Anti-larval Measures Research Articles

An outbreak investigation of dengue in medical students and health care workers in a tertiary care hospital, Pune

Dengue is fast emerging mosquito borne viral disease. There was sudden outbreak of dengue cases among Medical students and Health Care Workers in tertiary care hospital from September to November 2019. Therefore, outbreak investigation carried out and corrective actions taken to halt the outbreak. Study Objectives are to investigate outbreak of dengue cases in medical students and Health Care Workers and to take corrective actions to halt the outbreak.The outbreak investigations of Dengue cases was done as 28 cases were admitted which includes medical students and Health Care Workers in tertiary care hospital from September to November 2019. A thorough search for breeding sites of Aedes mosquito was done in premises of hospital, college and residential area. 5 teams were made consisting of Sanitary Inspector, interns, resident doctors and lecturer. House to house surveys were done for container index in Resident quarters and employees quarters. Health education on prevention of dengue was given to Medical students and Health Care Workers including interns, resident doctors, undergraduate students. Antilarval measures like abating, fogging and spraying of oildone.The mean age was 27.2 years, ranged for 14-68 years. Males 15(53.5%) and Females 13(46.4%). Out of 28,12(42.8%) Undergraduate students, 9(32.1%) Resident doctors and 7(25%) employees. 22(78.5%) NS-1positivecases and 16(57.1%) IgM dengue positive cases. The most common symptom found in this was fever (100%). Thrombocytopenia was most common abnormal laboratory finding which was present in 22(79%) patients out of 28 patients. Out of 22 patients having thrombocytopenia, platelet transfusion was done to 4 patients. Mean duration of stay in the hospital was 4 days.With the corrective measures taken, no new case of dengue was notified in November 2019 among Medical Students and Health Care Workers.

The efficacy of Ximenia americana plant mediated silver nanoparticles against dengue vector mosquito larvae [Aedes (Stegomyia) aegypti (Linnaeus, 1762) (Diptera: Culicidae)

Nanotechnology is an emerging technology and day to day expanding its roots of knowledge to various branches of Science and fulfilling human conveniences. To manage vector populations, new tools have been emerging through nanotechnology. Nanoparticles possess peculiar toxicity mechanisms due to surface volume ratio, and this may actively contribute to their excellent larvicidal potential against Aedes aegypti mosquito. Dengue is a mosquito borne disease and making major public health issue worldwide. Aedes (Stegomyia) aegypti (Linnaeus, 1762) prefers to bread in artificial containers, and anti-larval measures with Ximenia americana L. (Olacaceae) leaf mediated silver nanoparticles (AgNPs) proves to be a potential substitute for the existing organophosphorus insecticides like temephos, malathion and fenthion etc., for mosquito control programme. Larvae were exposed to varying concentrations of plant extracts and synthesized silver nanoparticles for 24 hours. From the results, it was found that plant extracts showed moderate larvicidal effects (LC50 at 179.87 and LC90 at 376.77 ppm) but, the synthesized silver nanoparticles had found to be toxic to larvae at LC50 (0.63 ppm) and LC90 (1.20 ppm). This research highlighted that, the Ximenia americana leaf mediated AgNPs are an efficient and eco-friendly agents against Ae. aegypti mosquito, though the laboratory studies have shown the promising results, yet their efficacy in the field is to be tested for effective mosquito larval control.

High efficacy of microbial larvicides for malaria vectors control in the city of Yaounde Cameroon following a cluster randomized trial

The rapid expansion of insecticide resistance and outdoor malaria transmission are affecting the efficacy of current malaria control measures. In urban settings, where malaria transmission is focal and breeding habitats are few, fixed and findable, the addition of anti-larval control measures could be efficient for malaria vector control. But field evidences for this approach remains scarce. Here we provide findings of a randomized-control larviciding trial conducted in the city of Yaoundé that support the efficacy of this approach. A two arms random control trial design including 26 clusters of 2 to 4 km2 each (13 clusters in the intervention area and 13 in the non-intervention area) was used to assess larviciding efficacy. The microbial larvicide VectoMax combining Bacillus thuringiensis var israelensis (Bti) and Bacillus sphaericus in a single granule was applied every 2 weeks in all standing water collection points. The anopheline density collected using CDC light traps was used as the primary outcome, secondary outcomes included the entomological inoculation rate, breeding habitats with anopheline larvae, and larval density. Baseline entomological data collection was conducted for 17 months from March 2017 to July 2018 and the intervention lasted 26 months from September 2018 to November 2020. The intervention was associated with a reduction of 68% of adult anopheline biting density and of 79% of the entomological inoculation rate (OR 0.21; 95% CI 0.14–0.30, P < 0.0001). A reduction of 68.27% was recorded for indoor biting anophelines and 57.74% for outdoor biting anophelines. No impact on the composition of anopheline species was recorded. A reduction of over 35% of adult Culex biting densities was recorded. The study indicated high efficacy of larviciding for reducing malaria transmission intensity in the city of Yaoundé. Larviciding could be part of an integrated control approach for controlling malaria vectors and other mosquito species in the urban environment.

COVID-19 lockdown: impact assessment on Aedes larval indices, breeding habitats, effects on vector control programme and prevention of dengue outbreaks

Aedes aegypti (Linn.) and Aedes albopictus (Skuse) are widespread vector mosquitoes responsible for the transmission of various disease-causing viruses to human including dengue virus (DENV). India is endemic for dengue disease and both of these vector mosquitoes are well established throughout India. Since, Aedes mosquitoes breeds in containers, WHO recommends to do a regular immature surveillance and implement appropriate control measures. Owing to the current COVID-19 pandemic, most of the countries have implemented continuous shutdown/lockdown, which affected the routine Aedes surveillance and vector control measures. In India, the first nation-wide lockdown was implemented on 24th, March 2020. As of now, Government of India has extended the lockdown till 30th, June 2020. In the present study, two rounds of Aedes surveillance was carried out in two localities of Bengaluru City (urban) of Karnataka State, India during the COVID-19 lockdown days and results were compared with pre-lockdown surveillance data to assess the impact of lockdown on Aedes larval indices, breeding habitats and dengue vector control programme. The recorded house index (HI) and Breteau index (BI) were 6.6 and 9.3 in K.P. Agrahara and 4.0 and 5.3 in Palace Guttahalli during pre-lockdown survey. The house index (HI) and Breteau index (BI) were found to be increased to 26.6 and 34.6 in K.P. Agrahara and 21.3 and 28.0 in Palace Guttahalli during the COVID-19 lockdown second survey. Aedes immature density has drastically increased in both the localities due to temporarily discontinued Aedes surveillance, larval control activities like source reduction and anti-larval measures during COVID-19 lockdown. The high indices show that the vector is increasing and this may result in higher dengue virus transmission. The results highly recommend to implement the Aedes vector control programme with limited health staffs following the physical distance and other protectives measures to prevent dengue outbreaks.

Clinical profile of Dengue fever in children of Nellore city, Andhra Pradesh, India

Background: India especially Andhra Pradesh is endemic for dengue, in dengue fever mortality and morbidity is more in children when compare to adults. Authors objective was to assess the clinical profile of the Dengue fever in children.Methods: Children below 14 years with serologically positive for dengue included in this study from June 2017 to June 2018, data was collected and analyzed with MS office 2016.Results: In 100 children 84 were suffering with Non Sever dengue , 16 were suffering with severe dengue. In the study population 68 were male children and 32 were female children, more children 68 were in the above 11 age group, 52 children stay in hospital for 3-6 days.Conclusions: Health education and anti-larval measures and anti-adult measures for mosquito control is effective measures.

Imported malaria: a possible threat to the elimination of malaria from Sri Lanka?

To discuss epidemiological aspects of imported malaria and the potential impact of imported malaria cases reported in Sri Lanka 2008-2011 in terms of a possible resurgence of the disease. The national malaria database was used to assess details regarding country where the infection was possibly acquired, species of Plasmodium, number of days lapsed between disembarkation in Sri Lanka and diagnosis, compliance with national treatment guidelines including percentage of patients followed up as per the national guidelines. After the strengthening of malaria surveillance, during the 4-year period, 152 imported malaria cases were recorded: an increase of 176% in the number of cases. Most of the imported malaria infections were acquired by Sri Lankan Nationals mainly from South Asia, especially India. Plasmodium vivax accounted for 64% of the infections. Approximately 50% of the cases were diagnosed in the Western Province. The average period from disembarkation in Sri Lanka to malaria diagnosis was 3.6days. Patients were managed and treated according to the national guidelines. 82% of the patients were followed up for 28days to ensure parasite clearance. There is a possible increasing risk of re-introduction of malaria to the country from imported cases. Enhanced surveillance activities and the increase in international travel have contributed to an increase in recorded case numbers. There is a need to further strengthen surveillance, especially for monitoring and timely addressing of imported malaria, if the country is to prevent the re-establishment of transmission within. The importance of having an efficient response mechanism to deal with imported malaria is also highlighted.

Integrated malaria vector control with microbial larvicides and insecticide-treated nets in western Kenya: a controlled trial

To assess the contributions of both microbial larvicides and insecticide-treated nets (ITNs) in terms of reducing malaria incidence in an integrated vector management programme in an area moderately endemic for malaria in the western Kenyan highlands. A pre-post, control group design was used. Larval and adult vector populations were surveyed weekly in six separate valley communities. The incidence of Plasmodium infections in children 6 months to 13 years of age was measured during the long and short rainy seasons each year. Baseline data were collected for 17 months, after which Bacillus-based larvicides were applied weekly to aquatic habitats in three of the valleys for another 19 months. At around the same time the larviciding was initiated, ITNs were introduced gradually into all study communities by the National Malaria Control Programme. The effect of larviciding, ITNs and other determinants of malaria risk was assessed by means of generalized estimating equations. The risk of acquiring new parasite infections in children was substantially and independently reduced by ITN use (odds ratio, OR: 0.69; 95% confidence interval, CI: 0.48-0.99) and larvicide application (OR: 0.44; 95% CI: 0.23-0.82), after adjusting for confounders. Vector control with microbial larvicides enhanced the malaria control achieved with ITNs alone. Anti-larval measures are a promising complement to ITN distribution in the economically important highland areas and similar transmission settings in Africa.

It all began with Ronald Ross: 100 years of malaria research and control in Sierra Leone (1899-1999).

It was in Sierra Leone, 100 years ago in 1899, that human malarial parasites were first observed in wild-caught Anopheles gambiae and An. funestus, the principal vectors of malaria in Africa. In the same year, Ronald Ross initiated the first antilarval measures for malaria control. This paper reviews 100 years of malaria field research and control in Sierra Leone, which became known as the 'White Man's Grave' in the 19th century largely because of the high malaria-related mortality amongst Europeans living there. The establishment of a field laboratory for the Liverpool School of Tropical Medicine in Freetown in 1920 made Sierra Leone the centre for malaria field research in Africa up to and during the Second World War. Eminent malariologists including Ronald Ross, Samuel Christophers, George Macdonald, Leonard Bruce-Chwatt, Brian Maegraith, Ian Macgregor, Brian Greenwood and Michael Service visited Sierra Leone for malaria-related activities. This review highlights the tremendous efforts made towards defining the epidemiological picture of the disease and the most effective means of combatting it. Malaria control in Sierra Leone, as in many other parts of the world, used to be based largely on mosquito eradication. However, experience gained over the past 100 years has shown that mosquito control is often not cost-effective in areas where the interruption of transmission cannot be sustained. Emphasis should now be on early diagnosis, treatment with effective antimalarials, and the selective use of preventive measures including vector control and insecticide-treated materials where they can be sustained.

6. Perspectives and constraints on chemotherapy and practical considerations in the use of vaccines: Analysis of available measures for malaria control in Africa south of the Sahara

Africa south of the Sahara is not homogeneous and presents several extreme conditions where malaria persistence is ensured by a complex and highly adaptable vector system. Plasmodium falciparum is the most widespread and life threatening of the malaria parasites of man, particularly for young children and pregnant women. Large-scale residual spraying was not totally effective and was very costly, and mass chemoprophylaxis was not feasible. The spread of chloroquine resistance added arguments against uncontrolled use of drugs. Chemoprophylaxis is now recommended only for pregnant women, especially in their first pregnancy, whilst chloroquine 25 mg base/kg over 3 days is recommended for curative treatment in villages. Second line treatment regimens should be available, together with the possibility of referring severe malaria cases quickly to appropriate clinical facilities. Other control measures include self-protection against mosquito bites by bednets (especially those impregnated with synthetic pyrethroids), mosquito coils, repellents, window and door screening; other measures to prevent manmosquito contact, such as careful siting of settlements and zooprophylaxis; anti-larval measures, i.e. source reduction, protection of wells and water reservoirs, larviciding, introduction of larvivorous fish; and sprays against adult mosquitoes. The elaboration of strategies for control and their application requires a study of the existing situation. A core of specialists is required in each country, to help with decentralized planning and evaluation of malaria control and to ensure quality control of services, training and applied field research. Additional measures may become available in the future, especially anti-malaria vaccines, and countries should be ready to study their application.

Anopheles gambiae complex and disease transmission in Africa

Anopheles gambiae complex mosquitoes are present throughout tropical Africa and its offshore islands. Recent work has shown that at least 6 cryptic or “sibling” species are involved. They comprise 2 salt-water species, A. melas and A. merus, 3 freshwater species—provisionally known as species A, B, and C, and a mineralwater species known as species D. Artificial inter-species crosses yield sterile hybrid males. Rarity of hybridization in nature proves the reproductive isolation and valid genetic barriers between these 6 species. Morphological identification of most individuals of both saltwater and the mineralwater species is possible for larvae and adult females, using meristic features and other variable dimensions and ratios. Differential identification of the 3 freshwater species relies almost completely on cytotaxonomic methods. Species A and B occur together in most areas, extending southwards to sub-tropical latitudes and eastward to Mauritius. Proportions of mixed A-B populations may depend directly or indirectly on relative humidity, with A favoured when nocturnal humidities approach saturation. Species B is often absent from areas of highest humidity, but thrives in relatively arid savannas and steppes. Species C and D have relict distributions. Both saltwater species are coastal: melas in West Africa and merus in East Africa and larger islands except Zanzibar; merus also spreads inland. Apart from species C, which is always zoophilic, all members of the complex are proven or probable vectors of human malaria and filariasis, but with some wide contrasts in their levels of vectorial efficiency. Transmission of some arboviruses (Tataguine, O'nyong-nyong) is associated with species B, and perhaps with A also. Species B may transmit setariasis of cattle; melas and merus may also carry enzootic filariae. Much of the confusing ecophenotypic plasticity of A. gambiae sensu lato is attributable to the differential biological characteristics of these 6 species with their dissimilar geographical distributions, behavioural contrasts and asynchronous population dynamics. Shifts in the species balance occur regularly between A and B and between freshwater and saltwater populations. Species C does not interchange so much with B under natural conditions, but may survive at high densities after control of A or B. Additional versatility is caused by genetic polymorphism in some of the species, notably B. This species is the most widespread, and individual females tend to be either endophilic or exophilic, anthropophagic or zoophagic, early biters or late biters, and doubtless other alternatives, according to the arrangement of their floating chromosome inversions. Control measures have to be considered separately for each of the sibling species. House spraying with residual insecticides against endophilic species A is possibly sufficient to break disease transmission (assuming favourable response of ancillary vectors) and even to eradicate A completely. Efficacy of this method against other species in the complex is reduced by their exophily, which can be enhanced by behaviouristic avoidance due to the extremely low threshold of irritability exhibited by gambiae s.l. adults in general. Genetic polymorphism of species B may lead to true behaviouristic resistance. Larvicidal control of species A and B is beneficial, but made operationally difficult by their tendency to utilize temporary breeding-sites. Effectiveness of DDT and cyclodiene insecticides is further limited by the development of physiological insecticide resistance by species A and B. Adequate control of both saltwater species, and probably the mineralwater species also, can be attained by antilarval measures. Prospects of reduction of malaria and filariasis where melas, merus and species A and D are principal vectors may be much better than many people imagine. Widespread prevalence and inherent resilience of species B represents an insurmountable public health obstacle at present. Continued research may provide new control methods for integrated use against these mosquitoes. Concepts such as seeding breeding sites with pathogenic microsporidians or fungi, releasing sterile hybrid males or chemosterilized males, and other even more elaborate genetic control techniques, may be of special relevance to control of gambiae complex mosquitoes and diseases they transmit.

Some entomological aspects of the malaria eradication pilot project in Malaya.

In 1960 a pilot project was started in Selangor, Malaysia, to investigate the feasibility of malaria eradication by means of house-spraying with DDT at 6-monthly intervals, and the distribution of an anti-malarial drug (combination of chloroquine and pyrimethamine) to the population at the time of spraying; this account covers the first five spraying cycles (up to December 1963). The project area is considered to be representative of the geographical, ethnological and malariological features of Malaya. Surveys determined 33 species of anopheline mosquitos in the area. Five of these, Anopheles campestris, A. letifer, A. maclIlatlls, A. sllndaiws and A. IImbrosus were accepted as malaria vectors in 1960, but A. umbroslIs is no longer considered as such. A. campestris and A. sllndaiclIs were found together along a coastal belt where the prespraying malaria parasite rate among children aged 6-9 years was 9.7%. Inland, A. letifer was common on the coastal plain, and A. maclllatlls was widely distributed in the foothills. But except around the small aborigine camps, breeding of A. maclllatus was under effective control by anti-larval measures. The overall parasite rate in the inland areas was 1.4%; among the aborigines it was 49.0%. House-spraying resulted in the apparent eradication of A. campestris, but not of other anopheline species. There was also evidence that malaria transmission was stopped throughout the project area by the end of the second cycle of spraying, although this may not have been a fair test of malaria eradication where A. maculatlls is concerned. Present findings suggest that A. letlfer is not a vector of human malaria, at least in this area. Possible explanations are that only certain members of an A. letifer group are vectors, or that an increase in livestock during recent years has led to a deviation of this partially zoophilic species away from man. Notes arc also included on natural malarial infections found in A. donaldi and A. 11mbroslIs, on the possible role of A. nigerrimus in malaria transmission, and on A. hodgkini. The results of insecticide susceptibility tests made on A. letifer, A. maculatus, A. slIndaiclIs and A. umbrosus indicate that these species are normally susceptible to both DDT and dieldrin.

The influence of a deep river valley system on the dispersal ofAedesmosquitos

The influence of a deep river valley system on the distribution of dispersingAedesmosquitos was studied during 1958–59 in the vicinity of Edmonton, Alberta, Canada. Mosquito breeding within an area extending two to three miles beyond the city limits was prevented by anti-larval measures, and almost the only remaining breeding places were situated on the plains several miles to the north-west and south-east, yet considerable numbers of mosquitos appeared every spring in that part of the city included in the valley-ravine system of the North Saskatchewan River. Previous work had suggested that mosquitos dispersing across the plains were collected by the valley-ravine system and entered the city by passing down the main valley. The present paper attempts to account for this directed dispersal in terms of the behaviour ofAedesmosquitos in response to certain physical factors in the environment. The species mainly concerned wereAedes cataphyllaDyar,A. fitchii(Felt &amp; Young),A. excrucians(Wlk.) andA. stimulans(Wlk.).The initiation of dispersal flight downwind across the plains at twilight was observed. This took place soon after emergence and was not prevented by moderate winds. It was shown experimentally that neither high wind speeds nor turbulence inhibited the flight of newly emergedAedesmosquitos, but that individuals several days old were reluctant to take flight in turbulent conditions. Since wind speeds on the plains were generally higher than those in the valleys, these reactions would tend to confine older mosquitos to the valleys while not preventing dispersal of newly emerged mosquitos across the plains.The direction of the initial dispersal flights from the breeding places was observed in mosquitos escaping from rearing cages. Take-off was characteristically into the wind, but re-orientation downwind took place when the mosquitos began to be blown backwards in flight. It was shown experimentally, by releasing mosquitos in the field when the wind was very light, that the preferred direction of flight uninfluenced by wind was towards the lowest part of the horizon, both on the plains and in the valley. This response would tend to cause mosquitos on the plain to fly into ravines and valleys, and thence down-stream within them. Dispersing mosquitos would thus tend to be held by any valleys or ravines in their path.Swarming was never observed near the pools from which the mosquitos emerged, but was mainly seen in the valley or on the edge of the valley and ravines. Swarming ofA. cataphyllatook place during the evenings after the initial dispersal. The swarms were predominantly male but mating occurred during swarming. A cohesive factor seemed to be involved in the behaviour of the swarms, and further dispersal also seemed to occur gregariously; the movement of large male swarms down the river valley was observed.By the application of optomotor theories of insect flight to previously published data on the flight speed and behaviour ofA. aegypti(L.) andA. punctor(Kby.), the relationships between wind speed and permissible heights of flight of these species upwind and downwind were calculated. These relationships were consistent with the observations on dispersal ofAedesmosquitos in the Edmonton area, and could largely explain the mechanism by means of which deep valleys attracted and held dispersing mosquitos.In contrast to the open plains, the wooded river valley provides a more favourable environment for adult mosquitos. The supply of nectar is greater, saturation deficiency and wind speeds are lower and less variable, and shaded resting sites are more abundant.Observations on mosquitos in chambers with either vertical or horizontal humidity gradients suggested that the behaviour ofAedesmosquitos is not greatly influenced by humidity.

Insect Control in Public Health

preface states that this book is a follow-up of small Handbook of Malaria Control written 1940 by R. Svensson. authors of present beautifully prepared volume are wellknown workers problems related to insect transmission of human diseases. material is well organized and indexed. A full quarter of text is devoted to nine appendixes describing a series of technics developed for modern use of insecticides. This reviewer is highly conscious of difficulty of covering broad field indicated title. He feels that strictly technical parts of this volume are excellent, but that over-all public health aspects have not been adequately presented. statement that the basic principles of malaria control dealt with that booklet (Handbook of Malaria Control) have not changed represents attitude of authors toward public health aspects of their problem. It is obvious that basic principles of malaria control have been radically altered during past 25 years. 1940, prevention of malaria was limited largely to certain urban, suburban, and village areas, based essentially on reduction over-all incidence of anopheline mosquitoes brought about by larvicides. There was at that time no economically feasible method for prevention of rural malaria throughout most of world. introduction of DDT and other residual insecticides has brought attack against malaria into home with result that, for first time, public health workers are able to think terms of prevention of malaria rural areas. Although under certain special conditions residual insecticide does result a considerable reduction of anopheline mosquitoes, this is not necessarily so. residual insecticide campaign is directed not against a mosquito as such, but against mosquito which feeds human habitations and becomes infected with malaria parasites. 1940, partial malaria control most accessible populations was objective of antimalaria measures; whereas 1962, World Health Organization spearheaded a campaign for eradication of malaria throughout world. introduction it is stated that In East Africa . . . residual spraying of village huts with DDT for control of malaria also exterminated Aedes aegypti, and in parts of Central and South America where yellow fever control by anti-larval measures had been operation for some years, house spraying with DDT, added to these measures, has reduced Aedes aegypti almost to point of extinction. As a matter of fact, eradication of aegypti has been program some South American countries since 1930's, and since 1947 there has been an official Pan American Health Organization program for eradication of Aedes aegypti throughout Western Hemisphere. This program antedates introduction of DDT. Since its introduction, DDT has been used very largely as a larvicide and as a perifocal spray, and except Mexico has not been used as a house spray for eradication of aegypti. section on yellow fever, statement The disease is usually trans-

Observations on Chironomidae at Khartoum

This paper deals mainly with species ofTanytarsus(CHIRONOMIDAE) at Khartoum, particularly the very commonT. lewisiFreeman. These midges are a serious pest there, usually between November and April, causing great annoyance by swarming in vast numbers around lights during the first few hours after sunset and thus interfering with work and pleasure in the riverain area. They are probably responsible for a considerable amount of asthma and other conditions due to allergy. Little information is available about the biology of CHIEONOMIDAE in Africa, so reference is made to the PalaearcticT. mancusWalker, to whichT. lewisiis closely related. Studies of Chironomids from the health point of view elsewhere have little relation to the Khartoum problem, but work onChaoborus(CULICIDAE) is of interest.The conditions under which these midges occur at Khartoum and the methods of study are described.At least 26 species of CHIRONOMIDAE, including four ofTanytarsus, occur at Khartoum. The respiratory organs of some pupae are figured, and a key, based on the characters of these organs, is given for some of the species.Observations on the biology of all stages are recorded, particularly on the vertical movements and drifting of larvae and pupae and the time of emergence. Many larvae and pupae drift downstream at night, andT. lewisiemerges mainly in the early morning.Some exploratory field trials of larvicides were carried out. The results were inconclusive, and the difficulty of assessing them is pointed out. Thorough control by anti-larval measures would be extremely difficult owing to the large size of the river and the drift of pupae from upstream. It is believed that it might be possible but prohibitively expensive, and would have to be repeated annually, perhaps throughout the midge season. Various protective measures are discussed. It is considered that riverside dwellers who can do so should move inland, and that a barrier of trees parallel to the river would protect houses away from the river front. People who must be near the river in the evening can achieve considerable protection by clearing some vegetation, fogging with insecticide, or using air-cleaning or air-conditioning equipment.

Salmonellae and Shigellae

Salmonellae and Shigellae Martin Frobisher CopyRight https://doi.org/10.2105/AJPH.44.6.827-a Published Online: August 29, 2011

Present status of mosquito resistance to insecticides.

SummarySeveral species of culicine mosquitoes, including Culex pipiens autogenicus, C. tarsalis, Aedes taeniorhynchus, A. sollicitans, A. nigromaculis, and A. dorsalis, have developed resistance to DDT in localized areas. This resistance is sufficiently high to make control measures with DDT impractical. Moreover, some of the species have developed resistance to substitute insecticides used for their control, including toxaphene, benzene hexachloride and aldrin.Resistance to DDT among natural populations of Anopheles mosquitoes has not yet been established, even though intensive control operations have been carried out for several years in many areas, but we have no assurance that insecticide-resistant strains of Anopheles cannot develop.It is my opnion that intensive and widespread application of DDT and other insecticides to both larval and adult culicine mosquitoes is the primary reason for the appearance of resistant strains in certain areas. Antilarval measures other than the use of insecticides and the application of antiadult measures to minimum size localized areas may prevent or delay the appearance of insecticide-resistant mosquitoes. Further research to develop new mosquito insecticides and an expanded program of basic studies on the resistance problem are needed.

Anopheline Threshold of Malaria Transmission Noted in Jamaica

Malaria control operations directed toward reducing adult vector densities by antilarval measures always pose the vexing question: To what density level must the adult mosquitoes be reduced in order that the hazard of malaria transmission will be negligible? Such level, of course, will vary for the several species of vector mosquitoes and will depend principally on the habits of each species, on the habits of the human population in the subject area, and on the cuirrent abundance of human malaria carriers. In Puerto Rico during World War II, experience indicated that few, if any, new cases of malaria are likely to be contracted by military personnel living in screened quarters if the density (number of mosquitoes caught per trap per night) of Anopheles albimanus Wied. does not rise above two in the intracantonment area (Henderson, 1945).1 While the present author was stationed at Fort Simonds, Jamaica, B. W. I., an opportunity was afforded for making observations on this relationship between the abundance of the local malaria vector, A. albimanus, and malaria transmission. These observations are discussed here. Only one case of malaria was contracted by military personnel while on the base during the 18-month period, March 1944 through September 1945. Before the onset of the disease, this infected individual had been on duty for about 3 hours at dawn and 3 hours at sunset each day for several weeks at a location near the boundary of the protected area. During this 18-month period, the combination of little rainfall and adequate malaria control activities, both on the military reservation and in the area adjacent to it, resulted in low population densities of A. albimanus, as well as of other mosquitoes. The index of A. albimanus abundance during this period did not rise above five per trap-night. As a result of this favorable situation, there was a relaxation of malaria discipline among both military and civilian personnel. Personal antimalarial measures, such as restricted activities outdoors after sunset, use of repellents, and use of mosquito bars, were not strictly enforced. In 1945 following this relatively dry 18 -month period, the fall rainy season began early, and during some weeks of September and October

Observations on Malaria in the Presence and Absence of Anopheles Gambiae in an Experimental Area (Cumbe) Ceará, Brazil 1

SummaryA malaria study of a small isolated community in Brazil was made during the year 1940 before and after the eradication of Anopheles gambiae from the area. The records for the first four months of 1940 showed a rising Anophales gambiae density, and among the human population rising parasite and spleen rates and increasing symptomatology with demand for medication. The eradication of Anopheles gambiae in May by combined antilarval and antimosquito measures was accompanied by a sudden drop in the parasite rate from 85.7 per cent to about 20 per cent by June and a gradual reduction in spleen rate from 64.4 per cent to about 10 per cent by September. Although children in the age groups 1 to 4 and 10 to 14 years showed somewhat higher infection rates there was on the whole little difference in parasite rate between the young and older age groups, confirming previous information that malaria had not been endemic in the area. No consistent difference in infection intensity or in species of plasmodium, or incidence of gametocytes could be demonstrated among the age groups. Although there were many more gametocyte carriers in the months “with gambiae” than in the months “without gambiae” the ratio of gametocyte carriers to cases of malaria was found to be comparable in both periods.The spleen rate, unlike the parasite rate, showed a distinct difference among age groups, the group over 40 years showing the lowest rate of splenic enlargement and children 1 to 14 years the highest rate. There was no correlation found between species of parasite and size of spleen.

The treatment of malaria in a hyperendemic zone

I have tried to take a realistic view of the problem of malaria in a hyperendemic zone and to show how it differs from endemic malaria. In hyperendemic conditions anti-larval measures could never solve this problem for the native and are probably undesirable. We should not interfere with infection for it is on this the evolution of immunity depends. In this respect the interests of the native might appear to clash with those of the immigrant but in reality it is not so for various reasons which we need not consider here. Future advances in the handling of hyperendemic malaria will probably be along the lines of improved technique in individual treatment. For the native, immunological considerations must determine the technique. In the case of the European, we must rely on continual treatment of a disease, which we cannot hope to prevent by sanitation or control by immunity.

Malaria in the Philippine Islands 1,2

IV. SummaryMalaria is a disease of great, although not of paramount, importance in the Philippine Islands. It is found chiefly in foothill regions, being transmitted principally by the funestus-minimus sub-group of mosquitoes, which tends to breed in small rivers or streams, or flowing ditches of clear, somewhat shaded, fresh water. There are seasonal variations due either to the drying up of streams or to such an increase in velocity or volume as to make mosquito breeding impossible. Hence, very wet or very dry seasons are not malarious. Flat lands and all areas above 2000 feet in altitude are not malarious. The low coastal plain is not malarious. In general, malaria in the Philippines is a disease of transitional seasons and transitional regions.As in all tropical regions, malaria control in the Philippines presents a serious economic problem. Probably not more than G$0.05 per capita per annum could be spent in the average small malarious community for control measures. Such measures will have to be continuous for this century and perhaps for the next. The tropics generally are poor in money but rich in time. Malaria control must be planned with this fact in mind and all available, feasible measures utilized. Anti-larval measures can not be omitted from any control program. Such measures, added to bed-nets and anti-malarial drugs should bring about results in time, provided a modest educational campaign and continued research is coincident with them. But in the Tropics no more permanence may be anticipated in malaria control than in road repairs or water-sterilization.