Lesson 9 of 9 / Climate change, food and disease vectors
Explain how disease risk can move beyond the tropics
What must connect warming to actual transmission?
In this lesson: Explain how warming can change malaria and dengue transmission ranges while recognising other required conditions.
About 6 min
The key ideaWarming can make some cooler places or seasons more suitable for vectors and pathogen development. Transmission still requires the right mosquito, the pathogen and contact with susceptible hosts.
Explore the idea
Suitability is only one transmission link
Adding suitable warmth does not create a pathogen. Introducing a pathogen does not guarantee that a vector can survive and transmit it.
Concept model, not a current disease-risk forecast. Dengue: Aedes and a virus. Malaria: Anopheles and Plasmodium parasites.
Explanation
Dengue is caused by a virus and is transmitted mainly by infected female Aedes aegypti mosquitoes. Malaria is caused by Plasmodium parasites and is transmitted by infected female Anopheles mosquitoes. A vector carries the pathogen between hosts; the mosquito and disease agent are not the same organism.
Warmer conditions can make some formerly cool areas, including places beyond the tropics or at higher elevation, more suitable for mosquito survival and reproduction. A longer suitable season can increase the time available for transmission. Within suitable limits, warming can also speed pathogen development inside the mosquito, allowing it to become infectious sooner.
These changes can increase the opportunity for local transmission if competent vectors and the pathogen are introduced or already present. Travel and movement of goods can help introduce hosts, vectors or pathogens; breeding water, humidity and human-vector contact affect whether transmission is sustained.
The response is not a simple expansion everywhere. Excessive heat or drought can reduce mosquito survival, and surveillance, habitat management and vector control can reduce transmission even under a suitable climate. Warming changes part of the risk system rather than guaranteeing disease in every warmer location.
To evaluate evidence, separate climate suitability, presence of vectors and confirmed local transmission. A rise in reported cases may also reflect travel, reporting changes or other conditions. Explain a plausible mechanism, then identify what additional observations would test it.
Step by step
- 1
Identify vector and pathogen correctly
Aedes with dengue virus; Anopheles with malaria parasites.
- 2
Connect warming to suitability
Consider survival, development, seasonal duration and pathogen development.
- 3
Check the rest of transmission
Pathogen introduction, breeding sites, hosts, contact and control all matter.
Worked example
A suitable vector, but no local cases
A formerly cool region now supports a mosquito species capable of carrying dengue, but no locally acquired dengue has been detected. Is that evidence that temperature has no relevance?
One way to explain it
No. Climate suitability can change before all conditions for local transmission are met. The virus must be present and passed through infected vectors to susceptible hosts; surveillance and control also affect the observed outcome. Vector presence alone is not proof of an outbreak.
Why this answer works
- Distinguish potential risk from observed transmission.
- Name a missing biological link rather than assuming temperature creates a pathogen.
Is this true? "Aedes causes malaria and Anopheles creates the dengue virus when it gets warm."
Dengue virus is mainly transmitted by Aedes, while malaria parasites are transmitted by Anopheles. Warming can affect their transmission systems but does not create either pathogen.