Sand Fly Activity Research Articles

Seasonal and nocturnal domiciliary human landing/biting behaviour of Lutzomyia (Lutzomyia) evansi and Lutzomyia (Psychodopygus) panamensis (Diptera; Psychodidae) in a periurban area of a city on the Caribbean coast of eastern Venezuela (Barcelona; Anzoátegui State)

In recent years, in addition to American cutaneous leishmaniasis (ACL), a significant number of cases of American visceral leishmaniasis (AVL) have been reported in periurban areas of Barcelona city (Anzoátegui State, Venezuela). We studied the bionomics of Lutzomyia (Lutzomyia) evansi and Lutzomyia (Psychodopygus) panamensis, possible vectors of AVL and ACL, respectively, in El Rincón, a periurban village of that city. To evaluate the seasonal domiciliary landing/biting activity of sandflies on human bait, a house was chosen in El Rincón. Landing catches were carried out between 18:00 and 06:00, once a month for a year. The results show the presence of 2 species, Lu. (Lu.) evansi (89·9%) and Lu. (Psy.) panamensis (10·1%). Lu. evansi was most abundant in the months of October and July, associated with the bimodal cycle of annual rainfall in the area. Maximum landing/biting activity of Lu. evansi was observed at 24:00 and 03:00. These findings suggest that at this time of the year and at these hours there is heightened risk of the transmission of AVL. Lu. panamensis monthly abundance also shows a direct association with rainfall and maximum landing/biting activity was observed between 02:00 and 03:00. The lower domiciliary abundance of Lu. panamensis suggests its greater importance in the extradomiciliary transmission of ACL.

A simulation model of the infection cycle of Leishmania mexicana in Neotoma micropus

A simulation model of transmission of Leishmania mexicana among Neotoma micropus by Lutzomyia anthophora was developed to predict the threshold vector density below which L. mexicana would be eliminated from a population of N. micropus within 2 years. Model results supported the hypothesis that N. micropus is a reservoir of L. mexicana. Leishmania mexicana could be maintained in a focus with an initial annual prevalence of 5.7%, which approximated the lowest non-zero prevalence found in field studies, and a peak annual vector density of only 11.4 female sand flies/woodrat. At a peak density of 2.8 female sand flies/woodrat, the prevalence declined below 1% (0.69%) at the end of 2 years. Simulations indicated that if the initial prevalence of infection was 27%, the highest annual prevalence found in the field studies, prevalence would remain > 1% (1.27%) after 2 years even if there was no sand fly activity.

L’évaluation écoépidémiologique du «risque leishmanien» au Sahara atlantique marocain. Intérêt heuristique de la relation «Phlébotomes-bioclimats»

The authors present the results of a survey carried out on leishmaniasis risk factors in the littoral zone of the Moroccan western Sahara. The paradigmatic concept of the greater importance of the vector than the reservoir suggests that the spatial, qualitative and quantitative distribution of sandflies are the risk markers for leishmaniasis. The analysis reported here was based on a series of sandfly samples made with sticky paper traps set in transects. Sampling was done with 2,604 traps at 36 stations during the period of maximum sand fly activity. The traps were distributed in two series, one strictly coastal and the other slightly diverging for some kilometers towards the interior. Over 1,043 km, 27 rural and 9 urban localities were sampled. Among the latter were Tan-Tan, Tarfaya, Layoun, Boujdour and Dakhla. Only 12 sandflies were caught among which a single specimen of the genus Phlebotomus. This scorcity of vector species coincides with the absence of leishmaniasis in the area studied. Twenty two dogs examined serologically by IFAT were negative and no parasites were demonstrable in 10 Psammomys obesus from around the airport at Tan-Tan. This is explained by the local climate along the Atlantic coast -a constant breeze from the NW/NE sector causing important modifications in the Saharan region : heavy clouds accompanied by an abundance of occult precipitation : and low summer temperatures. Of these factors, the violent and humid winds and the low summer temperatures are the most unfavourable for sandflies. As long as there are no changes in the climate, the risk of leishmaniasis can be expected to remain low in the coastal band. Moreover the buffering effect of the oceanic mass should ensure that this zone remains protected from the expected global warming which, in the coming decades, is likely to affect the periarid region of the continental Maghreb where P. papatasi, the common vector of Leishmania major, is widely distributed with the exception of the littoral zone.

Use of weather data and remote sensing to predict the geographic and seasonal distribution of Phlebotomus papatasi in southwest Asia.

Sandfly fever and leishmaniasis were major causes of infectious disease morbidity among military personnel deployed to the Middle East during World War II. Recently, leishmaniasis has been reported in the United Nations Multinational Forces and Observers in the Sinai. Despite these indications of endemicity, no cases of sandfly fever and only 31 cases of leishmaniasis have been identified among U.S. veterans of the Persian Gulf War. The distribution in the Persian Gulf of the vector, Phlebotomus papatasi, is thought to be highly dependent on environmental conditions, especially temperature and relative humidity. A computer model was developed using the occurrence of P. papatasi as the dependent variable and weather data as the independent variables. The results of this model indicated that the greatest sand fly activity and thus the highest risk of sandfly fever and leishmania infections occurred during the spring/summer months before U.S. troops were deployed to the Persian Gulf. Because the weather model produced probability of occurrence information for locations of the weather stations only, normalized difference vegetation index (NDVI) levels from remotely sensed Advanced Very High Resolution Radiometer satellites were determined for each weather station. From the results of the frequency of NDVI levels by probability of occurrence, the range of NDVI levels for presence of the vector was determined. The computer then identified all pixels within the NDVI range indicated and produced a computer-generated map of the probable distribution of P. papatasi. The resulting map expanded the analysis to areas where there were no weather stations and from which no information was reported in the literature, identifying these areas as having either a high or low probability of vector occurrence.

Nocturnal activity patterns of Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Nocturnal activity of the sand fly Lutzomyia longipalpis (Lutz & Neiva) was studied from August 1991 to July 1992 in a small rural community in Colombia where American visceral leishmaniasis is endemic. During 2 or 3 nights each month, sand flies were collected with hand-held aspirators each hour between 1730 and 0630 hours, from a pigpen and a cattle corral located 30 m apart. Host-seeking activity of L. longipalpis adults was characterized by 2 general patterns: (1) adult sand fly activity increased shortly after sunset and continued until just after sunrise, and (2) peak sand fly activity was greatest early in the evening (1830-2330 hours) and then declined steadily toward morning. Female L. longipalpis activity generally increased after 2030 hours, whereas that of males remained constant or declined as the evening progressed. There were seasonal differences in sand fly abundance between the 2 sites: peak abundance in the cattle corral occurred during hot, dry periods, whereas maximum abundance in the pigpen occurred when relative humidity was higher. Influence of relative humidity on activity varied with season. Sand fly activity tended to decrease at temperatures below 24 degrees C and increase in the presence of moonlight.

The distance of attraction of a human bait to Lutzomyia verrucarum (Diptera: Psychodidae) in crops

AbstractLutzomyia verrucarum (Townsend) is an abundant anthropophilic phlebotomine sandfly in the Peruvian Andes between 1500 m and 3000 m asl, where it has been incriminated as a vector of both Leishmania peruviana (cutaneous leishmaniasis) and Bartonella bacilliformis (bartonellosis). Previous studies of this vector demonstrated that sandfly activity, measured by sticky traps, was related to crop type. In this paper, we report the results of a field experiment in Peru (Department of Ancash) which show that a single human host in a crop does not attract Lu. verrucarum from distances of 5 m or more, and that there is a positive correlation between the number of Lu. verrucarum collected by sticky traps and the number attracted to a human host in the same field. The results imply that variation in sandfly activity between crop types could lead to differential risk of both leishmaniasis and bartonellosis for humans working at night in different crops.

Comparative activity of phlebotomine sandflies (Diptera: Psychodidae) in different crops in the Peruvian Andes

AbstractSignificant inter-crop variation in the abundance of phlebotomine sandflies, mostly Lutzomyia verrucarum Townsend, and five aphid species (Hemiptera: Aphididae), was demonstrated by repeated castor oil sticky trap collections in two valleys in the Peruvian Andes. Sandfly populations were significantly higher in fruit crops than in ground crops. Sticky trap collections also proved to be a suitable method for measuring aphid relative abundance in crops. As aphid honeydew is a natural sugar source for phlebotomine sandflies, the relationship between the activities of sandflies and aphids was investigated in inter-crop comparisons. Significant correlations were detected between sandfly abundance and two of the major aphid species, Aphis gossypii Glover and Eriosoma lanigerum (Hausmann), in one valley, but indirect explanations for these apparent associations cannot be ruled out.

Arabian sandflies (Diptera: Psychodidae) prefer the hottest nights?

A vehicle-mounted net was used to collect hourly samples of sandflies on 15 nights during June in northern Oman. Every half hour, the temperature, relative humidity, wind velocity and light intensity were measured (there was no cloud or rainfall during this period). The sandflies caught were mainly Phlebotomus alexandri and Sergentomyia clydei. Their circadian activity increased rapidly after sunset (18.50 hours). The high level of activity was fairly constant during 9h of darkness until dawn, when it decreased rapidly. A few flies were still active at 07.00 hours, 1.5h after sunrise. A multiple regression showed that the main factor affecting sandfly activity was light intensity. When this factor was removed, by considering only the 135 catches collected during the 9h of darkness, the second most important factor was low relative humidity, followed by low wind velocity. Temperature was not a significant factor in the analysis, because of its strong negative correlation with humidity. However, when the effect of humidity was removed from the regression, high temperature became significant, but less important than wind. The regressions showed that, for flight activity, the optimum humidity was around 10%; the probable maximum wind velocity was 3.5 m s-1 and 11 degrees C was the probable minimum temperature. Thus, when the 4 nights with highest catches (200-260 flies/night) were compared with the 4 nights with lowest catches (50-120 flies/night), the best nights had a low humidity (10-25%) and low wind speed (< 0.3 m s-1) in combination with highest temperatures (31-43 degrees C).

Epidemiology of Cutaneous Leishmaniasis at A Focus Monitored by The Multinational Force and Observers in the Northeastern Sinai Desert of Egypt

A longitudinal epidemiologic study of cutaneous leishmaniasis (CL) transmission was conducted between July 1989 and June 1991 in a 1,200-km2 sector of the northeastern Sinai Desert monitored by the Multinational Force and Observers (MFO), an international peace keeping mission between Egypt and Israel. The occurrence of human cases, sand fly density, rodent collection, and isolations of Leishmania confirmed only one of four surveyed locations as a significant focus of CL transmission. Phlebotomus papatasi, the only anthropophilic sand fly species encountered at this focus, comprised more than 96% of the sand fly population and attained human landing densities exceeding 100 sand flies/person/hr during 1990. Seasonal activity of this species ranged from April to November, with highest densities occurring during the period May-September. A peak promastigote infection rate of 2.4% (13 of 534) was observed in P. papatasi during July 1990. Twelve of the 60 (20%) persons at risk during the six months of intense sand fly activity at this site developed lesions consistent with CL; L. major was isolated from nine (75%) of these cases. Leishmania major infection was acquired by two of 22 (9%) sentinel hamsters used during the same period. More than 97% of the 897 wild rodents trapped at this site were desert gerbil species. Leishmania major was the only Leishmania isolated from human, sand fly, wild rodent (Gerbillus pyramidum), and sentinel hamster infections that originated at site Check point 1-Delta, the focus of CL transmission within jurisdiction of the MFO. The altered ecology of this area, created by construction of a dam, may contribute significantly to the transmission dynamics of CL at this focus.

Monthly variation in natural infection of the sandflyLutzomyia ayacuchensiswithLeishmania mexicanain an endemic focus in the Ecuadorian Andes

In order to collect information on the role of Lutzomyia ayacuchensis in the transmission of leishmaniasis in a newly discovered Andean endemic focus in Ecuador, a longitudinal field study was carried out over 13 months. Monthly dissections were made of a minimum of 200 anthropophilic sandflies, collected at night during the month. A total of 2600 flies was separated from a small number of Lu. osornoi, another anthropophilic species in the area, and dissected; 95 (3.65%) were naturally infected with Leishmania mexicana promastigotes. The parasites were always located in the sandfly midgut. The current study revealed a marked monthly variation both in natural infections with Leishmania and in biting activity of sandflies in the endemic area, demonstrating a high transmission rate during the period from the early rainy season to the early or mid dry season (February to July).

Salivary apyrase activity of some old world phlebotomine sand flies

Salivary gland homogenates of three Old World phlebotomine sand flies ( Phlebotomus papatasi, P. argentipes and P. perniciosus) contained abundant ATPase and ADPase activities, indicating the presence of an apyrase activity. These activities had an optimum pH around 8.0 and were activated by Ca 2+ but not Mg 2+. Both hydrolytic activities and salivary protein content were significantly reduced after the female sand fly took a blood meal indicating a secretory fate for the enzymic activities and salivary gland contents during the feeding process. In contrast to the above mentioned species, the salivary apyrase activity of P. colabaensis is much less abundant. Salivary gland homogenates of P. papatasi, P. argentipes and P. perniciosus inhibited ADP-induced platelet aggregation of citrated rabbit platelet rich plasma. It is suggested that salivary apyrase activity, as in some other blood-sucking arthropods, helps the blood-feeding process by preventing host platelet aggregation.

The man-biting activity of phlebotomine sand flies (Diptera: Psychodidae) in a tropical wet forest environment in Colombia

The purpose of this study was to investigate the temporal and spatial attributes of the man-biting activity of phlebotomine sand flies in a Tropical Wet Forest environment. The study was undertaken in a sparsely populated region of the east central portion of the Department of Antioquia, Colombia. With three two-man teams as bait, catches of approximately 10 hours duration during the day and approximately 13 hours for the night and twilight period were made at three separate forest locations and six diverse clearing sites. In the forest series of catches, the predominant man-biting species and their percentage of the catch were Lutzomyia hartmanni (56%), L. trapidoi (22%), and L. yuilli (13%). In the clearing series of catches the predominant species were L. hartmanni (56%), L. gomezi (16%), L. yuilli (9%), and Warileya rotundipennis (9%). For most species, both the magnitude and vertical stratification of their man-biting activity tended to be quite variable between the three forest sites. These differences were thought to be related to local variations in forest structure. Between-site differences in the magnitudes of biting activity were ieast pronounced in the understory. L. trapidoi, and to a lesser extent L. yuilli, were reluctant to bite at ground level in either the forest or clearing habitats. Their diminished biting activity at ground level appeared to primarily account for the greater similarity of the clearing catches to the forest floor catches than to those in the understory and canopy. In the clearing series of catches, the biting activity of L.hartmanni, L. trapidoi, and L. yuilli was detected to be significantly greater at the two forest edge sites than at those sites within the clearing. Diversity of man-biting activity in the clearing habitat was determined to be greatest at a site situated at the edge of pioneer vegetation and pasture. The pioneer vegetation extended to this location from the forest about 130 m away. The man-biting activity of phlebotomine sand flies in the Providencia study area was primarily nocturnal although crepuscular patterns were exhibited by L. bifoliata within the forest and by L. gomezi at the clearing sites. The temporal pattern of biting activity of each of the predominant forest species, i.e., L. hartmanni, L. trapidoi, and L. yuilli, was quite variable from one night to another and there was often a sharp peak in the biting activity. When such variations were averaged, the summarizing pattern tended to distort the true nature of the biting activity and only defined a rather broad interval of time in which biting activity was likely to be concentrated. There was no indication of a nightly pattern of vertical movement by any of these three species. The biting activity of most species appeared to be concentrated at a somewhat earlier time in the clearing habitat than in the forest. The magnitude of man-biting activity for all species combined was relatively uniform throghout the year; however, the dry season was unusually wet. Most of the individual species also did not appear to have pronounced seasonal fluctuations in biting acitivity although L. panamensis was a notable exception. The patterns of man-biting activity exhibited by L. gomezi suggest that it is the species most likely to transmit dermal leishmaniasis to man in the region where our study was conducted. The phlebotomine sand fly assemblage of the Providencia study area is compared with that described from other locations in Colombia and Panama. For each of the common man-biting species in the study area, a review of the literature pertaining to their biology is included.

Daily and seasonal man-biting activity of phlebotomine sandflies in Panama.

The daily and seasonal man-biting activity of 7 anthropophilic species of phlebotomine sandflies was recorded in a Panamanian forest over a period of one year. Lutzomyia olmeca, L. panamensis , and L. pessoana were predominantly active at ground level, L. gomezi, L. sanguinaria, L. trapidoi , and L. ylephiletrix in the forest canopy. The distribution of daily biting activity at ground level was 45.9% crepuscular, 39.0% nocturnal, and 15.1% diurnal. The relatively high level of diurnal biting was due to one species, L. pessoana . In the forest canopy the distribution was 35.7% crepuscular, 63.7% nocturnal, and only 0.6% diurnal. The seasonal manbiting activity was not totally in accord with either specific or total population trends, indicating that the biting rate at a particular time was related not only to sandfly density but to other undefined factors, including variation in physiological state of female flies.

Leishmaniasis in the Sudan Republic

Leishmaniasis in the Sudan Republic