MODULE 8 Ecology of Vector-Borne Diseases Notes

Vector-Borne Infectious Diseases

• Involve a causative agent, usually a microorganism, directly causing the disease in the host.

  • Examples of causative agents:

    • Parasites

    • Bacteria

    • Viruses

Vectors and Transmission

• The vector is a living organism, typically an insect, involved in disease transmission.

• Transmission cycle components:

  • An intermediate host organism

  • A reservoir population of organisms (maintaining the agent)

Ecology and Vector-Borne Diseases

• GIS (Geographic Information System) applications model aspects of human-animal-vector interactions within an ecological system.

• Ecological systems are transforming due to:

  • New technologies in production and transportation

  • Human population pressure

  • Climate change

  • Changes in land use

  • Changes in vegetation cover

  • Changes in species and species location

Examples of Vector-Borne Diseases

• West Nile Virus

• Malaria

• Dengue

• Lyme Disease

• Hanta Virus

• Yellow Fever

West Nile Fever: Global Distribution

• Endemic or potentially endemic in 83 countries (according to www.GIDEONonline.com data).

• Annual disease rates per 100,000 population vary by region.

Malaria: Global Distribution

• Control efforts have varying contributions to global deaths (www.GIDEONonline.com data).

• Categories include:

  • High contribution to global deaths

  • Low contribution to global deaths

  • Elimination (pre-elimination and elimination)

  • Malaria-free (prevention of reintroduction and malaria-free)

Global Mortality Estimates from Vector-Borne Diseases

• Mortality rates vary globally, with some regions experiencing much higher death rates per million.

Distribution of Mortality by WHO Region

• Most vector-borne diseases are concentrated in tropical and subtropical regions.

• The burden is greatest in developing countries.

• Mortality estimates for major vector-borne diseases are provided in thousands for each region.

Surveillance and Mapping

• Surveillance methods:

  • Human case surveillance (often relies on human reports).

  • Animal surveillance (limited by spatial biases).

    • Wildlife surveillance (e.g., rabies).

    • Livestock surveillance (e.g., Rift Valley fever).

  • Vector surveillance

Temporal and Spatial Integration of Surveillance Data

• GIS is effective for integrating data temporally and spatially.

• Applications include:

  • Understanding regional variation in vectors and diseases.

  • Modeling vector-borne diseases.

  • Understanding ecological processes in transmission.

  • Identifying endemic areas.

GIS Analysis

• GIS analysis facilitates:

  • Mapping likely distribution of vectors and hosts.

  • Evaluating environmental characteristics of observed cases.

  • Assessing likely impacts of global climate change.

• Provides vital information for public health stakeholders.

Climate Change and Vector-Borne Diseases

• Weather factors influencing vector-borne diseases:

  • Temperature

  • Humidity

  • Surface water

  • Wind speed

  • Precipitation

• Most impactful in tropical and subtropical regions.

Temporal Trajectory of Temperature in Ghana

• A study from 1900-2009 shows temperature trends in ten regions of Ghana (Adu-Prah & Tetteh, Applied Geography, 60:266-273).

Temporal Trajectory of Rainfall in Ghana

• Data from 1900-2009 showing 30-year regional rainfall patterns in Ghana (Applied Geography, 60:266-273).

Regional Cumulative Malaria Prevalence in Ghana (1995-2006)

• Visualization of malaria prevalence across different regions, with prevalence rates per 100,000 population.

Regional Spatiotemporal Malaria Prevalence in Ghana (1995-2006)

• Maps illustrating malaria prevalence variations across regions of Ghana from 1995 to 2006 (Applied Geography, 60:266-273).