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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 endemic malaria with varying numbers of animals used as bait to attract mosquitoes to insecticide. Black line: Mf = 0; red line: Mf = 0.2; green line: Mf = 0.4; blue line: Mf = 0.6 (ie. a 0, 20, 40 or 60% chance of being killed as a result of feeding on animals respectively). Ms = 0.04 h-1, Pov = 0.72, N0 = 960. Other parameters are those used for Fig. 1 (Table 2). The black line (Mf = 0) is the same as the green line in Fig. 1.
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Figure 2: Simulation of endemic malaria with varying numbers of animals used as bait to attract mosquitoes to insecticide. Black line: Mf = 0; red line: Mf = 0.2; green line: Mf = 0.4; blue line: Mf = 0.6 (ie. a 0, 20, 40 or 60% chance of being killed as a result of feeding on animals respectively). Ms = 0.04 h-1, Pov = 0.72, N0 = 960. Other parameters are those used for Fig. 1 (Table 2). The black line (Mf = 0) is the same as the green line in Fig. 1.

Mentions: To investigate the use of animals to attract vectors to insecticide, the model was re-run using the combinations on Fig. 1 using Ms of 0.04 h-1, but considering the animals as bait with varying probabilities of killing associated with feeding on these animals (Yb varied from 0 to 100, Ab 0.004 h-1, Yh 100, Ah 0.001 h-1, N0 960, Pov 0.72, Mf of 0, 0.2, 0.4 and 0.6). In this simulation, the animals are not a host for malaria, and the outcome of the numerical simulation is identical if the mosquitoes die before or after feeding on the bait animals (Fig. 2).


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 endemic malaria with varying numbers of animals used as bait to attract mosquitoes to insecticide. Black line: Mf = 0; red line: Mf = 0.2; green line: Mf = 0.4; blue line: Mf = 0.6 (ie. a 0, 20, 40 or 60% chance of being killed as a result of feeding on animals respectively). Ms = 0.04 h-1, Pov = 0.72, N0 = 960. Other parameters are those used for Fig. 1 (Table 2). The black line (Mf = 0) is the same as the green line in Fig. 1.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 2: Simulation of endemic malaria with varying numbers of animals used as bait to attract mosquitoes to insecticide. Black line: Mf = 0; red line: Mf = 0.2; green line: Mf = 0.4; blue line: Mf = 0.6 (ie. a 0, 20, 40 or 60% chance of being killed as a result of feeding on animals respectively). Ms = 0.04 h-1, Pov = 0.72, N0 = 960. Other parameters are those used for Fig. 1 (Table 2). The black line (Mf = 0) is the same as the green line in Fig. 1.
Mentions: To investigate the use of animals to attract vectors to insecticide, the model was re-run using the combinations on Fig. 1 using Ms of 0.04 h-1, but considering the animals as bait with varying probabilities of killing associated with feeding on these animals (Yb varied from 0 to 100, Ab 0.004 h-1, Yh 100, Ah 0.001 h-1, N0 960, Pov 0.72, Mf of 0, 0.2, 0.4 and 0.6). In this simulation, the animals are not a host for malaria, and the outcome of the numerical simulation is identical if the mosquitoes die before or after feeding on the bait animals (Fig. 2).

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