PubMed Health⌕ Search

Biomedical subjects

B G Knols

Publications and source records attributed to B G Knols.

17 recordsLinked to original sources
PubMed2000

Plasmodium falciparum sporozoites increase feeding-associated mortality of their mosquito hosts Anopheles gambiae s.l.

There is some evidence that pathology induced by heavy malaria infections (many oocysts) increases mortality of infected mosquitoes. However, there is little or no published evidence that documented changes in feeding behaviour associated with malaria infection also contribute to higher mortality of infected mosquitoes relative to uninfected individuals. We show here for the first time that, in a natural situation, infection by the sporozoites of the malaria parasite Plasmodium falciparum significantly reduced survival of blood-feeding Anopheles gambiae, the major vector of malaria in sub-Saharan Africa. To estimate feeding-associated mortality of infected mosquitoes, we compared the percentage of sporozoite infection in host-seeking mosquitoes caught before and after feeding. The infection rate was 12% for mosquitoes caught during the night as they were entering a tent to feed; however, only 7.5% of the surviving members of the same cohort caught after they had had the opportunity to feed were infected. Thus, Plasmodium falciparum sporozoites increased the probability of dying during the night-time feeding period by 37.5%. The increase in mortality was probably due to decreased efficiency in obtaining blood and by increased feeding activity of the sporozoite-infected mosquitoes that elicited a greater degree of defensive behaviour of hosts under attack.

Animals↗
PubMed1999

Infochemicals in mosquito host selection: human skin microflora and Plasmodium parasites.

The interaction between the African malaria vector Anopheles gambiae and its human host has traditionally been viewed within a bitrophic context, considering only the human and the mosquito. Recently, the influence of the Plasmodium parasite on the interaction has been recognized, because it affects the physiology and/or behaviour of humans and mosquitoes. However, studies on odour-mediated host-seeking behaviour of An. gambiae and other Diptera have provided evidence that a fourth group of organisms should be taken into consideration. Human skin microflora play a role in the production of odorous compounds that might function as kairomones for mosquitoes. Here, Marieta Braks, Rob Anderson and Bart Knols introduce the role of human microflora into the process of odour-mediated host selection and review the interaction in a multipartite context so as to identify research avenues that will enhance our limited knowledge of this aspect of malaria transmission.

Animals↗
PubMed1999

Odor-mediated behavior of Afrotropical malaria mosquitoes.

The African mosquito species Anopheles gambiae sensu lato s.l. and Anopheles funestus rank among the world's most efficient vectors of human malaria. Their unique bionomics, particularly their anthropophilic, endophagic and endophilic characters, guarantee a strong mosquito-host interaction, favorable to malaria transmission. Olfactory cues govern the various behaviors of female mosquitoes and here we review the role of semiochemicals in the life history of African malaria vectors. Recent evidence points towards the existence of human-specific kairomones affecting host-seeking A. gambiae s.l., and efforts are under way to identify the volatiles mediating this behavior. Based on examples from other Culicidae spp., it is argued that there is good reason to assume that mating, sugar feeding, and oviposition behavior in Afrotropical malaria vectors may also be mediated by semiochemicals. It is foreseen that increased knowledge of odor-mediated behaviors will be applied in the development of novel sampling techniques and possibly alternative methods of intervention to control malaria.

Africa↗
PubMed1998

Short report: Influence of centers for disease control light trap position, relative to a human-baited bed net, on catches of Anopheles gambiae and Culex quinquefasciatus in Tanzania.

The best position for Centers for Disease Control (Atlanta, GA) light traps, in relation to human-occupied bed nets for trapping of host-seeking Anopheles gambiae Giles and Culex quinquefasciatus Say mosquitoes, was determined in Tanzania. Significantly higher catches were recorded for both species when the trap was positioned at the foot end of the bed, near the top of the net. Parity rates were significantly higher near the top of the net than at the level of the host. Since trap position affects the catch size and the proportion of infectious mosquitoes therein, standardized use of this sampling technique for estimating entomologic inoculation rates (i.e., the number of potentially infectious bites received over a certain period of time) is recommended.

Animals↗
PubMed1998

Olfactory responses of female Culex quinquefasciatus Say (Diptera: Culicidae) in a dual-choice olfactometer.

Olfactory responses of individual female (n = 1010) Culex quinquefasciatus Say (Diptera: Culicidae) to various odor stimuli were studied in a dual-choice olfactometer. Responses (i.e., the number of mosquitoes entering either of both olfactometer ports) were studied towards clean conditioned air (control), human foot skin emanations (collected on worn stockings), carbon dioxide (4.5% in clean air), moistened air, and various combinations thereof. Skin emanations were significantly more attractive (chi 2 = 23.0, p < 0.001) than clean stockings (control). The mosquito was also significantly more attracted (chi 2 = 7.7, p < 0.01) to skin emanations than to a clean stocking to which water (an equivalent of that absorbed by a worn stocking) was added. A moistened (1 g H2O) clean stocking, however, was slightly more attractive than a dry stocking (chi 2 = 6, p < 0.025). Carbon dioxide (4.5%) did not elicit higher responses than clean air, and no synergistic effect was observed in combination with skin emanations. With the aim of developing an odor-baited trap, our results indicate that Cx. quinquefasciatus responds well to human body odors which can be collected on polyamide materials.

Animals↗
PubMed1996

Selection of biting sites by mosquitoes.

Most blood-feeding arthropods feed at specific sites on their hosts. There can be many reasons for such non-random distributions and not all of them are related to active selection of feeding sites by the parasites. Observations of mosquito biting on humans revealed that most species have preferred biting sites and that not all species share the same preferences. The selection of these sites may be related to several factors, depending on the mosquito species, which include the visual and chemical properties of the host. Identification of these factors can provide us with information on cues that are important in the finding and selection of a host. The choice of biting sites can be influenced by host-related cues of varying specificity. Therefore, it can in some cases reflect the host range of the mosquito species.

Animals↗
PubMed1996

Limburger cheese as an attractant for the malaria mosquito Anopheles gambiae s.s.

In the process of bloodfeeding, female Anopheles can transmit malaria parasites to humans. At night, while searching for blood, these insects respond to visual, physical and chemical properties of humans. Current research concentrates on the identification of kairomones, which guide mosquitoes to humans. Earlier observations on the biting behaviour of Anopheles gambiae s.s. on humans have now resulted in the discovery of a remarkable attractant for this important malaria vector, and it is thought that this will accelerate the development of odour-baited traps for malaria mosquito surveillance and control in sub-Saharan Africa, as discussed here by Bart Knols and Ruurd De Jong.

Journal Article↗
PubMed1995

Selection of biting sites on man by two malaria mosquito species.

While searching for blood, female mosquitoes pass through a behavioural process involving responses to visual, physical and chemical properties of the host. Temperature and humidity are thought to dominate mosquito orientation near the host. We observed that biting of two malaria mosquito species, i.e. Anopheles atroparvus (van Thiel) and Anopheles gambiae s.s. (Giles) preferentially occurs on different body regions of a naked motionless human host. Their preference for the head and foot regions respectively correlated with particular combinations of skin temperature and eccrine sweat gland density. Subsequent modification of the host's odour profile by removing exhaled breath and washing feet results in significant changes of these preferences.

Animals↗
PubMed1994

Influence of human breath on selection of biting sites by Anopheles albimanus.

The selection of biting sites by Anopheles albimanus on a human host was studied in the laboratory. The perception of exhaled breath guided the mosquitoes towards the head region, and was associated with a preference (P < 0.001) for biting this part of the body. Subsequent removal of breath resulted in a strong reduction of the number of bites on the head (from 49 to 20%). The significance of these findings in relation to host location is discussed.

Adult↗
PubMed1993

A trial to control the tsetse fly, Glossina morsitans centralis, with low densities of odour-baited targets in west Zambia.

A large-scale trial investigated the possibility of eradicating G.m.centralis from a traditional cattle rearing area using odour-baited targets at a reduced overall target density from 4 to 0.5-2.3 per km2, thus cutting down initial material costs by about 50%. Only the periphery of what was thought to be prime tsetse habitat (dense woodland) was treated with targets. These were all black or blue/black cloth (1.8 x 1 m), sprayed with deltamethrin suspension concentrate and baited with butanone and/or acetone (40-130 mg/h) and 1-octen-3-ol (0.5 mg/h). Although fly catches from traps and flyrounds initially dropped by approximately 3% per day and trypanosomiasis cases declined by 99% within a year, eradication was not achieved, so that more targets were deployed at a later stage. Although initially cheaper, the option of using reduced target densities proved financially unattractive because of prolonged periods of target maintenance prior to eradication. Revised strategies for tsetse control with odour-baited, insecticide-impregnated targets in west Zambia are presented.

Acetone↗
PubMedDate not supplied

Differential attractiveness of isolated humans to mosquitoes in Tanzania.

Individually occupied tents, modified for sampling mosquitoes, were used to assess the attractiveness of 3 humans for Anopheles gambiae Giles s.l., A. funestus Giles, Culex quinquefasciatus Say and Mansonia spp. in north-east Tanzania. Significant differences (P < 0.025) in attractiveness were observed for the first 3 species, whereas Mansonia did not show any preference. Because of the objective sampling method used, these results provide the first conclusive evidence that isolated people vary in attractiveness to mosquitoes.

Adult↗