Anthropophagy and aggregation behaviour of the sandfly Phlebotomus argentipes in Sri Lanka

ABSTRACT. The visceral leishmaniasis (VL) vector Phlebotomus argentipes Annandale & Brunetti is widely distributed throughout the Indian sub-continent and S.E. Asia. The absence of VL in areas such as Sri Lanka has been attributed to the zoophilic nature of P.argentipes , since they were not recorded biting man.
Field studies on P. argentipes were undertaken in the central highlands of Sri Lanka, near Kandy, in May 1988. Male sandflies outnumbered females on cows by 19:1, and were regularly spaced at all densities. This behaviour is considered analagous to swarming in other Nematocera. However, all-night human-biting catches show the biting rate to be similar (mean=8.4, range 2–25 bites per night over ten consecutive nights) to that in N.E. India where VL is endemic. This anthropophagy was maintained during laboratory colonization.     

Molecular and biochemical characterization of a sand fly population from Sri Lanka: evidence for insecticide resistance due to altered esterases and insensitive acetylcholinesterase

With an increasing incidence of cutaneous leishmaniasis in Sri Lanka, particularly in northern provinces, insecticide-mediated vector control is under consideration. Optimizing such a strategy requires the characterization of sand fly populations in target areas with regard to species composition and extant resistance, among other parameters. Sand flies were collected by human bait and cattle-baited net traps on Delft Island, used as an illegal transit location by many refugees returning to the north of Sri Lanka from southern India where leishmaniasis is endemic. For species identification, genomic DNA was extracted and a fragment of the ribosomal 18S gene amplified. The sequence from all flies analysed matched that of Phlebotomus argentipes Annandale & Brunetti, the primary vector in India and the most likely vector in Sri Lanka. Independent morphological analysis also identified P. argentipes. To establish the current susceptibility status of vector species, data were obtained at the biochemical level, from which potential cross-resistance to alternative insecticides can be predicted. The Delft Island collection was assayed for the activities of four enzyme systems involved in insecticide resistance (acetylcholinesterase, non-specific carboxylesterases, glutathione-S-transferases and cytochrome p450 monooxygenases), establishing baselines against which subsequent collections can be evaluated. There was preliminary evidence for elevated esterases and altered acetylcholinesterase in this population, the first report of these resistance mechanisms in sand flies to our knowledge, which probably arose from the malathion-based spraying regimes of the Anti-Malarial Campaign.     

The efficacy of indoor CDC light traps for collecting the sandfly Phlebotomus argentipes, vector of Leishmania donovani

The efficacy of light traps for collecting sandflies (Diptera: Psychodidae) varies both inter-specifically and intra-specifically (by gender and physiological status) as a result of significant differences in phototropic and other behavioural characteristics. The efficacy of miniature CDC light traps for collecting Phlebotomus argentipes Annandale & Brunetti, a vector of Leishmania donovani Laveran & Mesnil (Kinetoplastida: Trypanosomatidae), was assessed in the Indian state of Bihar. Sandflies were collected during the night from 16 houses in each of three villages over 3 months (four times at fortnightly intervals) using CDC light traps indoors, and by aspirator collection (carried out by one person for 30 min/house) from the walls of the same houses the following morning. Incidence rate ratios (IRRs) between CDC light trap collections and aspirator collections were obtained through a negative binomial regression with household as random effect. CDC light traps were especially effective in catching males (IRR 3.08, 95% confidence interval [CI] 2.12-4.46) and unfed females (IRR 3.50, 95% CI 2.37-5.16) of P. argentipes, and to a lesser extent gravids (IRR 1.77, 95% CI 1.07-2.93). However, only a relatively small proportion of all blood-fed P. argentipes were collected by light trap (IRR 0.45, 95% CI 0.28-0.73). Despite its limitations in collecting blood-fed female sandflies, the CDC light trap appears to trap a sufficient proportion of the indoor population of sandflies for sampling purposes, and as this light trap is also more convenient and more easily standardized than the aspirator method, we conclude that it is the most efficient method for monitoring P. argentipes populations in the Indian subcontinent.     

The role of Palmyra palm trees (Borassus flabellifer) and sand fly distribution in northeastern India

Visceral leishmaniasis (VL), known as Kala-azar in India, is a parasite transmitted by the bite of the sand fly vector Phlebotomus argentipes. Published information on the species indicates it is a poor flyer, mainly hopping and gliding. This study describes the vector as more arboreal than previously documented. Data collected indicate the ability of P. argentipes and Sergentomyia spp to attain vertical heights in Palmyra palm trees Borassus flabellifer up to 18.4 m above ground level. To determine if sand flies were either climbing the tree trunk to rest in the canopy or flying, sticky traps were set around the tree trunk and checked for captures overnight. CDC traps set in the palm tree canopy resulted in the capture of 5,067 sand flies, 3,990 of which were P. argentipes. Traps were set during daylight hours to determine if sand flies remained and rested in the canopy. A total of 128 sand flies were trapped over 29 trap days in the palm trees. With the CDC traps, 130 P. argentipes and no Sergentomyia spp were captured. The converse was true for the sticky traps set around tree trunks 3 m below the CDC traps. Of the 105 sand flies collected, only one was P. argentipes and 104 were Sergentomyia spp. As reported elsewhere, this indicates Sergentomyia spp tend to climb and hop, wheareas P. argentipes are capable of longer and more sustained flight. Data presented herein suggest that P. argentipes is more exophylic and exophagic than previously reported. These findings have implications for sand fly control.     

Use of a Mixture Statistical Model in Studying Malaria Vectors Density

Vector control is a major step in the process of malaria control and elimination. This requires vector counts and appropriate statistical analyses of these counts. However, vector counts are often overdispersed. A non-parametric mixture of Poisson model (NPMP) is proposed to allow for overdispersion and better describe vector distribution. Mosquito collections using the Human Landing Catches as well as collection of environmental and climatic data were carried out from January to December 2009 in 28 villages in Southern Benin. A NPMP regression model with “village” as random effect is used to test statistical correlations between malaria vectors density and environmental and climatic factors. Furthermore, the villages were ranked using the latent classes derived from the NPMP model. Based on this classification of the villages, the impacts of four vector control strategies implemented in the villages were compared. Vector counts were highly variable and overdispersed with important proportion of zeros (75%). The NPMP model had a good aptitude to predict the observed values and showed that: i) proximity to freshwater body, market gardening, and high levels of rain were associated with high vector density; ii) water conveyance, cattle breeding, vegetation index were associated with low vector density. The 28 villages could then be ranked according to the mean vector number as estimated by the random part of the model after adjustment on all covariates. The NPMP model made it possible to describe the distribution of the vector across the study area. The villages were ranked according to the mean vector density after taking into account the most important covariates. This study demonstrates the necessity and possibility of adapting methods of vector counting and sampling to each setting.     

Modeling the influence of local environmental factors on malaria transmission in Benin and its implications for cohort study

Malaria remains endemic in tropical areas, especially in Africa. For the evaluation of new tools and to further our understanding of host-parasite interactions, knowing the environmental risk of transmission--even at a very local scale--is essential. The aim of this study was to assess how malaria transmission is influenced and can be predicted by local climatic and environmental factors.As the entomological part of a cohort study of 650 newborn babies in nine villages in the Tori Bossito district of Southern Benin between June 2007 and February 2010, human landing catches were performed to assess the density of malaria vectors and transmission intensity. Climatic factors as well as household characteristics were recorded throughout the study. Statistical correlations between Anopheles density and environmental and climatic factors were tested using a three-level Poisson mixed regression model. The results showed both temporal variations in vector density (related to season and rainfall), and spatial variations at the level of both village and house. These spatial variations could be largely explained by factors associated with the house's immediate surroundings, namely soil type, vegetation index and the proximity of a watercourse. Based on these results, a predictive regression model was developed using a leave-one-out method, to predict the spatiotemporal variability of malaria transmission in the nine villages.This study points up the importance of local environmental factors in malaria transmission and describes a model to predict the transmission risk of individual children, based on environmental and behavioral characteristics.     

Notes about the impact of human seasonal migration on malaria spreading in rural Venezuela

This paper considers the effect of social and cultural factors on malaria spreading in rural Venezuela. It argues that standard vertical malaria control programs are inclined to ignore local workplace and living conditions instead of recruiting traditional practices into the planning scenario for more effective malaria control. An epidemiological survey on people migrating from malaria endemic areas to non-endemic region studied by blood films and a Plasmodium falciparum in vivo test. The results of the survey on people migrating from malaria endemic areas to non endemic regions revealed that 138 (118 males and 20 females) (23.3%) had fever (38.2-39 degrees C), malarial parasites were detected in the blood films of 49 (35.5%) from 138 febrile (parasitaemic) patients, and 45 (91.8%) of the parasitaemic cases were infected with P. falciparum; other four cases carried P. vivax only. Differences in prevalence, parasites load and the density of infection were observed between the three age groups. The asexual parasite load and the density of parasites (asexual and sexual forms) were appreciably higher in older children than in the other two age-groups (P < 0.001 for each). In the Plasmodium falciparum in vivo test, nine (22.5%) patients presented resistance grade III. People with transient jobs in malaria endemic areas could transport the parasites to non-endemic areas establishing a new malaria focus during seasonal migration activities.     

Distribution of Mycobacterium ulcerans in buruli ulcer endemic and non-endemic aquatic sites in Ghana

Mycobacterium ulcerans, the causative agent of Buruli ulcer, is an emerging environmental bacterium in Australia and West Africa. The primary risk factor associated with Buruli ulcer is proximity to slow moving water. Environmental constraints for disease are shown by the absence of infection in arid regions of infected countries. A particularly mysterious aspect of Buruli ulcer is the fact that endemic and non-endemic villages may be only a few kilometers apart within the same watershed. Recent studies suggest that aquatic invertebrate species may serve as reservoirs for M. ulcerans, although transmission pathways remain unknown. Systematic studies of the distribution of M. ulcerans in the environment using standard ecological methods have not been reported. Here we present results from the first study based on random sampling of endemic and non-endemic sites. In this study PCR-based methods, along with biofilm collections, have been used to map the presence of M. ulcerans within 26 aquatic sites in Ghana. Results suggest that M. ulcerans is present in both endemic and non-endemic sites and that variable number tandem repeat (VNTR) profiling can be used to follow chains of transmission from the environment to humans. Our results suggesting that the distribution of M. ulcerans is far broader than the distribution of human disease is characteristic of environmental pathogens. These findings imply that focal demography, along with patterns of human water contact, may play a major role in transmission of Buruli ulcer.     

Mineral content of water and food in fluorotic villages and prevalence of dental fluorosis

The fluoride (F), calcium (Ca), magnesium (Mg), zinc (Zn), copper (Cu), and phosphorus (P) content in potable water and food samples (cereals, pulses, and vegetables) from endemic and nonendemic villages for fluorosis were analyzed. It was found that the F content in water was significantly higher (p<0.01) in endemic villages (4.20±1.6 ppm) than control villages (0.63±0.15 ppm), whereas the Ca, Cu, and Mg contents were found to be significantly lower (p<0.05) in endemic villages compared to control villages. However, there was no significant difference in Zn and P contents between the villages. Foods (cereals, pulses, and vegetables) grown in endemic villages contained significantly higher (p<0.01) fluoride content as compared to control villages. There was no significant difference in Ca, Mg, P, and Zn contents in food grown in endemic and control villages. Copper content in cereals (p<0.05), pulses (p<0.01), and vegetables (p<0.01) in endemic villages was found significantly higher as compared to control villages. The overall prevalence of dental fluorosis in six endemic villages was 97.4% in boys and 96% in girls, which was significantly higher (p<0.01) than that of control villages, where it was 10.5% in boys and 8.3% in girls. The prevalence of dental fluorosis was positively correlated (r=0.125, p<0.01) to fluoride and negatively correlated to Ca and Cu content in drinking water in endemic villages.     

Suboptimal Selenium Supply—A Continuing Problem in Keshan Disease Areas in Heilongjiang Province

This study explores whether the declining prevalence of Keshan disease is associated with increasing selenium levels in Keshan disease areas in Heilongjiang province. Six counties endemic with Keshan disease and three non-endemic counties were selected as study areas. In each county, two townships and in each township one village were chosen in which to survey ten families about head hair, grain, and soil samples and to obtain demographic information. Selenium was measured with hydride generation-atomic fluorescence spectrometry. In each county endemic with Keshan disease, one of the villages was chosen to investigate the prevalence of the disease. We collected 534 head hair samples, 446 staple food samples, and 180 soil samples. The selenium levels of head hair and corn in the endemic counties were significantly lower than those in non-endemic counties. Family demographic information was homologous except for the composition of staple food. More residents in Keshan disease areas preferred flour and corn. The detection rate for latent Keshan disease had a significantly negative correlation with the corn selenium level in six counties endemic with Keshan disease. As the population in this region is still at risk for Keshan disease, selenium surveillance measures should be intensified.     

Appraisal of Phlebotomus argentipes habitat suitability using a remotely sensed index in the kala-azar endemic focus of Bihar,India

Visceral leishmaniasis, or kala-azar, is recognised as a serious emerging public health problem in India. In this study, environmental parameters, such as land surface temperature (LST) and renormalised difference vegetation indices (RDVI), were used to delineate the association between environmental variables and Phlebotomus argentipes abundance in a representative endemic region of Bihar, India. The adult P. argentipes were collected between September 2009-February 2010 using the hand-held aspirator technique. The distribution of P. argentipes was analysed with the LST and RDVI of the peak and lean seasons. The association between environmental covariates and P. argentipes density was analysed a multivariate linear regression model. The sandfly density at its maximum in September, whereas the minimum density was recorded in January. The regression model indicated that the season, minimum LST, mean LST and mean RDVI were the best environmental covariates for the P. argentipes distribution. The final model indicated that nearly 74% of the variance of sandfly density could be explained by these environmental covariates. This approach might be useful for mapping and predicting the distribution of P. argentipes, which may help the health agencies that are involved in the kala-azar control programme focus on high-risk areas.     

A longitudinal entomologic survey on the transmission of malaria in Ouagadougou (Burkina Faso)

A longitudinal entomological malaria survey was carried out in five zones of the town of Ouagadougou, Burkina Faso, and in three neighbouring villages. The main vector is Anopheles gambiae s.l. with An. funestus having a role in some localities during the dry season. Pyrethrum spray catches were carried out once or twice per month to determine variations in vector density. Inoculation rates were estimated from the number of blood-fed vectors per man and from the sporozoite rates. Larval sampling was routinely carried out all over the urban area in order to map the larval breeding sites. Widely different degrees of malaria transmission were documented in the urban area mainly related to the spatial and temporal distribution of An. gambiae larval breeding sites. Higher inoculation rates, depending both on higher vector densities and sporozoite rates, were documented in the villages.     

Temporal distribution and spatial pattern of abundance of the Rift Valley fever and West Nile fever vectors in Barkedji, Senegal

The temporal distribution and spatial pattern of abundance of mosquito vectors of Rift Valley fever (RVf) and West Nile fever (WNf) were studied during the 2005 and 2006 rainy seasons at Barkedji, Senegal. Mosquitoes were collected every two weeks with CDC light traps with dry ice at 79 sites including temporary ponds, barren, shrubby savannah, wooded savannah, steppes, and villages at different distances (between 0 and 600 m) from the nearest pond. The temporal distributions of these vectors varied between 2005 and 2006 and were positively correlated with rainfall for Aedes (Aedimorphus) vexans Patton, with rainfall after a lag time of one month for Culex (Culex) poicilipes (Theobald) and Culex (Culex) neavei Theobald. All the vectors had their highest abundances and parity rates between September and November. The highest vector abundances were observed in the barren and temporary ponds. The distance of trap location to the nearest ponds was negatively correlated to the abundance of the vectors. Taking into account the linear regression equations, it was predicted that mosquitoes would not disperse and be collected by the light trap, up to 1,500 m to the nearest ponds. The implications of these findings in the epidemiology and control of RVF and WNF at Barkedji are discussed.     

Modelling the biological aspects of local endemism in South African Fynbos

The biological attributes, dispersal mode, growth form, and regeneration strategy were determined for the endemic and non-endemic flora of the southern Langeberg, Cape Province, South Africa.—Logistic regression analysis was used to assess the simultaneous effects and interactions between these biological attributes on the occurrence of endemism. The model allowed numerical estimation of the probability that a species with a given set of attributes would be endemic.—This approach extends a contingency table analysis of the data, which merely indicated the association between individual biological traits and endemism. Furthermore, the logistic model allows scope for the analysis of the influence of biological traits in determining endemism in other floras, and also tentative prediction of the probability of endemism in species with combinations of biological traits not yet observed in the flora of the southern Langeberg.     

First Assessment for the Presence of Phlebotomine Vectors in Bavaria,Southern Germany,by Combined Distribution Modeling and Field Surveys

Leishmaniasis is caused by protozoa of the genus Leishmania and transmitted by sand flies from mammalian reservoirs to humans. In recent years, a northward spread of L. infantum from highly endemic Mediterranean countries into previously non-endemic Central European areas has been suspected based on presumed sporadic cases of autochthonous leishmaniasis. Here, we investigated whether sand flies are prevalent in Bavaria in Southern Germany, a federal state in which autochthonous cases have previously been reported. Considering the present and future climatic conditions, we determined whether Bavaria is suitable for five sand fly species with assumed spreading tendencies towards Central Europe: Phlebotomus ariasi, P. neglectus, P. perfiliewi and P. perniciosus that are known vectors for Leishmania in Europe, and P. mascittii, a suspected but not proven vector. Within Bavaria we defined sampling regions based on their climatic suitability and their spatial distance to the sites of the autochthonous cases and/or to areas of reported sand fly detection in states adjacent to Bavaria. At 155 locations in 7 sampling regions, CDC light traps were placed during 38 nights in the summers of 2009 and 2010, resulting in 202 trap-nights. All traps were negative for sand flies. The results suggest that Bavaria is not yet endemic for sand flies, but do not exclude the possibility of sporadic cases of autochthonous human or zoonotic Leishmania infections. This study, which combined methodological approaches from different disciplines, serves as reference for future surveys and risk analyses of sand flies and leishmaniasis in so far non-endemic areas of Europe.     

A morphologically distinct Phlebotomus argentipes population from active cutaneous leishmaniasis foci in central Sri Lanka

Although the reported aetiological agent of cutaneous leishmaniasis (CL) in Sri Lanka is Leishmania donovani, the sandfly vector remains unknown. Ninety-five sandflies, 60 females and 35 males, collected in six localities in the district of Matale, central Sri Lanka, close to current active transmission foci of CL were examined for taxonomically relevant characteristics. Eleven diagnostic morphological characters for female sandflies were compared with measurements described for Indian and Sri Lankan sandflies, including the now recognised Phlebotomus argentipes sensu lato species complex. The mean morphometric measurements of collected female sandflies differed significantly from published values for P. argentipes morphospecies B, now re-identified as Phlebotomus annandalei from Delft Island and northern Sri Lanka, from recently re-identified P. argentipes s.s. sibling species and from Phlebotomus glaucus. Furthermore, analysis of underlying variation in the morphometric data through principal component analysis also illustrated differences between the population described herein and previously recognised members of the P. argentipes species complex. Collectively, these results suggest that a morphologically distinct population, perhaps most closely related to P. glaucus of the P. argentipess. I. species complex, exists in areas of active CL transmission. Thus, research is required to determine the ability of this population of flies to transmit cutaneous leishmaniasis.     

A spatial study on serum selenoprotein P and Keshan disease in Heilongjiang Province,China

BackgroundFew spatial studies on serum selenoprotein P (SELENOP) and Keshan disease (KD) have been reported at the county-level in Heilongjiang province, China. This study aimed to provide visualized spatial epidemiological evidence of selenium molecular marker in residents living in endemic areas for the precise assessment of prevention, control, and elimination of KD.MethodsUsing a spatial ecological study design, 587 subjects living in cities, townships, and rural areas of 50 KD endemic counties and 37 non-endemic counties in Heilongjiang province were investigated. The serum SELENOP levels of the participants were measured by enzyme-linked immunosorbent assay. Thematic maps were created, and spatial regression analysis was conducted using ordinary least squares.ResultsThe mean serum SELENOP level of the 587 subjects was 7.4 ± 3.0 μg/mL. The mean levels of serum SELENOP were higher in cities (7.4 ± 2.9 μg/mL) and townships (7.9 ± 3.2 μg/mL) than in rural areas (6.0 ± 3.0 μg/mL). The mean levels of serum SELENOP were trending towards high levels in non-endemic areas (7.4 ± 3.0 μg/mL) than in KD endemic areas (6.3 ± 3.3 μg/mL). Spatial regression analysis showed that the serum SELENOP level was positively correlated with the per capita gross domestic product.ConclusionSelenium deficiency may still exist in some KD endemic counties in Heilongjiang province, including Lingdong, Nenjiang, and Baiquan; these counties should be considered as key areas for precision prevention, control, and elimination of KD. Inclusion of selenium in the national surveillance of KD will provide more evidence for the assessment of KD elimination from a selenium nutrition perspective.     

Management of insecticides for use in disease vector control: Lessons from six countries in Asia and the Middle East

Interventions to control the vectors of human diseases, notably malaria, leishmaniasis and dengue, have relied mainly on the action of chemical insecticides. However, concerns have been raised regarding the management of insecticides in vector-borne disease-endemic countries. Our study aimed to analyze how vector control insecticides are managed in selected countries to extract lessons learned.A qualitative analysis of the situation of vector control insecticides management was conducted in six countries. Multi-stakeholder meetings and key informer interviews were conducted on aspects covering the pesticide lifecycle. Findings were compared and synthesized to extract lessons learned. Centrally executed guidelines and standards on the management of insecticides offered direction and control in most malaria programs, but were largely lacking from decentralized dengue programs, where practices of procurement, application, safety, storage, and disposal were variable between districts. Decentralized programs were better at facilitating participation of stakeholders and local communities and securing financing from local budgets. However, little coordination existed between malaria, visceral leishmaniasis and dengue programs within countries. Entomological capacity was concentrated in malaria programs at central level, while dengue and visceral leishmaniasis programs were missing out on expertise. Monitoring systems for insecticide resistance in malaria vectors were rarely used for dengue or visceral leishmaniasis vectors. Strategies for insecticide resistance management, where present, did not extend across programs or sectors in most countries. Dengue programs in most countries continued to rely on space spraying which, considering the realities on the ground, call for revision of international guidelines.Vector control programs in the selected countries were confronted with critical shortcomings in the procurement, application, safety measures, storage, and disposal of vector control insecticides, with implications for the efficiency, effectiveness, and safety of vector control. Further international support is needed to assist countries in situation analysis, action planning and development of national guidelines on vector control insecticide management.     

Insecticide resistance status of three vectors of Japanese encephalitis in east central India

Japanese encephalitis (JE) has been reported in different districts of Odisha state (east central India) since 1992. During 2016, a major outbreak of JE and acute encephalitis syndrome (AES) occurred in the Malkangiri district of Odisha, causing 103 deaths in children, of which 37 were caused by JE and 66 by AES. Information on insecticide resistance in JE vectors is important for the selection of appropriate insecticides for use in vector control. The present study was designed to determine the resistance status of three important vectors of JE, Culex vishnui, Culex tritaeniorhynchus and Culex bitaeniorhynchus (Diptera: Culicidae), against dichlorodiphenyltrichloroethane (DDT), malathion and deltamethrin in three districts of Odisha state affected by JE. Female adult mosquitoes were collected using mouth aspirators both indoors and outdoors in JE‐affected villages and used in susceptibility bioassays following World Health Organization guidelines. Knock‐downs were recorded every 10 min up to 1 h and mortality rates were recorded at 24 h post‐exposure. Culex vishnui and Cx. tritaeniorhynchus showed resistance to DDT, malathion and deltamethrin, whereas Cx. bitaeniorhynchus was susceptible in all study districts. The information generated by this study will be highly useful in the planning and implementing of appropriate vector control operations for the prevention and control of JE in east central India.