Disease Vectors

What is a Disease Vector? An organism that transmits an infectious agent into another organism Begin by asking class if they know what a disease vector is. Welcome several student answers, if possible, then provide definition. Then ask if students know how vectors transmit diseases. Welcome several student answers, if possible, and then show disease vector cycle.

What are some disease vectors? Fleas Cats Mosquitoes Ticks Bats What are some vector-borne diseases? Ask students to think of disease vectors and vector-borne diseases. This will ideally generate some classroom discussion. Have students debate whether certain organisms or diseases are vectors or vector-borne diseases. When discussion lulls, show the above lists of common vectors and diseases, and address any other vectors/diseases that students mentioned. African Sleeping Sickness Malaria West Nile Virus Lyme Disease

Disease Vectors and Ecology Like other organisms, disease vector populations are dependent on ecosystem conditions Changes in these conditions affect vector populations and human disease rates Dr. Brian Allan researches how ecological changes impact disease vector populations and human health

Dr. Brian Allan: Forest Fragmentation Forest fragmentation occurs when wooded areas are cleared for development of farm fields, homes, or businesses, causing smaller plots of trees Dr. Allan found that the smaller the forest fragment, the greater the number of deer ticks, and the greater the human risk for lyme disease Why might this be? Entertain several theories on this correlation. Ask guiding questions to stimulate discussion. (How would forest fragmentation affect the kind of animals that live there? What do ticks need to live?) Ask other students to evaluate the plausibility of these theories.

Forest fragmentation increases the number of small mammals, such as mice, because fewer large predators can live in small forest fragments. Deer ticks host primarily on these small mammals, so their numbers also increase. Reveal Dr. Allan’s findings. Discuss whether or not student theories could also explain the increase in deer ticks.

Dr. Brian Allan: Bird Diversity Bird diversity is the number of different species of birds in an area; human pressures are causing average bird diversity to decrease Dr. Allan found that areas with low bird diversity have higher rates of mosquitoes infected with West Nile Virus Why might this be? Entertain several theories on this correlation. Ask guiding questions if necessary. (Do you think mosquitoes like to bite certain species of animals more than others? Why?) Have students discuss the plausibility of these theories.

With fewer species of birds, mosquitoes become better adapted to feed on these species. This increases mosquito-bird interaction, facilitating the spread of West Nile Virus. This might be a little difficult for students to grasp, as it is kind of counterintuitive. Explain that the blood if different bird species might have different antibodies or other factors that could be harmful to mosquitoes. With fewer species around, mosquitoes become really good at feeding on these bird species, and don’t get killed off by feeding on the “bad” bird species.

Dr. Brian Allan: Precipitation Rates Climate change has altered the average precipitation rates; in some areas, this has led to drought, and in other areas it has led to flooding Dr. Allan found that mosquito populations and rates of West Nile Virus are greater in years after heavy rainfall Why might this be? Entertain several student theories on the correlation. Ask guiding questions if necessary. (Why might mosquitoes benefit from more rain? Do you think it is the water itself, or something else caused by the rain?) Ask students to critique other student theories.

Mosquitoes depend on pools of water to lay their eggs Mosquitoes depend on pools of water to lay their eggs. In years of excess rain, more pools are available for mosquitoes to use. This increases mosquito populations and subsequently increases rates of human cases of West Nile Virus. Examine the credibility of other student theories. After completing this discussion, the project will be introduced (handout). Encourage students by stating that if they could think critically about these examples, they will be well prepared to explore their disease.