Analysis of survival data for <i>Simulium damnosum</i> using the regression method

Saporu, F. W. O.

doi:10.1080/00034983.1993.11812811

Cited by 2 publications

(4 citation statements)

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“…Additionally, Plasmodium -density dependent mortality has the potential to explain the low oocyst loads found in the field as those mosquitoes with large numbers of oocysts may have died as a result of infection as well as, or because of an interaction with, environmental factors. Density-dependent, parasite-induced vector mortality has been reported in other vector-borne diseases, and particularly in the filarial parasites, both in captivity [55,78,79] and in the field [80,81]. …”

Section: Discussionmentioning

confidence: 99%

Anopheles mortality is both age- and Plasmodium-density dependent: implications for malaria transmission

Dawes

Churcher

Zhuang

et al. 2009

Malar J

118

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BackgroundDaily mortality is an important determinant of a vector's ability to transmit pathogens. Original simplifying assumptions in malaria transmission models presume vector mortality is independent of age, infection status and parasite load. Previous studies illustrate conflicting evidence as to the importance of Plasmodium-induced vector mortality, but very few studies to date have considered the effect of infection density on mosquito survival.MethodsA series of three experiments were conducted, each consisting of four cages of 400-1,000 Anopheles stephensi mosquitoes fed on blood infected with different Plasmodium berghei ookinete densities per microlitre of blood. Twice daily the numbers of dead mosquitoes in each group were recorded, and on alternate days a sample of live mosquitoes from each group were dissected to determine parasite density in both midgut and salivary glands.ResultsSurvival analyses indicate that mosquito mortality is both age- and infection intensity-dependent. Mosquitoes experienced an initially high, partly feeding-associated, mortality rate, which declined to a minimum before increasing with mosquito age and parasite intake. As a result, the life expectancy of a mosquito is shown to be dependent on both insect age and the density of Plasmodium infection.ConclusionThese results contribute to understanding in greater detail the processes that influence sporogony in the mosquito, indicate the impact that parasite density could have on malaria transmission dynamics, and have implications for the design, development, and evaluation of transmission-blocking strategies.

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Section: Discussionmentioning

confidence: 99%

Anopheles mortality is both age- and Plasmodium-density dependent: implications for malaria transmission

Dawes

Churcher

Zhuang

et al. 2009

Malar J

118

View full text Add to dashboard Cite

show abstract

“…In estimating the survival function in mosquitoes we have used the human Mf-density as a factor and the parasite load in dead mosquitoes as a covariate. Instead, an estimate of the Mf-uptake (obtained by dissecting a sample of mosquitoes) could have been used as a co-variate or a factor as had been done for the onchocerciasis vector S. damnosum (Saporu, 1993). We consider that this would lead to problems in accuracy of the estimation of survival function because the validity of an estimate of the Mf-uptake depends on the number of mosquitoes dissected.…”

Section: Methodological Issuesmentioning

confidence: 99%

“…As a consequence of parasite-induced reductions in survival, the lifeexpectancy of infected mosquitoes was reduced significantly with increasing number of parasites acquired, leaving less chance to transmit infection. Saporu (1993) by fitting both the Cox's proportional hazard model, and the Weibull accelerated failure time model to survival times of the onchocerciasis vector, Simulium damnosum, showed that a higher Mf-uptake reduced the survival of vector by a factor of 1 . 3 times compared to normal fly.…”

Section: Mosquito Survival and Life-expectancymentioning

confidence: 99%

“…The main mechanisms proposed to drive limitation are increased mortality of the larvae (loss of parasites) and parasite-induced vector mortality particularly at high parasite densities (Brengues & Bain, 1972 ;Subramanian et al 1994 ;Das et al 1995 ;Dye & Williams, 1995). Both experimental studies (Crans, 1973 ;Maeda & Kurihara, 1980 ;Saporu, 1993 ;Failloux et al 1995 ;Subramanian et al 1998) and field studies (Samarawickrema & Laurence, 1978 ;Subramanian et al 1994) found excess-mortality among heavily infected mosquitoes. In field studies, it is difficult to distinguish the effect of vector-age from the effect of parasite burden on the survival of mosquitoes because the wild population is a mixture of members with different ages.…”

Section: Introductionmentioning

confidence: 99%

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Vector survival and parasite infection: the effect of Wuchereria bancrofti on its vector Culex quinquefasciatus

et al. 2004

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This paper investigates a cohort of 2187 laboratory reared Culex quinquefasciatus fed on 69 human volunteers, including 59 persons with different levels of Wuchereria bancrofti microfilariae and 10 without microfilaria. Mosquitoes were followed until death. Mosquito survival was analysed in relation to the level of microfilaria in the human and larval count in the dead mosquito. Vector mortality during the extrinsic incubation period (12 days post-engorgement) was significantly higher in mosquitoes fed on microfilaraemic volunteers (50%) than in those fed on amicrofilaraemics (29%). Both the percentage infected and the geometric mean parasite density was significantly higher among mosquitoes which died before 13 days (45% infected and 10 larvae per infected mosquito) than those surviving beyond 13 days (39% and 2.2), suggesting a parasite loss of more than 80% during the extrinsic incubation period. A large proportion (62%) of the mosquitoes that died during the early of phase of parasite development were infected (36% in low, 26% in medium and 90% in high human Mf-density). Survival analysis showed that the parasite load in mosquitoes and the human Mf-density for a given parasite load are independent risk factors of vector survival. Overall, the hazard of dying was found to be 11-15 times higher among mosquitoes fed on microfilaraemic volunteers than those fed on amicrofilaraemics. The hazard doubles for every increase of about 60-70 parasites in the vector. As a consequence of the parasite-induced reduction in vector survival, the transmission success of the parasite is reduced. The implication of the results on control/elimination of lymphatic filariasis using mass-drug administration is discussed.

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Analysis of survival data for Simulium damnosum using the regression method

Cited by 2 publications

References 5 publications

Anopheles mortality is both age- and Plasmodium-density dependent: implications for malaria transmission

Anopheles mortality is both age- and Plasmodium-density dependent: implications for malaria transmission

Vector survival and parasite infection: the effect of Wuchereria bancrofti on its vector Culex quinquefasciatus

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