Limits...
Implications of Heterogeneous Biting Exposure and Animal Hosts on Trypanosomiasis brucei gambiense Transmission and Control.

Stone CM, Chitnis N - PLoS Comput. Biol. (2015)

Bottom Line: However, the parasite persists in human populations at levels of considerable rarity and as such the existence of animal reservoirs has been posited.We developed a mathematical model allowing for heterogeneous exposure of humans to tsetse, with animal populations that differed in their ability to transmit infections, to investigate the effectiveness of two established techniques, screening and treatment of at-risk populations, and vector control.If they did not serve as reservoirs, sensitivity analyses suggested their attractiveness may instead function as a sink for tsetse bites.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.

ABSTRACT
The gambiense form of sleeping sickness is a neglected tropical disease, which is presumed to be anthroponotic. However, the parasite persists in human populations at levels of considerable rarity and as such the existence of animal reservoirs has been posited. Clarifying the impact of animal host reservoirs on the feasibility of interrupting sleeping sickness transmission through interventions is a matter of urgency. We developed a mathematical model allowing for heterogeneous exposure of humans to tsetse, with animal populations that differed in their ability to transmit infections, to investigate the effectiveness of two established techniques, screening and treatment of at-risk populations, and vector control. Importantly, under both assumptions, an integrated approach of human screening and vector control was supported in high transmission areas. However, increasing the intensity of vector control was more likely to eliminate transmission, while increasing the intensity of human screening reduced the time to elimination. Non-human animal hosts played important, but different roles in HAT transmission, depending on whether or not they contributed as reservoirs. If they did not serve as reservoirs, sensitivity analyses suggested their attractiveness may instead function as a sink for tsetse bites. These outcomes highlight the importance of understanding the ecological and environmental context of sleeping sickness in optimizing integrated interventions, particularly for moderate and low transmission intensity settings.

No MeSH data available.


Related in: MedlinePlus

The proportion of simulations where HAT was eliminated (prevalence < 1 x 10−6) and the mean time to elimination with standard deviation, depending on the percentage of the human population screened per year (expressed as absent (0%), low (20–40%), moderate (40–60%), or high (60–80%) coverage and indicated by the plot titles), with varying levels of vector control (expressed as additional vector mortality, indicated by the symbols in the legend), for a high transmission setting without an animal reservoir (A) and with an animal reservoir (B).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4591123&req=5

pcbi.1004514.g005: The proportion of simulations where HAT was eliminated (prevalence < 1 x 10−6) and the mean time to elimination with standard deviation, depending on the percentage of the human population screened per year (expressed as absent (0%), low (20–40%), moderate (40–60%), or high (60–80%) coverage and indicated by the plot titles), with varying levels of vector control (expressed as additional vector mortality, indicated by the symbols in the legend), for a high transmission setting without an animal reservoir (A) and with an animal reservoir (B).

Mentions: To explore the potential of using an integrated approach of screening and treatment with vector control in more detail in different transmission settings, and depending on whether animals were assumed to to be capable of transmitting infections, we ran sets of 500 simulations whereby both approaches were varied from absent, to low, moderate, or high coverage. For each set we determined the mean time required to reach elimination (i.e., a prevalence < 1 x 10−6) and the proportion of 500 simulations that led to elimination. In the high transmission setting in the absence of animal reservoirs, to achieve the goal of elimination within 20 years and with greater than 80% probability, either vector control at the highest level of efficacy (resulting in a mean time to reach elimination of 19 years), or an integrated approach of screen & treat and vector control was required. A combination of both at our lowest levels of efficacy (20–40% coverage for screening, and a mortality rate between 1–4% for vectors) was sufficient to reach this threshold, and either of the two interventions could be intensified in order to achieve greater probabilities of success or to reduce time to elimination. In general, increasing the intensity of vector control led to greater increases in the probability of eliminating, while increasing the intensity of human screening led to a sharper reduction in the time required to eliminate (Fig 5).


Implications of Heterogeneous Biting Exposure and Animal Hosts on Trypanosomiasis brucei gambiense Transmission and Control.

Stone CM, Chitnis N - PLoS Comput. Biol. (2015)

The proportion of simulations where HAT was eliminated (prevalence < 1 x 10−6) and the mean time to elimination with standard deviation, depending on the percentage of the human population screened per year (expressed as absent (0%), low (20–40%), moderate (40–60%), or high (60–80%) coverage and indicated by the plot titles), with varying levels of vector control (expressed as additional vector mortality, indicated by the symbols in the legend), for a high transmission setting without an animal reservoir (A) and with an animal reservoir (B).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4591123&req=5

pcbi.1004514.g005: The proportion of simulations where HAT was eliminated (prevalence < 1 x 10−6) and the mean time to elimination with standard deviation, depending on the percentage of the human population screened per year (expressed as absent (0%), low (20–40%), moderate (40–60%), or high (60–80%) coverage and indicated by the plot titles), with varying levels of vector control (expressed as additional vector mortality, indicated by the symbols in the legend), for a high transmission setting without an animal reservoir (A) and with an animal reservoir (B).
Mentions: To explore the potential of using an integrated approach of screening and treatment with vector control in more detail in different transmission settings, and depending on whether animals were assumed to to be capable of transmitting infections, we ran sets of 500 simulations whereby both approaches were varied from absent, to low, moderate, or high coverage. For each set we determined the mean time required to reach elimination (i.e., a prevalence < 1 x 10−6) and the proportion of 500 simulations that led to elimination. In the high transmission setting in the absence of animal reservoirs, to achieve the goal of elimination within 20 years and with greater than 80% probability, either vector control at the highest level of efficacy (resulting in a mean time to reach elimination of 19 years), or an integrated approach of screen & treat and vector control was required. A combination of both at our lowest levels of efficacy (20–40% coverage for screening, and a mortality rate between 1–4% for vectors) was sufficient to reach this threshold, and either of the two interventions could be intensified in order to achieve greater probabilities of success or to reduce time to elimination. In general, increasing the intensity of vector control led to greater increases in the probability of eliminating, while increasing the intensity of human screening led to a sharper reduction in the time required to eliminate (Fig 5).

Bottom Line: However, the parasite persists in human populations at levels of considerable rarity and as such the existence of animal reservoirs has been posited.We developed a mathematical model allowing for heterogeneous exposure of humans to tsetse, with animal populations that differed in their ability to transmit infections, to investigate the effectiveness of two established techniques, screening and treatment of at-risk populations, and vector control.If they did not serve as reservoirs, sensitivity analyses suggested their attractiveness may instead function as a sink for tsetse bites.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.

ABSTRACT
The gambiense form of sleeping sickness is a neglected tropical disease, which is presumed to be anthroponotic. However, the parasite persists in human populations at levels of considerable rarity and as such the existence of animal reservoirs has been posited. Clarifying the impact of animal host reservoirs on the feasibility of interrupting sleeping sickness transmission through interventions is a matter of urgency. We developed a mathematical model allowing for heterogeneous exposure of humans to tsetse, with animal populations that differed in their ability to transmit infections, to investigate the effectiveness of two established techniques, screening and treatment of at-risk populations, and vector control. Importantly, under both assumptions, an integrated approach of human screening and vector control was supported in high transmission areas. However, increasing the intensity of vector control was more likely to eliminate transmission, while increasing the intensity of human screening reduced the time to elimination. Non-human animal hosts played important, but different roles in HAT transmission, depending on whether or not they contributed as reservoirs. If they did not serve as reservoirs, sensitivity analyses suggested their attractiveness may instead function as a sink for tsetse bites. These outcomes highlight the importance of understanding the ecological and environmental context of sleeping sickness in optimizing integrated interventions, particularly for moderate and low transmission intensity settings.

No MeSH data available.


Related in: MedlinePlus