Chemical ecology of the behaviour of the filariasis mosquito Culex quinquefasciatus Say

Culex quinquefasciatus is an important vector of urban bancroftian filariasis in the tropical world. Despite its public health importance, much of its olfactory mediated behaviour is poorly understood. Studies on resource-location behaviour, in particular the role of semiochemicals in its behaviour, are required to understand the relationship between the mosquito, its host and the surrounding environment to effectively control bancroftian filariasis. In this thesis the role of semiochemicals in the host-location behaviour and oviposition site-selection of Cx quinquefasciatus has been examined.The olfactory responses of the host-seeking female Cx quinquefasciatus to various odour stimuli in a dual-choice olfactometer showed that the mosquito responds more to foot skin emanations than to carbon dioxide and moisture. These results present evidence that kairomones used during the host-seeking process by Cx quinquefasciatus are present in human skin emanations. The preference of Cx quinquefasciatus between humans, and domestic animals, was investigated in the field. The response of the mosquito to the humans, cattle and goats was also compared to its response to carbon dioxide. The mosquito responded to human olfactory cues in significantly larger numbers than to the calf or goat cues. The response of the mosquito to either the calf or goat was similar.It can be concluded that with equal availability of the three vertebrates, Cx quinquefasciatus would respond significantly more to cues from human hosts than from either a calf or a goat. The major olfactory cue from goat or a calf, to which this mosquito responds is probably carbon dioxide. Furthermore, the response of Cx quinquefasciatus, Anopheles gambiae s.l. and An. funestus to human odour was compared with that to carbon dioxide in the field. Human odour attracted a larger number of host-seeking Cx quinquefasciatus, An. gambiae and An. funestus than carbon dioxide.In an indoor situation human body odour other than carbon dioxide is the principal cue to which these mosquito species respond and that the physical cues from a host and carbon dioxide, when used as a kairomone on its own, account for a minor part of the overall attractiveness of man. Skin emanations and various specific organochemical compounds known to attract other blood sucking Diptera were tested for Cx quinquefasciatus in the field. It was found for the first time that Cx quinquefasciatus can be trapped into traps baited with human skin residues. Furthermore a larger number of Cx quinquefasciatus were caught in traps baited with carbon dioxide than in traps baited with either acetone, octenol or butyric acid. The combination of carbon dioxide and skin emanations resulted in an additive effect. These results indicate that under field conditions Cx quinquefasciatus can be sampled by traps baited with skin emanations and/or carbon dioxide.As far as the odour-mediated oviposition behaviour is concerned it was found that the oviposition by Cx quinquefasciatus occurs more frequently in the presence of the mosquito oviposition pheromone and/or skatole than in plain water. The daily oviposition rhythm of Cx quinquefasciatus showed two peaks, the higher at twilight and the lower peak at dawn. The biological activities of the synthetic oviposition pheromone (acetoxyhexadecanolide) and skatole were found to last for over 9 and 7 days respectively.It was further found that the combination of synthetic oviposition pheromone and soakage pit water or grass infusions resulted in a synergistic response in the oviposition by Cx quinquefasciatus, Cx cinereus and Cx tigripes. However, a blend of synthetic oviposition pheromone and skatole resulted into an additive oviposition response by Cx quinquefasciatus . Oviposition semiochemicals can thus be used as ovitraps or gravid mosquito traps to monitor Cx quinquefasciatus populations or to attract mosquitoes to sites treated with a biopesticide for vector control.The efficiency of various odour baited sampling devices was also investigated. It was found that the efficiency of the widely used Centers for Disease Control (CDC) light trap in sampling an indoor population of Cx quinquefasciatus and An. gambiae is affected by the position of the trap in relation to the human-baited bed net. 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 bed net. Parity rates were significantly higher near the top of the net than at the level of the host. In addition, infective Cx quinquefasciatus were caught in the trap positioned above the foot-end of the bed net.Various trapping systems baited with carbon dioxide were compared in sampling outdoor populations of An. gambiae and Cx quinquefasciatus . The efficiency of the Counterflow Geometry (CFG) trap was similar to that of electric nets (ENT). Both CDC traps with light or without light were less efficient in collecting An. gambiae or Cx quinquefasciatus outdoors. It is possible, therefore, to collect the two mosquito species outdoors with CFG traps or ENT baited with carbon dioxide. Finally an assessment of traps baited with oviposition semiochemicals in sampling of gravid Cx quinquefasciatus is reported. A CFG trap baited with either a synthetic oviposition pheromone, grass infusions or the combination of the two was found to be a useful tool for collecting gravid Cx quinquefasciatus both indoors and outdoors. However, the proportion of gravid mosquitoes in the catches increased when the traps were placed away from mosquito emergence sites. In conclusion, the study shows that chemical ecology plays a significant role in the life cycle of Cx quinquefasciatus and this principle can be used to develop new control strategies.</p

Mosquito Net Coverage and Utilisation for Malaria\ud Control in Tanzania\ud

\ud In recent years malaria parasites have developed resistance to the most commonly used antimalarial drugs in Tanzania, posing a major challenge for its control. This has led to frequent changes of malaria treatment guidelines, more recently to expensive, yet more effective arthemether/lumefantrine. The use of insecticide treated mosquito nets (ITNs) and long lasting nets (LLINs) in Tanzania has increased slowly over the past few years. Despite the introduction of a voucher scheme to the vulnerable groups, the proportion of households with at least an ITN/LLIN in the country has not been able to achieve the Abuja Declaration of 60% net coverage. Statistics available on the utilisation of nets do not provide a good estimate of the coverage, because of the different study design used to collect the information. This survey was carried out in 21 districts of Tanzania to determine the coverage and utilisation of insecticide treated nets to provide baseline information of the net requirement to cover every sleeping bed in the country. Specifically, this study aimed to (i) determine the ITN coverage by and its distribution in the country; and (ii) determine knowledge, attitudes and practice of the householders as regards to malaria prevention and control Twenty one districts (one from each region) of Mainland Tanzania were selected for the survey. Selection of the district was random. In each district, two wards were selected, one urban (within the district capital) and one rural or sub‐urban. Households were selected randomly using a table of random numbers. At household level, the head or any adult who represented the head of household was interviewed. A structured pre‐tested questionnaire was used to collect information on knowledge, attitude and practices in malaria control, with emphasis on mosquito net ownership and utilisation. Of the 9549 targeted households, 9166 (96%) participated in the survey. Majority of the respondents (76.8%) were from rural district.The mean household size was 3.9 persons. On average, children <5 years old accounted for 39.3% of the members of the households. Respondents with no formal education accounted for 15.8‐37.4% of the interviewees. Most of them were from Mkuranga (55%), Kigoma‐Ujiji (44.2%) and Newala (37.9%). High literate rates were observed in Arumeru and Moshi districts. The majority of the respondents knew that the mosquito is the vector of the malaria parasite (92.6‐99.4%) and infection is through a mosquito bite (92.7‐99.8%). The knowledge of respondents on malaria transmission was generally high (94.0‐99.0%). The majority of the respondents (95.2%) considered the use of mosquito nets as the most effective way of malaria prevention. However, of these, only 66.7% said to have actually used nets in their life time. Knowledge on the use of mosquito nets in the control of malaria was highest and lowest in Eastern and Central zones, respectively.\ud Seventy‐seven percent (4457/8933) agreed to have the investigator entry into their houses and verify the\ud number of nets owned. On average, 62.9% (5,785/8933) of the households had at least a mosquito net. Majority of the respondents in Northern (76.5%) and Southern (76.5%) zones owned at least a mosquito net. The lowest mosquito net ownership was observed among respondents in Western Zone (39.6%). District‐wise, net ownership was highest in Lindi (94.5%), Kyela (91.3%) Arumeru (86.1%), Ilala (83.1%)\ud and Nyamagana (80.0%). Ownership of net was very low in Kilolo (34.8%), Kigoma (36.5%) and Musoma Rural (41.3%). Of the households with nets, 74.4% were using nets all year round. A larger proportion of respondents in Kilolo (68.5%), Mpwapwa (51.9%), Songea Rural (49.2%) and Shinyanga Rural (46.3%) were only using the nets during the rainy season. Out of 9,166 households visited, 3,610 (39.3%) had at least one under five child. Of these, in 1,939 (53.7%) of the households the child slept under a mosquito net during the previous night. Use of nets in children <5 years was most common in northern zone (74%); followed by eastern (66.9%) and southern zone (61.1%). Districts with the largest proportion of <5 year children sleeping under a mosquito nets were Lindi (90.0%), Kyela (85.2%), Ilala (83.2%) and Arumeru (78.2%). Only about a quarter (27%) of the children <5% in western zone were sleeping under a mosquito net. Lowest net coverage for <5 year was in Kigoma (22.7%), Kilolo (25%) and Bukoba Rural (31.2%). A total of 5,785 (62.9%) owned at least a mosquito net. Of these, 4,219 and 1,566 were from the rural and urban districts, respectively. More households in the urban districts (73.4%) than rural districts (59.7%) owned at least a mosquito net. Likewise, there were more households (64.9%) in the urban districts with <5years children sleeping under mosquito nets than in the rural districts (50.4%). More households in urban (32.8%) than in rural districts (25.1%) had at least one insecticide treated net. The number of households with mosquito nets enough for all members of the households ranged from 18.9% (in Urambo) to 37.4% (in Hanang). Households with at least 50% or more occupants using mosquito nets ranged from 16.4% (in Urambo) to 42.8% (in Arumeru). Districts with the largest proportion of ≥50% of the household members sleeping under mosquito nets were Arumeru (46.9%) and Lindi (46.7%). In Manyoni and Lindi, 3.1% and 5% of the households were found to have more nets than the number of household occupants. Only 9% (801/9196) of the households had all occupants sleeping under a mosquito net. Kyela district had about a quarter (23.9%) of the households with all occupants sleeping under nets. Only 29% of the households had at least one insecticide treated mosquito nets. All nets in 51.4% of the households surveyed were ITNs. The largest proportion of households with ITN was observed in northern zone (40.2%), with Arumeru (46%) and Hanang (44.1%) districts having the highest ITN coverage. The lowest proportion (15.5%) of households with ITN was found in the Western Zone. Districts which had the lowest ITN coverage were Musoma Rural (12.6%), Kigoma‐Ujiji (13.2%), and Shinyanga Rural (14.4%). On average, 90.7% (8,123/8,953) of the respondents would prefer using ITN than having their house sprayed with long lasting residual insecticide. More households in urban (32.8%) than in rural districts (25.1%) had at least an ITN> A total of 1939 children underfives were sleeping under mosquito net (any type). Of these, 1140 (58.8%) were using insecticide treated nets (ITN). Overall, 31.6% of the underfives slept under an insecticide treated net during the previous night. Highest coverage was reported in Kyela (47.7%), Nyamagana (47.7%) and Arumeru (46.4%). Lowest ITN in underfives was reported in Kigoma‐Ujiji (16.0%), Musoma (17.2%) and Urambo (17.7%). In Songea more underfives children were sleeping under ITN (43.6%) than in untreated nets (40.9%). Control of bedbugs, lice, fleas, mites and cockroaches was the major added advantage of using insecticide treated nets. On average, 30.8% and 19.6% of the respondents mentioned cockroach and bedbug control as the main advantage of using ITN, respectively. The majority (52.9%) preferred blue coloured net (Northern=45.6%; Central=59.2%; Eastern=56.4%; Lake= 54.4%; Southern= 60.3%, Western= 58.5%) and Southern Highlands= 49.1%). Other colour preferences were white (29.6%), green (14.1%), black (2.1%) and pink (1.2%). A strong preference for blue mosquito nets was observed among respondents in Musoma (77.3%) and Newala (75.5%) districts. On the other hand, the weakest preference (24.7%) for blue nets was observed among respondents in Arumeru district. The majority of the respondents (82%) preferred rectangular shaped net. A larger percent (61.8%) the respondents preferred to have the map of Tanzania as a national logo to identify nets distributed in the country. On average, 62.7% and 28.8% of the households in Tanzania own at least one mosquito net (any type) and insecticide treated net, respectively. Tanzania expects that ITN coverage of under fives in 2009, after the Under Five Catch‐up Campaign is complete, to be at least 80%. If this is to be achieved, there is a need for concerted effort in scaling up the distribution and demand for long lasting nets throughout the country. Moreover, the planned use of IRS in malaria control, currently considered unpopular should be accompanied by rigorous community health education to avoid resistance from household members.\u

The response of Culex quinquefasciatus (Diptera: Culicidae)to traps baited with carbon dioxide, 1-octen-3-ol, acetone, butyric acid and human foot odour in Tanzania

The responses of Culex quinquefasciatus Say to traps baited with carbon dioxide, 1-octen-3-ol, acetone, butyric acid and human foot odour were studied in the field in Muheza, north-east Tanzania using Counterflow Geometry (CFG) and Centers for Disease Control (CDC) traps. It was found that significantly more C. quinquefasciatusresponded to foot odour collected on nylon stockings than to clean nylon stockings (P 0.05). These results indicate that the Afrotropical C. quinquefasciatusrespond significantly better to traps baited with carbon dioxide than to either octenol, acetone or butyric acid, and that human foot odour contains stimuli to which C. quinquefasciatus is attracted under field conditions

Indoors man-biting mosquitoes and their implication on malaria transmission in Mpwapwa and Iringa Districts, Tanzania

Entomological surveys were carried out in six villages at different altitudes in Mpwapwa and Iringa Districts in central Tanzania in March 2002. A total of 1291 mosquitoes were collected. Of these, 887 mosquitoes were collected by light traps and 404 by indoor pyrethrum spray catch technique. Seventy-nine percent (1026) were Anopheles gambiae   s.l., 0.2% (N= 3) were An. funestus, and 20.3% (N= 262) were Culex quinquefasciatus   . Other species including Cx cinereus, An. coustani and Aedes   spp accounted for 0.5% of the mosquito population. In Iringa, more mosquitoes were collected by pyrethrum spray catch than light trapping technique. The light trap catch: spray catch ratio in Iringa and Mpwapwa was 1:1.15 and 2.5:1, respectively. Indoor pyrethrum spray catch gave an overall estimate of An. gambiae density of 8 and 0.6 mosquitoes per room in Iringa and Mpwapwa, respectively, whereas light trap collections gave an overall respective density of An. gambiae of 63.9 and 2.9 mosquitoes per room. The densities of house entering mosquitoes were found to range from 0 to 135 in Iringa and from 2.6 to 3.5 per room in Mpwapwa. An. funestus mosquitoes were collected in Iringa only. None of the dissected An. gambiae collected in the two districts was infected with malaria sporozoites. Despite low mosquito densities and absence of infective mosquitoes in our study, the two districts are malaria epidemic prone, thus a continuous surveillance is critical for a prompt response to any impending outbreak. Further longitudinal studies are required to determine the transmission potential of the malaria mosquitoes in the two districts

Strategic approach for strengthening national and regional disease surveillance System: The East African example

No Abstract Availabl