The podcast of the University of Colorado Consortium for Climate Change and Health
Episode 8: Climate Change and Vector-Borne Disease
Attention Humans co-hosts interview Dr. Rosemary Rochford, who explains the links between mosquito-borne diseases and the changing climate.
Biography:
Dr. Rochford earned her PhD in Biochemistry at the University of California Irvine, and is currently a professor in the Department of Immunology and Microbiology at the University of Colorado School of Medicine. Her research interests include climate-sensitive vector-borne diseases, such as malaria. Currently, she is the director of the University of Consortium for Climate Change and Health and one of our mentors for the Attention Humans podcast.
Episode Highlights:
To start, let’s define a few terms we use in the episode:
Vector
In the context of infectious diseases, a “vector” is the vehicle that carries and transmits a disease-causing agent. As a few examples: fleas were vectors for the bubonic plague, bats are the (primary) vectors for the rabies virus, and mosquitos are the vectors for malaria. Above is a CDC picture of an Anopheles mosquito, which can carry and transmit malaria.
Public Health Infrastructure
Broadly speaking, “public health infrastructure” refers to the systems that prevent disease and support the health and wellbeing of a community. General examples include water sanitation facilities, outbreak investigators, and air quality monitoring. In the context of vector-borne diseases, public health infrastructure could refer to disease and vector monitoring, source control (i.e. modifying the environment so that mosquitos cannot breed), and the availability of mosquito nets to prevent disease transmission. In the above image from the CDC, a worker inspects a mosquito net.
Mitigation
“Mitigation” refers to efforts to reduce greenhouse gas emissions and thereby slow the progression of global climate change. Examples of mitigation strategies include renewable energies (wind and solar), zero-emissions vehicles (i.e. electric cars), and carbon capture and storage. Above, an image of solar panels at the EPA regional office in Denver, CO.
Adaptation
“Adaptation” refers to strategies that protect us from climate change-related threats, thereby enabling us to continue living amidst the changing climate. Examples of adaptation strategies include public cooling centers, green roofs (to reduce urban heat island effect), and storm-resistant buildings. Above, a picture of a grass roof (from the EPA website), which absorbs less heat than traditional building materials.
Over the course of the interview, Dr. Rochford mentions several different mosquitos and the diseases they carry. We overview them in broad strokes below–take a look:
Anopheles Mosquitos
Anopheles is the vector for the Plasmodium parasite, which causes malaria.
Aedes Mosquitos
Geographic Distribution
Aedes is the vector for several viruses, including Dengue (below), Zika, and Chikungunya.
Culex Mosquitos
Culex is the vector for West Nile Virus.
While we all know mosquitos to be a nuisance, the diseases they carry and transmit to humans can make us very sick. Dr. Rochford summarizes the symptoms of some of these illnesses in the podcast, and you can explore them further below:
Malaria
Approximate time from mosquito bite to development of symptoms: ≥ 2 weeks
Common, non-specific symptoms: fever, headache, chills, body-aches, nausea and vomiting.
Distinct symptoms: waxing and waning fever (e.g. “diurnal fever” in Plasmodium vivax or ovale infection), anemia (low red blood cell count)
Treatment: antimalarial (AKA anti-parasitic) medication (e.g. artemisinin, mefloquine, etc.)
Above, an image from the CDC of a mother suffering from malaria.
Dengue Fever
Approximate time from mosquito bite to development of symptoms: 4-7 days
Common, non-specific symptoms: fever, headache, body-aches, joint pain, eye pain, rash, nausea and vomiting.
Distinct symptoms: low white blood cell count, bleeding problems and shock (formerly called Dengue hemorrhagic fever and Dengue shock syndrome, which can occur if infected by two different types of the Dengue virus)
Treatment: treat symptoms, no anti-viral medication available
Above, pictures from UpToDate of two children with rash caused by the Dengue virus.
Zika Fever
Approximate time from mosquito bite to development of symptoms: 3-14 days
Common, non-specific symptoms: fever, headache, body-aches, joint pain, eye pain, rash, and conjunctivitis
Distinct symptoms: congenital Zika syndrome (microcephaly, pictured on right)
Treatment: treat symptoms, no anti-viral medication available
Above, photographs and radiologic imaging of babies born to mothers infected with Zika virus during pregnancy. Images and a detailed discussion of the birth defects that can result from fetal exposure to Zika virus are from an article by Moore et al. (2018) in JAMA Pediatrics.
Chikungunya
Approximate time from mosquito bite to development of symptoms: 3-7 days
Common, non-specific symptoms: fever, headache, body-aches, joint pain, rash, and conjunctivitis
Distinct symptoms: severe joint pain and swelling
Treatment: treat symptoms, no anti-viral medication available
Above, an image from UpToDate showing a severe systemic rash resulting from infection with the Chikungunya virus.
West Nile Fever
Approximate time from mosquito bite to development of symptoms: 2-6 days
Common, non-specific symptoms: fever, headache, body-aches, rash, nausea and vomiting
Distinct symptoms: severe and potentially fatal neurologic symptoms (“West Nile Encephalitis”)
Treatment: treat symptoms, limited medical treatment options available
Above, brain scans of a patient with severe, progressive West Nile virus infection involving the brain, from an article by Gea-Banacloche et al. (2004) in the Annals of Internal Medicine.
Why is it important to learn about these mosquito-borne diseases? As Dr. Rochford explains, many vector-borne diseases are also sensitive to changes in the climate. She uses malaria–a climate-sensitive disease–as an example of how the distribution and burden of vector-borne diseases can shift with global climate change. How exactly does this happen? The mosquito and Plasmodium parasite lifecycle (shown in the CDC figure below) can be influenced by the climate at several different points. To use Dr. Rochford’s words, “It’s complicated”…
It’s complicated indeed. In the episode, Dr. Rochford explains that we can focus our attention on two climatic factors–temperature and precipitation–and think about how these can influence the mosquito and parasite lifecycle. The main points are summarized below:
In words, increased temperatures (to a point) can increase the number of mosquitos as well as the replication rates of the malaria-causing parasites they carry. Changes in precipitation can potentially make mosquito populations more difficult to control (by providing them more habitats), and can disrupt the infrastructure many communities have in place to protect individuals from exposure to malaria-carrying mosquitos. That said, it is worth reiterating that the relationship between precipitation and malaria is far from straightforward.
Looking to the future, it is projected that the global distribution of malaria will change with the changing climate. Some regions may no longer be suitable for the Anopheles vector, whereas other communities–previously naive to malaria–may have a new disease vector on their hands. This is illustrated in the map below, produced by Hugo Alhenius of UNEP/GRID-Arendel.
To close out this episode, we ask Dr. Rochford (who is also the director of the CU Consortium for Climate Change and Health) about her vision for the future of the Consortium. Our conversation distilled down to a few words: we want more students at the table.
If you are interested in learning more or getting involved, please leave a comment below, or email us at attentionhumanspodcast@gmail.com, jacob.fox@ucdenver.edu, or rosemary.rochford@ucdenver.edu.
Shownotes
background readings and resources for the interested listener:
