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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 a malaria 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, Pov = 0.72, N0 = 960, Aa = 25. Other parameters are those used for Fig. 3 (Table 3). The black line is the same as the red line in Fig. 3 for Ms = 0.04 h-1.
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Figure 5: Simulation of a malaria 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, Pov = 0.72, N0 = 960, Aa = 25. Other parameters are those used for Fig. 3 (Table 3). The black line is the same as the red line in Fig. 3 for Ms = 0.04 h-1.

Mentions: As for the models of endemic malaria, the epidemic model was also used to assess the impact of using animals to attract mosquitoes to an insecticide. The model was run with a range of probabilities that mosquitoes attracted to animals would be killed and again, since animals are not hosts for malaria, identical results are obtained if the mosquitoes die before or after feeding on animals. The model was run with the same parameters used for Fig. 3. Although the absolute rates at which the outbreak occurred were different, similar relative impacts were seen on the evolution of the malaria outbreak at all values of Ms tested. Only the results obtained for an Ms of 0.04 h-1 are shown (Fig. 5). In all cases, a major impact on the spread of malaria occurred when even a small proportion of the mosquitoes attracted to animals were killed.


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 a malaria 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, Pov = 0.72, N0 = 960, Aa = 25. Other parameters are those used for Fig. 3 (Table 3). The black line is the same as the red line in Fig. 3 for Ms = 0.04 h-1.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 5: Simulation of a malaria 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, Pov = 0.72, N0 = 960, Aa = 25. Other parameters are those used for Fig. 3 (Table 3). The black line is the same as the red line in Fig. 3 for Ms = 0.04 h-1.
Mentions: As for the models of endemic malaria, the epidemic model was also used to assess the impact of using animals to attract mosquitoes to an insecticide. The model was run with a range of probabilities that mosquitoes attracted to animals would be killed and again, since animals are not hosts for malaria, identical results are obtained if the mosquitoes die before or after feeding on animals. The model was run with the same parameters used for Fig. 3. Although the absolute rates at which the outbreak occurred were different, similar relative impacts were seen on the evolution of the malaria outbreak at all values of Ms tested. Only the results obtained for an Ms of 0.04 h-1 are shown (Fig. 5). In all cases, a major impact on the spread of malaria occurred when even a small proportion of the mosquitoes attracted to animals were killed.

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