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Zooprophylaxis or zoopotentiation: the outcome of introducing animals on vector transmission is highly dependent on the mosquito mortality while searching.

Saul A - Malar. J. (2003)

Bottom Line: Changing the accessibility of the humans had a much greater effect.Estimates of searching-associated vector mortality are essential before the effects of changing animal husbandry practices can be predicted.With realistic values of searching-associated vector mortality rates, zooprophylaxis may be ineffective.

View Article: PubMed Central - HTML - PubMed

Affiliation: Malaria Vaccine Development Unit, NIAID, NIH, Rockville, MD 20852, USA. ASaul@niaid.nih.gov

ABSTRACT

Background: Zooprophylaxis, the diversion of disease carrying insects from humans to animals, may reduce transmission of diseases such as malaria. However, as the number of animals increases, improved availability of blood meals may increase mosquito survival, thereby countering the impact of diverting feeds.

Methods: Computer simulation was used to examine the effects of animals on the transmission of human diseases by mosquitoes. Three scenarios were modelled: (1) endemic transmission, where the animals cannot be infected, eg. malaria; (2) epidemic transmission, where the animals cannot be infected but humans remain susceptible, e.g. malaria; (3) epidemic disease, where both humans and animals can be infected, but develop sterile immunity, eg. Japanese encephalitis B. For each, the passive impact of animals as well as the use of animals as bait to attract mosquitoes to insecticide was examined. The computer programmes are available from the author. A teaching model accompanies this article.

Results: For endemic and epidemic malaria with significant searching-associated vector mortality, changing animal numbers and accessibility had little impact. Changing the accessibility of the humans had a much greater effect. For diseases with an animal amplification cycle, the most critical factor was the proximity of the animals to the mosquito breeding sites.

Conclusion: Estimates of searching-associated vector mortality are essential before the effects of changing animal husbandry practices can be predicted. With realistic values of searching-associated vector mortality rates, zooprophylaxis may be ineffective. However, use of animals as bait to attract mosquitoes to insecticide is predicted to be a promising strategy.

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Simulation of an arbovirus epidemic: use of animals to attract mosquitoes to insecticide. Black line: Mf = 0; red line: Mf = 0.1; green line: Mf = 0.2 (ie. a 0, 10, or 20% chance of being killed as a result of feeding on animals respectively). Ms = 0.04 h-1, Pm = 0.72, Aa = 25. Top graph (A): N0 = 96; lower graph (B): N0 = 960. Other parameters are those used for Fig. 6 (Table 3). In Fig. 9A, the black line is the same as the red line in Figs. 6 and 7 for Ms = 0.04 h-1.
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Figure 9: Simulation of an arbovirus epidemic: use of animals to attract mosquitoes to insecticide. Black line: Mf = 0; red line: Mf = 0.1; green line: Mf = 0.2 (ie. a 0, 10, or 20% chance of being killed as a result of feeding on animals respectively). Ms = 0.04 h-1, Pm = 0.72, Aa = 25. Top graph (A): N0 = 96; lower graph (B): N0 = 960. Other parameters are those used for Fig. 6 (Table 3). In Fig. 9A, the black line is the same as the red line in Figs. 6 and 7 for Ms = 0.04 h-1.

Mentions: As for the malaria epidemic model, using animals to attract mosquitoes to an insecticide was predicted to be a highly effective means of slowing the rate at which an epidemic of arbovirus would spread (Fig. 9A). The input parameters chosen for the simulations shown in this figure give an R0 close to 1 with a 20% feeding related vector mortality. As a result, this simulation illustrates the maximum impact that such a treatment would have. Nevertheless, at a 10-fold higher level of transmission, the impact is still highly significant (Fig. 9B) with an initial 54% decrease in the number of human cases, rising to 72% decrease at day 30.


Zooprophylaxis or zoopotentiation: the outcome of introducing animals on vector transmission is highly dependent on the mosquito mortality while searching.

Saul A - Malar. J. (2003)

Simulation of an arbovirus epidemic: use of animals to attract mosquitoes to insecticide. Black line: Mf = 0; red line: Mf = 0.1; green line: Mf = 0.2 (ie. a 0, 10, or 20% chance of being killed as a result of feeding on animals respectively). Ms = 0.04 h-1, Pm = 0.72, Aa = 25. Top graph (A): N0 = 96; lower graph (B): N0 = 960. Other parameters are those used for Fig. 6 (Table 3). In Fig. 9A, the black line is the same as the red line in Figs. 6 and 7 for Ms = 0.04 h-1.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC222927&req=5

Figure 9: Simulation of an arbovirus epidemic: use of animals to attract mosquitoes to insecticide. Black line: Mf = 0; red line: Mf = 0.1; green line: Mf = 0.2 (ie. a 0, 10, or 20% chance of being killed as a result of feeding on animals respectively). Ms = 0.04 h-1, Pm = 0.72, Aa = 25. Top graph (A): N0 = 96; lower graph (B): N0 = 960. Other parameters are those used for Fig. 6 (Table 3). In Fig. 9A, the black line is the same as the red line in Figs. 6 and 7 for Ms = 0.04 h-1.
Mentions: As for the malaria epidemic model, using animals to attract mosquitoes to an insecticide was predicted to be a highly effective means of slowing the rate at which an epidemic of arbovirus would spread (Fig. 9A). The input parameters chosen for the simulations shown in this figure give an R0 close to 1 with a 20% feeding related vector mortality. As a result, this simulation illustrates the maximum impact that such a treatment would have. Nevertheless, at a 10-fold higher level of transmission, the impact is still highly significant (Fig. 9B) with an initial 54% decrease in the number of human cases, rising to 72% decrease at day 30.

Bottom Line: Changing the accessibility of the humans had a much greater effect.Estimates of searching-associated vector mortality are essential before the effects of changing animal husbandry practices can be predicted.With realistic values of searching-associated vector mortality rates, zooprophylaxis may be ineffective.

View Article: PubMed Central - HTML - PubMed

Affiliation: Malaria Vaccine Development Unit, NIAID, NIH, Rockville, MD 20852, USA. ASaul@niaid.nih.gov

ABSTRACT

Background: Zooprophylaxis, the diversion of disease carrying insects from humans to animals, may reduce transmission of diseases such as malaria. However, as the number of animals increases, improved availability of blood meals may increase mosquito survival, thereby countering the impact of diverting feeds.

Methods: Computer simulation was used to examine the effects of animals on the transmission of human diseases by mosquitoes. Three scenarios were modelled: (1) endemic transmission, where the animals cannot be infected, eg. malaria; (2) epidemic transmission, where the animals cannot be infected but humans remain susceptible, e.g. malaria; (3) epidemic disease, where both humans and animals can be infected, but develop sterile immunity, eg. Japanese encephalitis B. For each, the passive impact of animals as well as the use of animals as bait to attract mosquitoes to insecticide was examined. The computer programmes are available from the author. A teaching model accompanies this article.

Results: For endemic and epidemic malaria with significant searching-associated vector mortality, changing animal numbers and accessibility had little impact. Changing the accessibility of the humans had a much greater effect. For diseases with an animal amplification cycle, the most critical factor was the proximity of the animals to the mosquito breeding sites.

Conclusion: Estimates of searching-associated vector mortality are essential before the effects of changing animal husbandry practices can be predicted. With realistic values of searching-associated vector mortality rates, zooprophylaxis may be ineffective. However, use of animals as bait to attract mosquitoes to insecticide is predicted to be a promising strategy.

Show MeSH
Related in: MedlinePlus