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Adolpho Lutz and the origins of medical entomology in Brazil.

Adolpho Lutz (1855-1940) formed a bridge between the Bahian Tropicalist School and post-Mansonian medicine. Before taking over as head of the São Paulo Bacteriological Institute (1893), Lutz traveled through a variety of regions and delved into various disciplines. In the 1880s, he was already arguing that leprosy was transmitted by mosquitoes. Carbuncles, cholera, and typhoid fever were then the accepted models for investigating the etiology of infectious diseases. Following the discovery of how malaria was transmitted, attention turned to hematophagous diptera. Physicians, bacteriologists, zoologists, and veterinarians reshaped the network of actors involved in the 'hunt' for the agents and transmitters of diseases, as they began relying on analogies with malaria and yellow fever. Edwin Ray Lankester, director of the British Museum (Natural History), launched then a worldwide investigation into species that might be linked to human disease. The species described by Lutz and his proposed classification system were vital to Frederick Theobald's fundamental work in medical entomology, published in the early twentieth century. In 1908, Lutz brought with him to the Oswaldo Cruz Institute a remarkable quantity of research and experiments in all branches of the newly created "tropical medicine," devoted especially to entomology.

Animals↗

Malaria vectorial capacity of a population of Anopheles gambiae: an exercise in epidemiological entomology.

In order to assess the factors of malaria vectorial capacity and the daily reproduction rate, separate consideration is given to data from Kankiya, Northern Nigeria, concerning the incidence of vector-man contact (the man-biting rate), the vector's expectation of infective life, as reflected by the proportion of parous mosquitos under certain conditions, and the vector's man-biting habit, comprising the frequency of feeding and the human blood index. The main difficulty in the assessment of each of these factors was shown to be that of representative and adequate sampling, especially in a sprayed area. In order to compensate for deficiencies in the Kankiya data, especially with regard to the daily and cyclic survival-rates, the gonotrophic cycle and the effective sporogonic period, more complete published data on an Anopheles gambiae population in East Africa were examined, and extrapolations were made from these data in spite of the consequential risks involved.The results of the analysis show that the spraying of an area with DDT reduced the malaria vectorial capacity of Anopheles gambiae sp. B (the main vector of Plasmodium falciparum in the area) by an over-all factor of about 23 times. Nevertheless the basic reproduction rate of the disease is estimated to have averaged slightly over 20 in the sprayed area during the 6 months of the main transmission season. This is consistent with an observed recovery in the parasite rate, which had been reduced to a very low level by regular mass drug administration through the preceding dry season.The analysis was a tentative exercise in "epidemiological entomology" and it is suggested that in the postgraduate teaching of tropical hygiene, the epidemiological approach to entomology should be preferred to the classical morphological-bionomical approach.

Anopheles↗

[Control of Aedes aegypti in Martinique. Contribution of entomology studies].

The dengue prevention activities in Martinique are based on: Entomological surveillance (including the use of insecticide in all parts of the Island). Epidemiological (clinical, serological and virological) surveillance. Health Education (radio, TV, exhibitions, talks in primaries and secondaries schools, in associations,...). The main breeding sites of Aedes aegypti are maintained by human practices: flowers vases, containers, used tyres, waste... The role of those human practices in the standing of Aedes aegypti populations at high level in Martinique have lead us to emphasize entomological observations and Health education. The calculation of classical Breteau Index abstracts the nature and the productivity of the breeding sites (f.e.: no difference between a flower vase and a drum). In operational way, we have introduced a new approach for calculating the Breteau index value which includes the breeding sites nature and productivity. This approach permit us to adapt the Health education message in each geographical sector.

Aedes↗

Six forensic entomology cases: description and commentary.

Insects are known to be useful in estimating the postmortem interval (PMI). Here several cases are reported which show that a wide range of applications in medicolegal questions and hygiene together or apart from estimating the PMI can be answered by use of forensic entomology techniques, including close observation of larval development. Case 1 describes how blowfly larvae fell from a putrefied corpse, hid, and finally emerged from pupae three months after disinfection and renovation. In case 2, the entomological state of the decomposed corpse of a heroin user is described. Case 3 deals with a single adult Protophormia terranovae found in the skull of a partially mummified woman. Case 4 reports the finding of Serratia marcescens bacteria in red Muscina stabulans pupae which were found on a 5-day-old corpse. In case 5, blowfly eggs on the corpse of another heroin user are interpreted as an indication of the decedent being laid outside at night after his death in a flat. Case 6 deals with the finding of Parasarcophaga argyrostoma, which in Cologne might be an indicator species which tells if a corpse was lying outside at least for some time.

Adult↗

Trypanosoma cruzi transmission risk index (TcTRI): an entomological indicator of Chagas disease vectorial transmission to humans.

The goal of this project was to obtain an index of Chagas disease vectorial transmission to people living in infested houses. The proposed measure is an entomological indicator that estimates the number of risky bites that a human being receives per night. Based on very simple techniques, the method combines control measures--the use of fumigant canisters--with fast and accurate methods to look at the physiological and parasitological stage of insects. The index can be used to compare the importance of different vector species in Chagas transmission and also, as an entomological indicator of transmission risk in vector control programmes.

Animals↗

Recrudescence of visceral leishmaniasis in Albania: retrospective analysis of cases during 1997 to 2001 and results of an entomological survey carried out during 2001 in some districts.

The epidemiological status of zoonotic visceral leishmaniasis (VL) in Albania is almost unknown to international health organizations and to the scientific community. Results from a retrospective analysis of recent VL cases, and from an entomological survey carried out in summer 2001 are reported here. From January 1997 to December 2001, 867 parasitologically confirmed VL cases were recorded in 35 of 36 Albanian districts with an average of 173 cases/year and a cumulative morbidity of 2.8/10000 population. The temporal distribution of cases showed an increasing trend (from 144 to 209), indicating that cases have almost doubled during the past 10 years. A high proportion of the patients (67.6%) was children aged < 5 years. The entomological survey confirmed Phlebotomus neglectus as the probable vector, being the most abundant and widespread species. The increase in VL morbidity, 20-40-fold higher than in other southern European countries, could be attributed to increased susceptibility of infants to clinical disease or to variations in Leishmania infection associated with changes in canine reservoir and/or vector populations.

Adolescent↗

Four years' entomological study of the transmission of seasonal malaria in Senegal and the bionomics of Anopheles gambiae and A. arabiensis.

From 1993 to 1996, an entomological survey was conducted in the village of Ndiop, Senegal, as part of a research programme on malaria epidemiology and the mechanisms of protective immunity. Mosquitoes were captured on human bait and by indoor spraying. Species from the Anopheles gambiae complex were identified using the polymerase chain reaction, and Plasmodium falciparum infections were detected by enzyme-linked immunosorbent assay for circumsporozoite protein. The vector species identified were A. gambiae (33.9%), A. arabiensis (63.2%), A. melas (0.3%) and A. funestus (2.5%). Similar proportions of A. gambiae (74.2%) and A. arabiensis (73.8%) contained human blood; 27.0% of A. gambiae and 28.3% of A. arabiensis had fed on cattle. The sporozoite rates were similar for A. gambiae (3.2%) and A. arabiensis (3.7%). The annual entomological inoculation rates varied greatly depending on the year. There were 63, 17, 37 and 7 infected bites per person per year in 1993, 1994, 1995 and 1996 respectively. Transmission was highly seasonal, from July to October. A. arabiensis was responsible for 66% of malaria transmission, A. gambiae for 31%, and A. funestus for 3%.

Animals↗

Seasonal density, sporozoite rates and entomological inoculation rates of Anopheles gambiae and Anopheles funestus in a high-altitude sugarcane growing zone in Western Kenya.

An entomological study was conducted on vectors of malaria and their relative contribution to Plasmodium falciparum transmission in Mumias, a high-altitude site and large-scale sugarcane growing zone in Kakamega district, western Kenya. Anopheles gambiae s.l., the predominant vector species, represented 84% (n=2667) of the total Anopheles mosquitoes collected with An. funestus comprising only 16%. Polymerase chain reaction (PCR) identified all 600 specimens of the An. gambiae complex tested as An. gambiae sensu stricto, an indication that it is the only sibling species represented in the high-altitude sites in western Kenya. Plasmodium falciparum sporozoite rates of 6.3% (133/2118) for An. gambiae s.l. and 9.5% (38/402) for An. funestus by ELISA were obtained in Mumias. None of 1600 mosquitoes tested for P. malariae sporozoites was positive. ELISA tests of mosquito blood meals indicated a high tendency of anthropophagy, a behaviour contributing significantly to malaria transmission by the vector species, with 95.9%, 4.86% and 0.2% having taken at least one blood meal on human, bovine and avian hosts, respectively Malaria transmission intensity was low as revealed by the low entomological inoculation rates (EIR) recorded. The EIR values for An. gambiae s.l. were 29.2 infective bites per person per year (ib/p/year) and 17.5 ib/p/year for An. funestus in Mumias. The highest inoculation rate for both vector species was 7.0 ib/p/month in July. Plasmodium falciparum parasite rate among asymptomatic children was 55.4% and 44% in the wet (July-September) and dry (December-February) seasons, respectively. These results indicate that malaria transmission intensity in the high-altitude site is low but perennial, with transmission being maintained by An. gambiae s.s. and An. funestus.

Agriculture↗

An estimation of the entomological inoculation rate for Ifakara: a semi-urban area in a region of intense malaria transmission in Tanzania.

An entomological study on vectors of malaria and their relative contribution to Plasmodium falciparum transmission in the semi-urban area of Ifakara, south-eastern Tanzania, was conducted. A total of 32 houses were randomly sampled from the area and light trap catches (LTC) performed in one room in each house every 2 weeks for 1 year. A total of 147 448 mosquitoes were caught from 789 LTC; 26 134 Anopheles gambiae s.l., 615 A. funestus, 718 other anophelines and 119 981 culicines. More than 60% of the total A. gambiae s.l. were found in five (0.6%) LTCs, with a maximum of 5889 caught in a single trap. Of 505 A. gambiae s.l. speciated by polymerase chain reaction, 91.5% were found to be A. arabiensis. Plasmodium falciparum sporozoite enzyme-linked immunosorbent assay tests were performed on 10 108 anopheles mosquitoes and 39 (0.38%) were positive. Entomological inoculation rate (EIR) estimates were generated using a standard method and an alternative method that allows the calculation of confidence intervals based on a negative binomial distribution of sporozoite positive mosquitoes. Overall EIR estimates were similar; 31 vs. 29 [95% confidence interval (CI): 19, 44] infectious bites per annum, respectively. The EIR ranged from 4 (95% CI: 1, 17) in the cool season to 108 (95% CI: 69, 170) in the wet season and from 54 (95% CI: 30, 97) in the east of the town to 15 (95% CI: 8, 30) in the town centre. These estimates show large variations over short distances in time and space. They are all markedly lower than those reported from nearby rural areas and for other parts of Tanzania.

Animals↗

Entomological monitoring of annual mass drug administrations for the control or elimination of lymphatic filariasis.

Together, the interruption of transmission, through annual mass treatments with antifilarial drugs, and the alleviation of suffering in chronic cases form the principal strategy of the Global Programme to Eliminate Lymphatic Filariasis (GPELF). Entomological monitoring of the annual mass drug administrations is necessary to assess transmission levels and progress towards control or elimination of lymphatic filariasis. However, the traditional procedures for entomological monitoring, such as the dissection of mosquitoes caught manually, either as they come to bite at night or as they rest by day, are cumbersome, cost-prohibitive and often not feasible in large-scale control programmes. The collection of mosquitoes in traps and the assessment of their infection status using PCR-based assays offer promise and need to be established as a routine part of control programmes. It is proposed that-to verify the interruption of transmission or determine the prevalence of mosquito infection-1% of the villages/communities in each intervention unit be sampled, mosquitoes be collected from at least 100 households in each study village, and 10 female mosquitoes or all of those collected (whichever is the lower number) from each study house then be checked for infection.

Animals↗

Modelling entomological-climatic interactions of Plasmodium falciparum malaria transmission in two Colombian endemic-regions: contributions to a National Malaria Early Warning System.

BACKGROUND: Malaria has recently re-emerged as a public health burden in Colombia. Although the problem seems to be climate-driven, there remain significant gaps of knowledge in the understanding of the complexity of malaria transmission, which have motivated attempts to develop a comprehensive model. METHODS: The mathematical tool was applied to represent Plasmodium falciparum malaria transmission in two endemic-areas. Entomological exogenous variables were estimated through field campaigns and laboratory experiments. Availability of breeding places was included towards representing fluctuations in vector densities. Diverse scenarios, sensitivity analyses and instabilities cases were considered during experimentation-validation process. RESULTS: Correlation coefficients and mean square errors between observed and modelled incidences reached 0.897-0.668 (P > 0.95) and 0.0002-0.0005, respectively. Temperature became the most relevant climatic parameter driving the final incidence. Accordingly, malaria outbreaks are possible during the favourable epochs following the onset of El Niño warm events. Sporogonic and gonotrophic cycles showed to be the entomological key-variables controlling the transmission potential of mosquitoes' population. Simulation results also showed that seasonality of vector density becomes an important factor towards understanding disease transmission. CONCLUSION: The model constitutes a promising tool to deepen the understanding of the multiple interactions related to malaria transmission conducive to outbreaks. In the foreseeable future it could be implemented as a tool to diagnose possible dynamical patterns of malaria incidence under several scenarios, as well as a decision-making tool for the early detection and control of outbreaks. The model will be also able to be merged with forecasts of El Niño events to provide a National Malaria Early Warning System.

Animals↗

Evaluation of the impact of chemical control measures and entomological surveillance on Chagas' disease in the counties of Mambaí and Buritinópolis, Goiás State, Brazil.

Epidemiological surveillance activities were implemented in 1980 in Mambaí and Buritinópolis counties, Goiás State. Twenty years later the authors evaluated the impact of these vector control measures on Chagas' disease transmission, based on entomological indicators. Entomological investigation was conducted using the man-hour technique and covering all domiciles. In order to study vector food sources the stomach contents of triatomines were analyzed using the modified precipitins technique. Triatomines were shown to be present in 48 (71.6%) of the 67 locations. Peridomiciliary infestation rates in Mambaí and Buritinópolis were 8.7% and 12.1%, respectively, while intradomiciliary rates were 0.7% and 1.2%. Triatoma sordida was the species identified in 97.3% of all captured specimens. It was also the only species found to be naturally infected with Trypanosoma cruzi. Birds were the most frequent food source (45%) for Triatoma sordida. The most significant result was the complete absence of Triatoma infestans in the two counties.

Animals↗

The first documented forensic entomology case in Thailand.

The forensic entomology case described herein is the first such case documented in Thailand. A mummified corpse of a 32-yr-old man was discovered in a forested habitat, with the larvae of six species of flies (Diptera) found in association with the corpse at the time of its discovery, i.e., those of Hydrotaea (=Ophyra) spinigera Stein (family Muscidae), Piophila casei (L.) (family Piophilidae), Megaselia scalaris (Loew) (family Phoridae), Sagus sp. (family Stratiomyidae), and larvae of two unidenitified flesh fly species (family Sarcophagidae). The presence and age of the larval specimens of P. casei, M. scalaris, and H. spinigera gave entomological evidence that the postmortem interval for the corpse was 3-6 mo. This report also documets some of the forensically important fly species that occur in Thailand.

Adult↗

Yellow fever in the Gambia, 1978--1979: entomological aspects and epidemiological correlations.

An entomological survey was conducted in the Gambia in January 1979, during the last phase of a yellow fever (YF) outbreak which began during the previous rainy season. In the dry conditions which prevailed in January, Aedes aegypti was the only YF vector present. Two YF virus strains were isolated from females of this mosquito species caught in a village of western Gambia, where active human cases were documented. The ae. aegypti breeding sites were exclusively of the domestic type. Larval indices varied greatly from place to place, but generally appeared to correlate with the incidence of disease. A better understanding of the conditions that prevailed at the onset and during the early phase of the epidemic will require further entomological investigations. Nevertheless, it appears probable that initial transmission as by sylvatic vectors such as the Ae. furcifer-taylori group and possibly others such as Ae. luteocephalus, Ae. metallicus, and Ae. vittatus. As the outbreak progressed, interhuman transmission by Ae. aegypti also occurred, and this mixed epidemiological pattern later gave way to transmission by Ae. aegypti only when sylvatic vector populations declined in the dry season. We speculate that a prolongation of the rainy season during 1976--1978 was important in the origin of the outbreak. The relationship of this epidemic to the established focus of sylvatic YF in southeastern Senegal is discussed. The Gambian outbreak is considered the result of a recent northwesterly extension of the YF Emergence Zone.

Aedes↗

First recorded outbreak of yellow fever in Kenya, 1992-1993. II. Entomologic investigations.

The first recorded outbreak of yellow fever in Kenya occurred from mid-1992 through March 1993 in the south Kerio Valley, Rift Valley Province. We conducted entomologic studies in February-March 1993 to identify the likely vectors and determine the potential for transmission in the surrounding rural and urban areas. Mosquitoes were collected by landing capture and processed for virus isolation. Container surveys were conducted around human habitation. Transmission was mainly in woodland of varying density, at altitudes of 1,300-1,800 m. The abundance of Aedes africanus in this biotope, and two isolations of virus from pools of this species, suggest that it was the principal vector in the main period of the outbreak. A third isolate was made from a pool of Ae. keniensis, a little-known species that was collected in the same biotope. Other known yellow fever vectors that were collected in the arid parts of the valley may have been involved at an earlier stage of the epidemic. Vervet monkeys and baboons were present in the outbreak area. Peridomestic mosquito species were absent but abundant at urban sites outside the outbreak area. The entomologic and epidemiologic evidence indicate that this was a sylvatic outbreak in which human cases were directly linked to the epizootic and were independent of other human cases. The region of the Kerio Valley is probably subject to recurrent wandering epizootics of yellow fever, although previous episodes of scattered human infection have gone unrecorded. The risk that the disease could emerge as an urban problem in Kenya should not be ignored.

Adolescent↗

Short report: entomologic inoculation rates and Plasmodium falciparum malaria prevalence in Africa.

Epidemiologic patterns of malaria infection are governed by environmental parameters that regulate vector populations of Anopheles mosquitoes. The intensity of malaria parasite transmission is normally expressed as the entomologic inoculation rate (EIR), the product of the vector biting rate times the proportion of mosquitoes infected with sporozoite-stage malaria parasites. Malaria transmission intensity in Africa is highly variable with annual EIRs ranging from < 1 to > 1,000 infective bites per person per year. Malaria control programs often seek to reduce morbidity and mortality due to malaria by reducing or eliminating malaria parasite transmission by mosquitoes. This report evaluates data from 31 sites throughout Africa to establish fundamental relationships between annual EIRs and the prevalence of Plasmodium falciparum malaria infection. The majority of sites fitted a linear relationship (r2 = 0.71) between malaria prevalence and the logarithm of the annual EIR. Some sites with EIRs < 5 infective bites per year had levels of P. falciparum prevalence exceeding 40%. When transmission exceeded 15 infective bites per year, there were no sites with prevalence rates < 50%. Annual EIRs of 200 or greater were consistently associated with prevalence rates > 80%. The basic relationship between EIR and P. falciparum prevalence, which likely holds in east and west Africa, and across different ecologic zones, shows convincingly that substantial reductions in malaria prevalence are likely to be achieved only when EIRs are reduced to levels less than 1 infective bite per person per year. The analysis also highlights that the EIR is a more direct measure of transmission intensity than traditional measures of malaria prevalence or hospital-based measures of infection or disease incidence. As such, malaria field programs need to consider both entomologic and clinical assessments of the efficacy of transmission control measures.

Africa↗

Relationship between the entomologic inoculation rate and the force of infection for Plasmodium falciparum malaria.

We propose a stochastic model for the relationship between the entomologic inoculation rate (EIR) for Plasmodium falciparum malaria and the force of infection in endemic areas. The model incorporates effects of increased exposure to mosquito bites as a result of the growth in body surface area with the age of the host, naturally acquired pre-erythrocytic immunity, and the reduction in the proportion of entomologically assessed inoculations leading to infection, as the EIR increases. It is fitted to multiple datasets from field studies of the relationship between malaria infection and the EIR. We propose that this model can account for non-monotonic relationships between the age of the host and the parasite prevalence and incidence of disease. It provides a parsimonious explanation for the faster acquisition of natural immunity in adults than in children exposed to high EIRs. This forms one component of a new stochastic model for the entire transmission cycle of P. falciparum that we have derived to estimate the potential epidemiologic impact of malaria vaccines and other malaria control interventions.

Animals↗

Preventing dengue/dengue haemorrhagic fever outbreaks in the National Capital Territory of Delhi--the role of entomological surveillance.

Outbreaks of Dengue/Dengue Haemorrhagic Fever have been occurring in the National Capital Territory (NCT) Delhi from time to time. A massive outbreak of Dengue/DHF causing considerable mortality occurred in 1996 in the NCT, Delhi. Since this outbreak regular entomological surveillance has been instituted, for timely preventive action against Dengue/DHF. The Central Cross Checking Organisation (CCO) of the National Malaria Eradication Programme cross-checks Aedes surveillance activities in Delhi. In this paper we present our experiences in entomological surveillance in relation Dengue, to share them with other workers in this field.

Aedes↗