Laboratory observations were made on the uptake of microfilariae (mf) of Wuchereria bancrofti by Anopheles gambiae, An. arabiensis, An. merus and An. funestus. Over host mf densities ranging from 450/ml to 1735 mf/ml neither the percentage of mosquitoes ingesting mf nor the mean number of mf per mosquito was correlated to host mf density. All mosquito species damaged mf during ingestion but the proportion harmed was independent of host mf density. The mean proportion damaged was 0.67 in An. gambiae, 0.51 in An. merus, 0.47 in An. Arabiensis and 0.26 in An. funestus. A comparison of the mean number of undamaged mf ingested and the number of larvae in the thoracic muscles revealed that not all undamaged mf were able to reach the thoracic muscles.

Africa, Eastern↗

PubMedDate not supplied

Factors affecting transmission of Wuchereria bancrofti by anopheline mosquitoes. 4. Facilitation, limitation, proportionality and their epidemiological significance.

Quantitative understanding of the transmission dynamics of lymphatic filarial parasites is essential for the rational planning of control strategies. One of the most important determinants of transmission dynamics is the relationship between parasite yield, the success rate of ingested microfilariae (mf) becoming infective larvae in a mosquito vector, and mf density in the source of the human blood meal. Three types of relationship have been recognized in human filaria/mosquito couples--limitation, facilitation and proportionality; facilitation has hitherto been observed only in the couple Wuchereria bancrofti/Anopheles gambiae in Burkina Faso, in experimental studies on a high density mf carrier. The present paper demonstrates facilitation in W. bancrofti/An. gambiae and W. bancrofti/An. arabiensis in lower mf density carriers in The Gambia and Tanzania, and in W. bancrofti/An. funestus in Tanzania. Facilitation was not found in An. melas in The Gambia nor in An. merus in Tanzania. Analysis of published data shows limitation at low level mf densities in W. bancrofti/Culex quinquefasciatus in Sri Lanka, and in the same couple in India. Limitation also occurs in Brugia malayi/Aedes togoi in experimental cats; proportionality occurs in B. malayi/Mansonia bonneae in Malaysia. The epidemiological significance of these host/parasite relationships is discussed, and supporting evidence for its validity is presented from the published results of large-scale control programmes.

Animals↗

PubMedDate not supplied

The potential of ivermectin to control the malaria vector Anopheles farauti.

We investigated mortality in Anopheles farauti mosquitoes, a major coastal malaria vector in the south-west Pacific, fed on a volunteer who had taken a 250 micrograms/kg dose of ivermectin. High mortality was recorded in mosquitoes feeding during the first week after treatment of the volunteer, for instance 100-80% failed to survive 3 days. A long-term residual effect of ivermectin in the blood was indicated by a small but significantly higher mortality in mosquitoes fed 6 weeks after ivermectin was taken. These effects were included in malaria transmission models that incorporated host choice and host-induced mortality parameters. For the zoophilic An. farauti, ivermectin treatment of animals resulted in a greater reduction in malaria than ivermectin treatment of humans alone, whereas for an anthropophilic vector, treatment of humans was more important. This suggests that ivermectin treatment of animals could have an important role in malaria control where An. farauti is the vector. Improvement in the health of humans and domestic animals through control of parasitic worms and mites might encourage community participation in strategies involving ivermectin.

Animals↗

PubMedDate not supplied

Host-dependent Anopheles flavirostris larval distribution reinforces the risk of malaria near water.

Malaria control strategies are more likely to be successful if groups at high risk can be accurately predicted. Given that mosquitoes have an obligate aquatic phase we were interested in determining how vector larval abundance relates to the spatial distribution of human malaria infection. We examined the relationship between malaria parasite prevalence and distance from vector larval habitat, and vector larval abundance and distance from human habitation, in separate studies in rural, low-endemic areas of the Philippines. Parasite prevalence among symptomatic patients was significantly higher among those living in proximity (< or = 50 m) to potential larval habitats of the major vector, Anopheles flavirostris (adjusted odds ratio [AOR] = 2.64, P = 0.02 and AOR = 3.43, P = 0.04). A larval survey of A. flavirostris revealed a higher density of early and late instars near human habitation (adjusted P < 0.05). The results suggest that larvae are associated with human habitation, thereby reinforcing malaria risk in people living close to larval habitats. This has implications for understanding the interaction between vectors, hosts, and parasites, and the potential for success of localized malaria control measures.

Animals↗

PubMedDate not supplied

Linkage study on dieldrin resistance and an inversion on the second chromosome of Anopheles stephensi.

In a study on the linkage between the gene for dieldrin resistance and an inversion on the second chromosome in Anopheles stephensi, the two factors were found to assort independently. As dieldrin resistance can be assigned either to the third chromosome, or to a position on the second chromosome more than 50 cross-over units from the inversion.

Animals↗

PubMedDate not supplied

Adult behaviour of members of the Anopheles gambiae complex in the Gambia with special reference to An. melas and its chromosomal variants.

Polytene chromosome studies on the member species of the Anopheles gambiae complex in The Gambia and surrounding areas in Senegal led to comparative observations on bionomics of sympatric populations of An. melas and An. gambiae. Moreover, inversion polymorphisms have been analyzed in An. melas and their possible relationships with behavioural variations in endophily and anthropophily have been considered. An. melas shows a remarkably short dispersal from typical larval breeding places associated with mangrove swamps and it is definitely more zoophilic and exophilic than An. gambiae. Only a very small fraction of An. melas biting outdoor on animals rests indoors and consequently the human blood index is largely overestimated if based on the examination of house samples alone. Differences in the frequencies of 2Rn inversion karyotypes of An. melas were observed between parallel samples obtained from animal shelters and houses, from night catches on man outdoor and from night catches on main indoor and on animal outdoor. Further differences were shown by blood meal identification between human and animal fed subsamples from the same house resting samples. Non-uniform feeding and/or resting behaviour between carriers of alternative 2Rn inversion karyotypes is postulated to explain these data.

Animals↗