Chief Vector Research Articles

Aspergillus flavus (Link) toxins reduces the fitness of dengue vector Aedes aegypti (Linn.) and their non-target toxicity against aquatic predator

Mosquito that accountable for dispersal of dengue fever is Aedes aegypti Linn. and considered to be a chief vector for dengue especially in South Asian countries. Aspergillus flavus is considered to be wild growing green yellow colonies and synthesis highly regulating aflatoxins (B1, B2, G1 and G2) as a secondary metabolite. Mycotoxins of A. flavus showed its efficacy against III and IV instars of Ae. aegypti with more than 90% mortality at the prominent dosage of 2 × 108 conidia/ml. The proximate lethal concentrations (LC50 and LC90) of mycotoxins against third and fourth instars was 2 × 105 and 2 × 107 respectively. Correspondingly, sub-lethal dosage of mycotoxin A. flavus significantly inhibited the level of α- β-carboxylesterase and SOD activity and upregulated the level of major detoxifying enzymes GST and CYP450. Moreover, sub-lethal dosage also showed higher deterrent and fecundity effects. Gut-histological examination reveals that the A. flavus considerably affected the gut epithelial cells along with the inner gut lumen as compared to the control. The non-target screening of A. flavus against two aquatic predators (A. bouvieri and Tx. splendens) display more than 80% of mortality rate against both the species at the dosage of 2 × 1016 (two-fold-higher dosage used in larval assays). Thus the biosafety assessment suggests that A. flavus display higher toxicity against the non-targets and it is not-recommended to apply it directly to the aquatic habitat of dengue mosquito which shares their living space with other beneficial insects.

Anti-diuretic action of a CAPA neuropeptide against a subset of diuretic hormones in the disease vector Aedes aegypti.

The mosquito Aedes aegypti is a vector responsible for transmitting various pathogens to humans, and their prominence as chief vectors of human disease is largely due to their anthropophilic blood feeding behaviour. Larval stage mosquitoes must deal with the potential dilution of their haemolymph in freshwater, whereas the haematophagus A. aegypti female faces the challenge of excess ion and water intake after a blood meal. The excretory system, composed of the Malpighian tubules (MTs) and hindgut, is strictly controlled by neuroendocrine factors, responsible for the regulation of diuresis across all developmental stages. The highly studied insect MTs are influenced by a variety of diuretic hormones and, in some insects, anti-diuretic factors. In the present study, we investigated the effects of AedaeCAPA-1 neuropeptide on larval and adult female A. aegypti MTs stimulated with various diuretic factors including serotonin (5-HT), a corticotropin-related factor (CRF) diuretic peptide, a calcitonin-related diuretic hormone (DH31) and a kinin-related diuretic peptide. Overall, our findings establish that AedaeCAPA-1 specifically inhibits secretion of larval and adult MTs stimulated by 5-HT and DH31, whilst having no activity on MTs stimulated by other diuretic factors. Furthermore, although AedaeCAPA-1 acts as an anti-diuretic, it does not influence the relative proportions of cations transported by adult MTs, thus maintaining the kaliuretic activity of 5-HT and natriuretic activity of DH31 In addition, we tested the effects of the second messenger cGMP in adult MTs. We established that cGMP has similar effects to AedaeCAPA-1, strongly inhibiting 5-HT- and DH31-stimulated fluid secretion, but with only minor effects on CRF-stimulated diuresis. Interestingly, although AedaeCAPA-1 has no inhibitory activity on kinin-stimulated fluid secretion, cGMP strongly inhibited fluid secretion by this diuretic hormone, which targets stellate cells specifically. Collectively, these results support that AedaeCAPA-1 inhibits select diuretic factors acting on the principal cells and this probably involves cGMP as a second messenger. Kinin-stimulated diuresis, which targets stellate cells, is also inhibited by cGMP, suggesting that another anti-diuretic factor in addition to AedaeCAPA-1 exists and may utilize cGMP as a second messenger.

MOSQUITO IDENTIFICATION AND MOLECULAR XENOMONITORING OF LYMPHATIC FILARIASIS IN SELECTED ENDEMIC AREAS IN GIZA AND QUALIOUBIYA GOVERNORATES, EGYPT.

Lymphatic filariasis is a vector-borne health problem that has been focally endemic in Egypt for centuries. The chief vectors of transmission are Culicinae species. Control measures in the form of mass drug administration of DEC citrate treatment have been implemented in Nile delta for almost a decade. This study aimed to identify the prevalent mosquito species in endemic areas in Giza and Qualioubiya governorates and to monitor Wuchereria bancrofti infection by detecting the parasite DNA in collected mosquitoes. Adult mosquitoes were collected using light traps hung indoors. Microscopic examination was performed to identify and examine the morphologic characters of mosquitoes. Female Culex mosquitoes were subjected to semi-nested PCR to detect filarial DNA targeting repetitive DNA sequences (pWbl2 repetitive region) specific for W. bancrofti. The results revealed 3 species of mosquitoes Culex pipiens, Culex pusillus and Culex quinquefasciatus with the predominance of Culex pipiens (85.7%). Wuchereria bancrofti DNA was not detected in any of the collected mosquito pools. With progress of elimination programme in Nile Delta, follow up studies with larger sample size are recommended as the predominance of Culex pipiens the main lymphatic filariasis vector remains a risk of transmission in such areas.

“AIDS is rape!” gender and sexuality in children's responses to HIV and AIDS

This paper examines young African school children's understanding of HIV and AIDS. Based on focus group interviews with children aged 7-8 in KwaZulu-Natal province, South Africa, it explores the ways in which gender and sexuality feature in their responses to the disease. Data were collected between 2003 and 2004 through 26 focus groups involving 55 boys and 64 girls. The paper argues that younger children are active agents in giving meaning to the disease. Their agency is negotiated within complex social processes involving sexual violence, highly unequal gender/age inequalities, but also sexual expression. Those expressions are subsumed however under a regime of violence and fear catapulting men, albeit with contestation, as chief vectors in the spread of the disease and a source of girls' anxieties. Children's responses to the disease are the effects of material, symbolic and discursive forces effectively constraining the opportunities available to them and creating patterns of vulnerability especially for young girls. Interventions aimed at scaling up efforts to address young children responses to the disease must be situated in parallel efforts to end poverty, sexual violence and pervasive gender inequalities in order to foster more comprehensively the exercise of young children's agency.

Climate‐driven range extension of a sea urchin: inferring future trends by analysis of recent population dynamics

AbstractPatterns of climate‐forced range shift in the marine environment are informed by investigating the population dynamics of an ecologically important sea urchin (Centrostephanus rodgersii– Diadematidae) across its newly extended range in Tasmania (southeastern Australia). A growth model of C. rodgersii is developed allowing estimation of a sea urchin age profile and, in combination with abundance data, we correlate the sea urchin population dynamic with respect to environmental signals across the range extension region. Growth patterns did not vary across the extension region; however, there was a strong pattern of decreasing sea urchin age with increasing distance from the historic range. The sequential poleward discovery of the sea urchin, a pattern of declining age and a general poleward reduction in abundance along the eastern Tasmanian coastline are consistent with a model of range extension driven by recent change in patterns of larval dispersal. We explore this hypothesis by correlating C. rodgersii population characteristics with respect to the East Australian Current (EAC), i.e. the chief vector for poleward larval dispersal, and reveal patterns of declining sea urchin age and abundance with increasing distance from this oceanic feature. Furthermore, C. rodgersii is generally limited to sites where average winter temperatures are warmer than the cold threshold for its larval development. Potential dispersal and physiological mechanisms defining the range extension appear to be strongly coupled to the EAC which has undergone recent poleward advance and resulted in coastal warming in eastern Tasmania. Predicted climate change conditions for this region will favour continued population expansion of C. rodgersii not only via atmospheric‐forced ocean warming, but also via ongoing intensification of the EAC driving continued poleward supply of larvae and heat.

Rural Development and Malaria Control in Sub-Saharan Africa

The rapidly expanding population of Sub-Saharan Africa has led to an increased demand for land in which to live and grow food. The process of rural development continues to change the physical landscape, increasing mosquito breeding and biting rates of the chief vector of malaria in Africa, Anopheles gambiae, a mosquito exquisitely adapted for exploiting people. At the same time, development alters the social environment, affecting wealth, inequality, household entitlements, and male and female workloads, which lead to changes in coping and caring strategies. Despite the fact that malaria is sensitive to changes in the physical and social environment, most control tools use only chemicals (antimalarials and insecticides), not biophysical environmental modifications nor strengthening social systems. While antimalarials and insecticides are extremely effective weapons, they are probably not sustainable in the long term due to the emergence of resistant organisms. Here we suggest that environmental and social management should be considered as part of the suite of interventions against malaria, since these are likely to be effective in specific settings and represent a sustainable approach to malaria control in rural Africa.

Rapid PCR detection of the methicillin resistance gene, mecA, on the hands of medical and non-medical personnel and healthy children and on surfaces in a neonatal intensive care unit.

The hands of medical personnel are the chief vectors for transmission of antibiotic-resistant bacteria and probably serve as an important reservoir for antibiotic resistance genes in hospitals. In this survey we examined different reservoirs of the methicillin resistance gene, mecA, using a simplified PCR method. Samples (n = 151) were taken from the hands of medical and non-medical personnel and healthy children and from surfaces in a neonatal intensive care unit (NICU). We also performed sampling from 4 different body sites in 5 of the medical personnel. Fifteen out of 16 nurses (94%) from the ICU carried the mecA gene on their hands, whereas only 35% of the paediatric nurses were mecA-positive. Of all medical personnel, 44% carried the mecA gene on their hands. There was a significant difference (p < 0.015) between medical and non-medical personnel in terms of the carriage rate of mecA. Four samples from surfaces in a NICU--2 ventilators, 1 bench and 1 telephone--were positive for mecA. Our results are comparable with those from previous studies on reservoirs of methicillin-resistant coagulase-negative staphylococci using conventional culture techniques.

Spiders and Borrelia burgdorferi: no evidence of reservoir occurrence in central Arkansas

Although Ixodes ticks are considered the chief vector for Borrelia burgdorferi in the USA, B. burgdorferi has also been identified in mosquitoes, horse flies, and deer flies. We examined the possibility of these organisms being harbored in two species of spider in central Arkansas. Ten wolf spiders (Lycosa gulosa) and two brown recluse spiders (Loxosceles reclusa) were collected in central Arkansas during early summer and fixed in formalin. Paraffin-embedded sections of the spiders were examined for spirochetes using the modified Steiner spirochete staining method and examined for B. burgdorferi using immunohistochemistry. All 12 spiders from both species were found to be negative for all spirochetes including B. burgdorferi. Spiders in our sample appeared not to harbor B. burgdorferi. Further studies utilizing larger sample sizes, more sensitive testing measures, or spiders from an area more endemic with B. burgdorferi may further prove or disprove that spiders are capable of harboring this organism.

Anopheline mosquitoes and malaria parasites in Taiwan.

Extensive taxonomic studies of the genus Anopheles were carried out in Taiwan during the first half of the 20th century. As a result, 17 species of Anopheles were identified and reported as occurring in Taiwan. However, the occurrence of two species, An. kochi and An. fluviatilis, in Taiwan is doubtful. Vector competence of the anophelines of Taiwan was also studied both in the laboratory and in the field during the same period of time, and experimental infections of 8 species of Anopheles were carried out by Anazawa in the 1920s. The results showed that all species tested were susceptible to three human plasmodia except for An. sinensis which was refractory to Plasmodium falciparum. The results of dissection of nearly 10,000 anopheline mosquitoes collected from the field by various workers suggested that An. minimus is the chief vector in Taiwan. Crithidial flagellates resembling malaria sporozoites were found in the salivary glands of 4 common species of Anopheles collected from cow-stables. These flagellates may have been misidentified as malaria sporozoites in the earlier investigations. During the first part of the operations for malaria control and eradication, anopheline mosquitoes were collected by day from 1,118 houses scattered over the island. Of the 25,656 specimens of Anopheles collected, nearly 80% were An. minimus, mostly from bedrooms. Since the highly anthropophilic and endophilic An. minimus was determined to be the chief vector of malaria in Taiwan, DDT was applied to the wall surfaces in houses for malaria control and eradication. Before spraying DDT, the rate of P. malariae infections was very high in areas where malaria is endemic. However, these infections were more quickly suppressed by DDT spraying than two other parasite species. Other details of studies on the ecology and behavior of anophelines are also presented.

Cache Valley virus: experimental infection in Culiseta inornata

Experiments were conducted to examine the dynamics of Cache Valley virus in Culiseta inornata, the probable chief vector of the virus. Of about 1500 laboratory reared C. inornata exposed to viraemic suckling mice, 72 took a blood meal. A relatively high precentage (93%) of the latter mosquitoes became infected. The virus increased more than 100-fold in the experimentally infected mosquitoes. The increasing viral titres were noticed after 7 days and after 15 days. Peak titres averaged 105.0 (mean suckling mouse intracerebral lethal dose) SMICLD50/0.02 mL. The infected mosquitoes had peak titres until at least 35 days after the mosquitoes ingested blood from infected suckling mice. A single trasmission of virus by bite occurred 30 days after the viraemic blood meal. Transovarial transmission was demonstrated. In two experiments, 3.3 and 2.9% of infected mosquitoes transovarially transmitted Cache Valley virus to both male and female progeny. The minimum infection rate for the progeny was 2.05/1000 mosquitoes. This is the first reported experimental demonstration of transovarian transmission in a species of mosquito which overwinters as an adult. The role of transovarian transmission in the natural maintenance of Cache Valley virus remains undetermined.

Zoological evidence to the origin of flood-waters and their role in vector distribution

The study of the flood-waters revealed that the breach of irrigation channels due to heavy downpour, triggered the floods, as the first flood-waters largely contained characteristic riverine fauna. Later on, the riverine fauna was outnumbered by pond fauna indicating the overflow from ponds, adding to the amount of flood-waters. The flood-waters play a significant role in the distribution of animals in general and vectors in particular. The chief vectors included Cyclops, Lymnaea, Planorbis and five genera of fishes. Pockets of stagnant flood-water provide a breeding ground for mosquitoes to create a future nuisance. The faunal study of flood-waters offers a proof to their origin, which otherwise requires a manual survey.

The Rift Valley fever epizootic in Egypt 1977–1978 2. Ecological and entomological studies

Epidemiological factors related to the introduction, spread and maintenance of Rift Valley fever (RVF) virus were studied during the 1977–1978 epizootic in Egypt. Culex pipiens is the most ubiquitous and prevalent mosquito species in the Nile Valley and Delta. Isolation of RVF virus from unengorged C. pipiens, and demonstration of laboratory transmission of the virus by this species, strongly implicate it as the chief vector in Egypt. Virus transmission to man also occurs by contamination when handling infected meat and by inhaling natural virus aerosols. Wild rodents apparently do not serve as RVF virus reservoirs. Domestic sheep, cattle, buffaloes, camels, goats, donkeys and dogs act as amplifying hosts. Over 30% of the camels sampled at the southern border of Egypt were serologically positive for antibodies to RVF virus and it appears likely that the virus was introduced into Egypt, either by these animals or by other vehicles from the south.

Eradication of Culex pipiens fatigans through cytoplasmic incompatibility.

Culex pipiens fatigans is the chief vector of filariasis in south-east Asia. Urbanization has often caused the numbers of this mosquito—and with it the danger of filariasis infection—to increase alarmingly1. The natural vigour, tolerance and fast development of resistance to insecticides of this mosquito necessitate the development of other control methods, and cytoplasmic incompatibility2 seems to be an ideal means.

Leishmaniasis in the Sudan Republic. 10. Natural infections in rodents.

SummaryInfections identical with Leishmania donovani on the basis of appearance in culture and pathogenesis in hamsters were recovered from 2 rodents, Rattus rattus and Acomys spp., trapped in Malakal town, Upper Nile Province. It appears that a rodent-sandfly-rodent cycle of leishmaniasis occurs in this town, but that in the absence of man-biting sandflies, humans do not become infected in this urban center.In Paloich District, approximately 100 miles north of Malakal, 2 definite and 2 equivocal Leishmania infections were found among 117 Nile Grass Rats (Arvicanthis niloticus luctuosus), out of a total of 242 wild rodents from this district. Three were isolated by hamster inoculation and one (equivocal) by direct culture of spleen tissue. These animals were trapped in an area where human kala-azar is endemic and in the same spots in Acacia forests where Phlebotomus orientalis was found to bite man and to be commonly infected with Leishmania. One person assisting in trapping sandflies and rodents in Paloich District subsequently developed a severe case of kala-azar. In Paloich District, leishmaniasis may be a true zoonosis, with A. niloticus luctuosus as a vertebrate reservoir and P. orientalis as the chief vector to humans.

Filariasis in Malaya—A general review

1. 1) At the outbreak of World War II, Brugia malayi was known to cause endemic filariasis in rural areas of Malaya, and a microfilaria resembling B. malayi had been found in macaque monkeys. W. bancrofti infections had been seen only in immigrants, and were thought to have been imported. Post-war investigations have changed this picture considerably. 2. 2) A number of small foci of periodic W. bancrofti infection have been discovered, one urban and several rural. In one rural area the vector was an anopheline, and the parasite developed poorly in local Culex fatigans, which however was a good host for an urban strain of W. bancrofti from Singapore. 3. 3) Two forms of B. malayi have been recognized in man. The periodic form is transmitted chiefly by the open-swamp species of Mansonia and by some anophelines; although not confirmed as a natural infection in animals, it can be transmitted to them experimentally. This form of B. malayi appears to be the common one in other parts of Asia. The chief vectors of the semi-periodic form are the swamp-forest Mansonia, and natural infections in animals are common; transmission from man to animal is relatively easy, and in parts of Malaya this form almost certainly behaves as a zoonosis. In the same areas animal infections with another Brugia, B. pahangi, are common; although not recognized as a natural infection in man, it has been transmitted to him experimentally. This situation has not yet been observed in other countries of Asia. 4. 4) Charts illustrate infection rates by age and sex, and the usual site of elephantiasis, the relationship between infection rate and microfilaria density, and the results of control measures. Despite very high microfilaria rates in young children of both sexes, females in the semi-periodic B. malayi area showed a much lower infection rate than males from the age of 10 years onwards. Repeated surveys in untreated populations showed the importance of natural fluctuations in incidence, but also showed that many people could live for years in highly endemic areas and remain apparently free from infection. 5. 5) Control was based largely on once-weekly doses of 5 mg. diethylcarbamazine citrate/kg./body wt. given for 6 weeks. Results were better and more lasting where the periodic B. malayi was prevalent and no animal infections were known. 6. 6) The broader significance of these findings is discussed and possible lines of investigation are suggested.

Disinfection of the hands of surgeons and nurses.

The hands of the nurse and the surgeon are undoubtedly two of the chief vectors of hospital infection. They often carry pathogenic organisms, in particular Staphylococcus aurelus, which may be present in large numbers. Price (1938) has shown that scrubbing with soap and water for six minutes will reduce the numbers Df bacteria on the hands by only about 50'. Devenish and Miles (1939) and others have found that about 30', of the rubber gloves worn at operations become punctured without the surgeon's knowledge, and bacteria can readily escape through the small holes which appear. Though these facts about hand scrubbing and gloves are quite well known, additional safeguards against manual contamination of wounds are not often used by surgeons ; nurses, for their part, are generally not expected to do anything more to control their hand flora than washing with soap and water after certain ward duties. Various antiseptics have been found to reduce the numbers of bacteria on the hands. Hexachlorophane soap (Traub, Newhall, and Fuller, 1944; Seastone, 1947) and phisohex (Hufnagel, Walter, and Howard, 1948) have been used for some years by surgeons in the United States, and a British paper in support of the latter has recently appeared (Smylie, Webster, and Bruce, 1959). Price (1951) has stressed the limitations of hexachlorophane soap when used irregularly, and finds that a conventional scrub with soap and water followed by three minutes' rinse in 70') alcohol before putting on gloves is more effective. The regular use of a hand cream containing chlorhexidine has been found to reduce the skin flora (Murray and Calman, 1955; Laurell, 1959), and its use by nurses in surgical and obstetric wards has been associated with some reduction in the incidence of cross-infection (Cook, Parrish, and Shooter, 1958; Gillespie, Simpson, and Tozer, 1958). In this paper we describe experiments on the relative merits of several pre-operative antiseptic applications to the surgeon's hands, with particular reference to the numbers of bacteria emerging through holes in gloves. We also describe a study on the routine use of hexachlorophane soap and some other methods by nurses working in accident and burns wards.

A survey of rats trapped in the wellington area for ectoparasites and organisms of the salmonella, pasteurella, and leptospiral groups

Abstract Extract It has long been established that rats can play an important part in the transference of infectious diseases to man. With this fact in mind, the late Dr J. H. Blakelock, former Director of the National Health Institute, Wellington, began a survey of the rat population in the Wellington district and of rats brought to the area by overseas ships. This work has been continued, the trapped rats being examined for the presence of Xenopsylla cheopis, a flea known to be the chief vector of plague, for Pasteurella pestis, the causative organism of plague, for organisms of the Salmonella group, and for evidence of leptospiral infection.

Identity of the Black Fly That Attacks Ducklings and Goslings in Canada (Diptera: Simuliidae)

For many years, the black fly Simulium venustum Say has been considered to be the chief vector of Leucocytozoon simondi M. &amp; L. (=L. anatis Wick.), a protozoan parasite infesting the bloodstream of ducks and geese and causing a malarialike disease that is usually fatal to immature birds. The organism undergoes part of its life-cycle in the stomach of the fly, which transmits it, through its bite, to the primary host. Its development in the latter results in the rupture of blood cells, with extensive destruction of tissue of the spleen, liver, and other organs. Although, superficially, the case against S. venustum appears to be already proved, recent studies of this species in Eastern Canada have indicated that some aspects of its supposed relation to L. simondi cannot readily be explained on the basis of what is known of its life-history and habits. My attention was focussed on this problem when I discovered in 1953 that the Simulium species reported by Walker (1927) as causing wholesale deaths in a flock of goslings at Fredericton, N.B., was neither Simulium bracteatum Coq. (a synonym of S. (Eusimulium) aureum Fries), as reported by Walker, nor S. venustum Say, as suggested by Twinn (1933).

Incidence of tularemia and Rocky Mountain spotted fever among common ticks of Arkansas.

SummaryIn the course of a year's field study in Arkansas, 576 pools totalling 28,661 lone star ticks (Amblyomma americanum) were tested for tularemia by animal inoculation, and 11 pools (1.9 per cent) were found positive—an average of one infected tick in 2,605, assuming only one infected individual to each positive pool. The distribution of naturally infected ticks was shown to be spotty, and the finding of a batch of infected, unfed larvae of A. americanum indicates the probable occurrence of transovarian passage of tularemia in this species.The lone star tick was the only arthropod found naturally infected with tularemia, although the number of other ticks tested was insufficient to justify general conclusions. Tularemia-infected lone star ticks were collected in May, July, and September, coinciding with the reported seasonal incidence of human infections; and the data presented, taken in connection with previous epidemiologic investigations, point to ticks as the chief vectors of tularemia in Arkansas.Pools of lone star, American dog, black-legged and rabbit ticks were tested by animal inoculation for Rocky Mountain spotted fever organisms (R. rickettsi), but only one successful isolation was made, from the tissues of a guinea pig inoculated from a pool of female American dog ticks. Reactions of several guinea pigs inoculated with material from pools of lone star ticks indicated rickettsial infections, but the organism was not recovered from the test animals.

The control of malaria in Borneo (An account of the Tambunan experiment)

1. (1) In previous work, Anopheles maculatus was exonerated, and “ Anopheles leucosphyrus” was incriminated as the chief vector of malaria in Borneo (as it would appear to be throughout a considerable part of the East). 2. (2) Based on this work, the Tambunan Experiment was carried out in North Borneo from 1949 to 1952, to determine whether the admission of sunlight to seepages, followed if possible by cultivation to render it permanent, eradicated not only the vector but the malaria which it carries. 3. (3) An area of about 10 square miles of particularly difficult jungle-covered hills was selected, in which spleen rates had been maintained at over 80 per cent. for at least 14 years. In this area, jungle was cleared over all seepages, numbering about 200, and involving about 32 miles of waterway. 4. (4) There was an immediate 95 per cent. reduction of vector breeding. This was maintained throughout the 3 years without significant further work. 5. (5) There was a fall in spleen rates during the 1st year, from 86 per cent. to 56 per cent. This fall was continued during the subsequent years to 53 and 45 per cent respectively. 6. (6) There was some malaria transmission remaining, as shown by parasites in the blood of some young babies.This was possibly due to infiltration of infected mosquitoes from surrounding uncontrolled highly malarious villages. 7. (7) In a Comparison Area, the spleen rate, maintained at 100 per cent. at every examination during the previous 14 years, was still 100 per cent. during the first 2 years of the experiment while conditions remained the same. 8. (8) During the final 2 years of the Experiment this spleen rate fell unexpectedly, and for the first time on record children were found without evidence of malaria. This was found to be due almost certainly to the enthusiasm of a new Village Headman who had distributed drugs to the children, and had imitated the methods carried out in the Experimental Area. 9. (9) It is considered very desirable that measures should be undertaken over a larger area, on the scale of an actual campaign, to eliminate infiltration of infected mosquitoes, to test other means of clearing such as the use of selective herbicides, and as the next justifiable step in the conquest of malaria in those lands where “ A. leucosphyrus” is the vector. 10. (10) It is believed that the Tambunan Experiment has shown this method of malaria control to be effective, relatively permanent, and able to be applied by the people themselves, to the advantage of their agriculture and to the economic development of the land.