Asian cities or periurban areas, a team randomly selected urban clusters for conducting standardized household surveys, neighbourhood background surveys and entomological surveys. They collected information on vector breeding sites, people's knowledge, attitudes and practices surrounding dengue, and the characteristics of the study areas. All premises were inspected; larval indices were used to quantify vector breeding sites, and pupal counts were used to identify productive water container types and as a proxy measure for adult vector abundance. The most productive vector breeding sites were outdoor water containers, particularly if uncovered, beneath shrubbery and unused for at least one week. Peridomestic and intradomestic areas were much more important for pupal production than commercial and public spaces other than schools and religious facilities. A complex but non-significant association was found between water supply and pupal counts, and lack of waste disposal services was associated with higher vector abundance in only one site. Greater knowledge about dengue and its transmission was associated with lower mosquito breeding and production. Vector control measures (mainly larviciding in one site) substantially reduced larval and pupal counts and "pushed" mosquito breeding to alternative containers. Vector breeding and the production of adult Aedes aegypti are influenced by a complex interplay of factors. Thus, to achieve effective vector management, a public health response beyond routine larviciding or focal spraying is essential.

INDOOR RESIDUAL SPRAYING OF DDT FOR MALARIA CONTROL

We wish to comment on O'Shaughnessy's article1 on the use of DDT to control malaria from our years of malaria eradication experience.2 From 1948 to 1958, H. H. C. participated in Taiwan's malaria program. In 1950, there were 1.2 million cases of malaria out of a population of 7.5 million.3,4 After a period of DDT indoor residual spraying from 1953 to 1957,3,5–7 the number of cases dropped to 533. Subsequent surveillance, case detection, treatment, and focal indoor residual spraying resulted in only 19 cases in 1965 (out of a population of 12.4 million) and the World Health Organization (WHO) declared that malaria has been eradicated on the island. Remarkably, the total program cost per capita from 1953 to 1957 was NT $3 (US $0.10 at the current exchange rate).6 The story of parachuting cats into malaria-infested areas to counteract the increasing rodent populations after the DDT spraying program killed the native cats is cited as a parable of ecosystem meddling and has become an urban legend. In Taiwan, we knew indoor residual spraying killed cats and other animals, so we asked villagers to keep them out of the house for several days after the spraying. Surveillance of 682 houses sprayed (264 with cats) found that 43 cats died, along with many mice and chickens.3 Some animals died in a day, suggesting that direct toxicity was the issue, not biomagnification. We are skeptical about the validity of the reports of cats being parachuted into Sarawak in 1960. An airdrop of DDT supplies in 1954 during the pilot project is mentioned in another source,8 but supplies were always transported via speedboats during H. H.C.'s tenure as the malaria advisory team leader in Sarawak from 1962 to 1968. Colbourne et al. never mentioned parachuting cats to us or in their article, which focused on the Sarawak malaria epidemic from 1955 to 1958.9 Similarly, we heard no mention of such an incident from the WHO Senior Malaria Advisor from 1959 to 1961. In Sarawak, Malaysia, we heard complaints about spoiled thatch roofs of farm huts10 in the neighboring area of Sabah (North Borneo), but never Sarawak. Longhouses—the typical indigenous abode in Sarawak at the time—have roofs of billian (extremely hard wood impervious to moth larvae)8; thatching was not used so longhouses were unaffected. Despite claims to the contrary, we do not believe that there were any major typhus epidemics or outbreaks of sylvatic plague in Sarawak due to increased vector populations. In fact, in Taiwan, we experienced a positive consequence of the spraying program: head lice disappeared. Today's reader might cringe, but villagers often asked to have their heads sprayed with DDT! Indoor residual spraying is controversial, but it is appealing for a variety of reasons. It contaminates the environment less than larviciding or aerial spraying. It is economical. Spraying can be done once or twice a year for 3 to 5 years followed by focal spraying. Malaria eradication has failed for multiple reasons: drug resistance, continuous mosquito exposure, geographical challenges, and political instability. Although restarting indoor residual spraying alone is insufficient to control malaria, fears of environmental destruction are overblown. It is time to retire the cat story and reconsider DDT's role in the fight against malaria.

Tratamentos focais e totais com inseticidas de ação residual para o controle de Triatoma brasiliensis e Triatoma pseudomaculata no Nordeste brasileiro

To efficiently control the triatomines Triatoma brasiliensis and Triatoma pseudomaculata, a field trial was performed to compare conventional versus focal spraying of deltamethrin 5% SC at 25 mg a. i./m2 and the slow-release organophosphate malathion 8.3% SR at 2g a. i./m2. The assay took place in the county of Boa Viagem, Ceará State, with 1541 households, randomly separated into 4 groups. Two of them received focal spraying: PT, treated with deltamethrin indoors and in the peridomicile, and PL, which received slow-release malathion in the same circumstances. The other groups received conventional, i.e., total application: PT with deltamethrin in the intra- and peridomicile, and PL, which was treated with deltamethrin indoors and slow-release malathion in the peridomicile. Entomological surveys at 6 and 12 months post-treatment showed better results for mixed treatment, the PL group, probably due to good indoor performance for the pyrethroid and better performance of the slow-release formulation under the hostile peridomiciliary conditions. Domestic animal shelters underwent numerous modifications over the course of the year, fostering reduced insecticide performance in the peridomicile.