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PubMed1985

Biting activity of two anthropophilic species of sandflies, Lutzomyia, in an endemic area of leishmaniasis in Ecuador.

The biting patterns of Lutzomyia trapidoi and Lu. hartmanni, vectors of leishmaniasis, were studied using a human bait in an endemic area on the Pacific slope of the Andes in Ecuador. The results suggest that Lu. trapidoi is primarily an early biter at dusk, with the first peak at 20.00-21.00 hours and the second at 03.00-04.00 hours; and that Lu. hartmanni bites more constantly throughout the night, with a pronounced peak between 23.00 and 24.00 hours. The biting activity, however, shows a marked variation at each site and between different collections at the same site. The activity and the biting places on man are discussed in relation to human infection with leishmaniasis in the area and the location of lesions on patients.

Animals↗
PubMed1987

Depth of penetration of vertebrate skin by phlebotomine sandflies (Diptera: Psychodidae).

The limited knowledge of penetration depth and its relation to Leishmania transmission is reviewed. Labrum length and maxillary dentition of a number of species of phlebotomines are compared. It appears that the labrum of Phlebotomus argentipes, the vector of kala-azar in eastern India, is only just long enough for obtaining a blood meal in normal human skin. More information on penetration depth is needed, and it might possibly be estimated from the length of the labium when it remains outside the skin and contracts. It would be necessary, however, to note the position of the labium which changes in relation to the labrum.

Animals↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon I. Prevailing Simulium vectors, their biting rates and age-composition at different distances from their breeding sites.

Along the main water courses in the sparsely populated areas of the Sous-Préfecture of Tcholliré, the vectors of onchocerciasis were mainly Simulium damnosum s. str. and S. sirbanum, together with a small proportion of S. squamosum. Over a period of one to three years, vector biting rates were measured at 23 fly-catching sites in the vicinities of nine villages with different endemicities of onchocerciasis. Annual Biting Rates (ABR) on man were estimated as 26,100-83,800 fly-bites per man per year along the rivers Mayo Rey and Vina du Nord, and 11,000-37,400 at rainy season tributaries. Biting rates decreased rapidly at increasing distances from the river, and were between 10,700 and 2400 at 2-10 km cross-country from the breeding site. Lowest biting rates (50-6000) were measured at the village centres. The ABR varied from year to year in relation to the water-discharge of the main rivers, the coefficient of variation of the mean being 34-49%. The parous rates were 64-73% at the perennial breeding sites and only 17-44% away from the breeding sites, indicating dispersal mainly of young nulliparous flies and a reduced flight-range after oviposition.

Age Factors↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon II. Seasonal and diurnal changes in the biting densities and in the age-composition of the vector population.

Near the perennial breeding sites in the main water courses the highest monthly biting rates were recorded from June to August (early rainy season) and again from December to February (dry season), but near the rainy season breeding sites in the affluents, or at fly-catching sites, more than 2 km inland from the nearest main river breeding site, the highest rates were recorded between August and December (mid-rainy to early dry season). The variation of the biting rates over the year depended on the waterflow of the main rivers and on the differential dispersal of the flies from the breeding sites during the dry and rainy seasons. At the beginning of the rainy season, when the rivers started flowing, an immigration of non-local flies was observed at the river Mayo Rey near Tcholliré, presumably coming from Simulium breeding sites in the Adamaoua mountains to the South. During three years 77,374 flies were caught by daily catches between 06.00 and 18.30 hours. During the dry season the biting activity of nulliparous and parous flies was highest between 09.00 and 10.00 hours and 16.00 and 17.00 hours, 9% and 22% of the total day-catches respectively. In the rainy season the peak biting rates occurred between 06.00 and 07.00 hours (9%) and again from 16.00 to 17.00 hours (14%). The lowest biting rates were observed between 11.00 and 12.00 hours in both dry and rainy seasons (4% and 3% of the total catch). Nulliparous flies showed higher variations in biting activity than did parous flies, leading to the highest proporation of parous flies during midday.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon IV. The different exposure to Simulium bites and transmission of boys and girls and men and women, and the resulting manifestations of onchocerciasis.

The sojourn times of the human population were monitored over one year at 12 sites in the vicinity of three villages in the Cameroon Sudan-savanna, where the Onchocerca volvulus transmission potentials had been measured one year previously. Boys stayed longer outside the villages, and were exposed 2.1 to 2.7 times more than girls to transmission of onchocerciasis, whereas the exposure of men was similar or only moderately higher than the exposure of women. In boys, the onset of infections and ocular lesions was earlier and the average microfilarial density at the buttock (2.2, 9.4 and 79.3 mff snip-1) was much higher than in girls (0.1, 5.8 and 42.2 mff snip-1 at the three villages respectively). These differences were maintained in the adult population, where the average microfilarial density was 52.3, 80.4 and 183.1 mff snip-1 in men and 15.6, 49.6 and 114.7 mff snip-1 in women. Ocular lesions due to onchocerciasis were found in 5, 13 and 55% of the male population in the three villages, as compared with 2, 3 and 8% of the female population. There was a close relationship between the degree of exposure to the transmission of disease and the resulting microfilarial load in the skin which was not different for the two sexes, and a similar trend was seen for the occurrence of ocular lesions due to onchocerciasis. The influence of an early and heavy infection on the evolution of disease manifestations is discussed.

Age Factors↗
PubMed1987

Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon V. What is a tolerable level of Annual Transmission Potential?

The prevalence and intensity of infection with Onchocerca volvulus were assessed in population surveys in nine villages, situated at different distances from Simulium damnosum s.l. breeding sites. The prevalence varied from 48 to 89%, the arithmetic mean densities of microfilariae per skin snip were between 16 and 109, and severe ocular lesions were found in from 1 to 22% of patients. Annual Transmission Potentials (ATP) were measured for up to three years in the near vicinity of nine villages at several fly-catching sites. Weighted means of the ATP over the three years, and of the sojourn times of the human population, were calculated at three of the villages, where the prevalence of onchocerciasis was 51, 61 and 89%. An average ATP of 100 larvae or less in the head, thorax and abdomen of the flies was associated with an onchocerciasis prevalence of 50 to 60%, a mean microfilarial density below 40 microfilariae per skin-snip, less than 5% of ocular lesions, and no onchocercal blindness. This value might therefore be considered to be an indication of the level to which the transmission must be reduced in the savanna in order to prevent the occurrence of severe ocular lesions or blindness. It is lower than the present level accepted by the Onchocerciasis Control Programme in the Volta River Basin.

Animals↗
PubMed1988

Transmission dynamics and estimates of malaria vectorial capacity for Anopheles balabacensis and An. flavirostris (Diptera: Culicidae) on Banggi island, Sabah, Malaysia.

Holoendemic malaria transmission in two small isolated forest communities and a coastal village was studied by (1) all night human bait collections of Anopheles species from inside and outside houses and (2) buffalo-biting and CDC light-trapping catches during March and November 1984. During the same period thick and thin blood films were collected from the human population, and spleen rates were determined in children from two to nine years of age. Using both the immunoradiometric assay (IRMA) and the dissection technique, more sporozoite-positive infections were detected in An. balabacensis and An. flavirostris in November than in March. IRMA confirmed the presence of Plasmodium falciparum sporozoites. An average of 76.2% of the An. balabacensis population lived long enough to have reached a point where infectivity with P. falciparum was possible in November. Although fewer than five adult females bit humans per night at any time, a resident could theoretically have received more than 160 infective bites in one year. A high frequency of feeding on humans, coupled with increased anopheline life expectancy, contributed to high estimates of falciparum malaria vectorial capacity (number of infections distributed per case per day); for An. balabacensis (1.44-7.44 in March and 9.97-19.7 in November) and for An. flavirostris (0.19-5.14 in March and 6.27-15.8 in November). These high values may explain the increased malaria parasite rates obtained from at least two forest communities. Correlation between actual and calculated rates of gametocytaemia was poorest in Kapitangan due to inadequate sampling of the human population. In Banggi island, malaria is stable and holoendemic, and the population enjoys a high degree of immunity.

Animals↗
PubMed1998

Multiple host-feeding and biting persistence of Aedes aegypti.

The effects of host activity, host defensive behaviour and biting persistence on multiple host-feeding by Aedes aegypti (L.) were investigated, in laboratory conditions, on human volunteers. In four different settings, four or five volunteer hosts displayed inactive, mildly active, mildly defensive and highly defensive behaviour. Into each of the four trials, each with 20 replicates, a single mosquito was released for a period of 10 min. In all settings, the median number of hosts sought per mosquito was constant, regardless of host activity and host defensive behaviour. Host defensive behaviour was thus not seen to exert a selective pressure on mosquitoes to abandon their hosts. No relationship was found between biting persistence and the number of hosts sought, indicating that biting persistence does not affect disease transmission. As one of the female hosts was consistently and significantly less attractive to host-seeking mosquitoes than any other volunteer in all four settings, it seems that some individuals are significantly less at risk from mosquito-borne pathogens than others.

Aedes↗
PubMed2006

Synthetic glycovaccine protects against the bite of leishmania-infected sand flies.

Leishmaniasis is a vectorborne disease transmitted to human and other mammalian hosts by sand fly bite. In the present study, we show that immunization with Leishmania mexicana promastigote secretory gel (PSG) or with a chemically defined synthetic glycovaccine containing the glycans found in L. mexicana PSG can provide significant protection against challenge by the bite of infected sand flies. Only the glycan from L. mexicana was protective; those from other species did not protect against L. mexicana infection. Furthermore, neither PSG nor the glycovaccine protected against artificial needle challenge, which is traditionally used in antileishmanial vaccine development. Conversely, an antigen preparation that was effective against needle challenge offered no protection against sand fly bite. These findings provide a new target for Leishmania vaccine development and demonstrate the critical role that the vector plays in the evaluation of candidate vaccines for leishmaniasis and other vectorborne diseases.

Animals↗
PubMed1997

Clinical manifestations of Plasmodium falciparum malaria experimentally induced by mosquito challenge.

To determine the characteristics of clinical illness accompanying Plasmodium falciparum infection induced by controlled exposure to infected mosquitoes, records of 118 volunteers participating in studies conducted between 1985 and 1992 were reviewed. One hundred fourteen volunteers (97%) reported at least one symptom attributable to malaria, with fatigue, myalgias or arthralgias, headache, and chills most commonly reported. The median duration of symptoms was 3 days. Fever was recorded in 61% of volunteers; 4 volunteers had temperatures >40 degrees C. Neutropenia and thrombocytopenia were present in 9% and 12% of volunteers, respectively. Despite counts as low as 658/microL (neutrophils) or 73,000/microL (platelets), no secondary infectious or hemorrhagic complications occurred. In all cases, volunteers recovered completely and laboratory values returned to baseline after specific antimalarial therapy. Recrudescence did not occur in any volunteer. In this model, mosquito inoculation of P. falciparum is a reliable, safe, and well-tolerated method of experimental challenge.

Adolescent↗
PubMed2001

Estimation of vectorial capacity of Anopheles dirus (Diptera: Culicidae) in a forest-fringed village of Assam (India).

To estimate the vectorial capacity of Anopheles dirus, the main vector of forest malaria in the northeastern region of India, in order to gain an understanding of entomological factors related to malaria transmission in forest-fringe areas of Assam, India, an isolated village in the tropical rain forest-fringed area in the district of Dibrugarh, Assam, under the influence of An. dirus alone was studied. Data on various entomological variables required for computation of the vectorial capacity were generated in each month from June 1999 to May 2000 in the field using standard techniques. Malaria prevalence was also studied during the same period in the study village and correlated with the estimated vectorial capacity of An. dirus. Vectorial capacity of An. dirus was highest, 0.779 for Plasmodium vivax (Pv) and 0.649 for Plasmodium falciparum (Pf), during the hot-monsoon season (June-September) and decreased to 0.08 (Pv) and 0.07(Pf) in the temperate postmonsoon season (October-November) before attaining zero values in the cool-dry season (December-February). With increasing temperature in the temperate premonsoon season (March-May), vectorial capacity recorded was 0.119 and 0.82 for Pv and Pf, respectively. Significant positive correlation was seen between the estimated vectorial capacity of An. dirus and the number of new Pf (r = 0.86, p < 0.001) and Pv (r = 0.69, p < 0.02) cases in the study village in different months. Thus, this study highlights the pattern of malaria transmission by An. dirus in a forest-fringe area of Assam that begins in March, peaks in July/August, subsides by November, and remains interrupted between December and February. Measures for controlling malaria in forest-fringe areas should be scheduled accordingly.

Animals↗
PubMed2003

Pre-West Nile virus outbreak: perceptions and practices to prevent mosquito bites and viral encephalitis in the United States.

Mosquitoes can transmit over 100 of the viruses that can cause encephalitis, meningitis, and hemorrhagic disease in humans (Chin 2000; Gubler 1996; Monath 1989). While much is known about the ecology, epidemiology, and clinical manifestations of the arboviral encephalitides (Campbell et al. 2002; Centers for Disease Control and Prevention 1997; Gubler 1998; Hayes 1989; Hubálek and Halouzka 1999), little empirical research exists regarding the U.S. population's knowledge of mosquitoes and arboviral encephalitis, particularly prior to the U.S. outbreak of West Nile virus (WNV) in 1999. A nationally representative 55-item survey instrument was successfully administered to 1,500 adults in the United States and an additional 250 adults in six states in the Northeast (Connecticut, Delaware, New Jersey, New York, Pennsylvania, and Rhode Island) regarding mosquitoes and mosquito-borne viral encephalitis. A summary outcome measure for mosquito bite prevention was created. Analyses revealed that the following were statistically significant predictors of behaviors taken to prevent mosquito bites: being concerned about being bitten by mosquitoes, perceived effectiveness of staying indoors in late afternoon and early evening was protective, perceived effectiveness that mosquito repellent is not harmful to health, owning dogs and/or cats as pets, being married, and being > or = 18-44 years old. Being concerned about being bitten by mosquitoes was the most robust predictor of behavioral action to prevent mosquito bites (OR = 7.3; 95% CI = 4.3, 12.2). Observed misperceptions and inadequate knowledge regarding insect repellents suggest increased promotion of the safety and efficacy of DEET-containing insect repellents is warranted.

Adult↗
PubMed2006

High prevalence of West Nile virus: a continuing risk in acquiring infection from a mosquito bite.

The prevalence of West Nile Virus (WNV) was evaluated by diplex real-time RT-PCR assay for the years 2001-2005 in Culex species of mosquitoes, several species of dead birds, and clinically suspected mammals collected in Kansas. The analysis was performed using a TaqMan-based diplex real-time RT-PCR assay targeted against two regions of the WNV genome, envelope glycoprotein gene and 3' untranslated region. The assay aided in the accurate detection of WNV in mosquitoes at high prevalence for the years 2002-2005. Similarly, high incidence of birds that tested positive for WNV was detected in 2002-2004. WNV positives in mammals by the diplex real time RT-PCR assay included horses, squirrels, mules, sheep and a mountain goat. Majority of the equine WNV positives were detected only in the year 2002. Sequence analysis of a segment of the envelope glycoprotein gene from 31 randomly selected WNV positive samples revealed variations in six samples at one or two nucleotide positions. The identity of high levels of WNV positives in Kansas parallels the recent reports on the widespread distribution of the virus in the United States. The continued detection of WNV in the mosquitoes is of significant public health concern and calls for continued surveillance and public health activities.

3' Untranslated Regions↗
PubMed1998

Control experiments with yellow jacket wasps (Hymenoptera: Vespidae) injuring cattle in Israel.

Injuries caused by the German yellow jacket Vespula germanica F. to dry and lactating dairy cows (Bos tourus) in 5 herds in Israel were monitored and adversely affected < or = 65% of the cows. Elimination of large alternative protein sources (placentas, sewage containing milk from the milking parlor), and prebaiting with high-quality minced meat (or fish) in adequate numbers of baiting cages around the dairy farm for several days, are necessary for successful control. Significant control was achieved after a shorter period of time when the dairy farm was surrounded by a smaller area of uncultivated land than by a larger area. At some dairy farms there were significant differences among numbers of wasps visiting the various cage sites and significant variability between baiting days. Efficient and significant control was achieved by minced meat bait containing 1.5% acephate (orthene) and 2% microencapsulated diazinon (Antikan). Wasps were totally repelled by minced meat bait containing 2.25% of a plant-derived bioinsecticide derived from Meliaceae (Ag1000). The potential of using Ag 1000 for repelling yellow jackets from teats and udders of dairy cows is discussed.

Animals↗