Guest Essay by Kip Hansen – 13 May 2025 – 1500 words

One of the ubiquitous Climate Crisis narratives is that the slight warming of some climate regions is driving the spread of mosquito borne diseases.    This can easily be shown to be incorrect yet the peer-reviewed literature repeats (endlessly) that mosquito-borne diseases will spread, or have been spread, by climate change. 

Malaria, the most famous of vector-borne diseases, for which the female Anopheles mosquito is the vector while humans are the reservoir, has been reappearing in the United States and Europe.  Climate Change or Global Warming has been blamed [and here and, from the WHO, here].  But history shows that both the United States and Europe were hotbeds of malaria in the past two centuries, even during the Little Ice Age,  when temperatures were lower.

[Curious Note:  The Climate Crisis wiki gatekeepers post false information about the LIA in the caption of the Hockey Stick graph.  The caption says “Global average temperatures show that the Little Ice Age was not a distinct planet-wide period but a regional phenomenon…”  But the reference given for that, from Ed Hawkins (long-standing climate crisis scientist and propagandist), states clearly “The often quoted Medieval Warm Period and Little Ice Age are real phenomena, but small compared to the recent changes.”]

Here we can see, from Hong et al., that malaria was very widely spread in the United States in the 1850s.

The incidence of malaria in Europe was equally widespread, even up into World War I:  “In 1917, 70,000 cases of malaria were reported in the British forces alone.  After the war, malaria spreader-emerged among the civil population in malaria free areas like northern Germany, eastern England and Italy due to the return of soldiers to their homeland and to refugee movements.”  [ source:  NIH here ]. 

“Malaria was eradicated from Europe in the 1970s  through a combination of insecticide spraying, drug therapy and environmental engineering. Since then, it has been mostly imported into the continent by international travelers and immigrants from endemic regions.” [source]

In fact, “Although largely a tropical disease today, only a century ago the pathogen’s [malaria] range covered half the world’s land surface, including parts of the northern USA, southern Canada, Scandinavia and Siberia,” said lead author Megan Michel, a doctoral researcher at the Max Planck-Harvard Research Center…”.  [quote source, paper here] And a “century ago” is the cool time period against which we measure today’s so-called  “global warming”. 

There is an obvious knowledge disconnect here:  In the cooler past, malaria was found nearly everywhere except in the frozen steppes and high altitudes.  Now it is mostly confined to the tropics and sub-tropics.

Why is this? 

The mosquitoes that spread malaria from one malarial human to a well human are ubiquitous in nearly every area of the world.  Mosquito populations are suppressed in modern, wealthy countries through widespread spraying of insecticides and other vector control methods such as swamp draining and transmission of malaria prevented by the quarantine of people ill with malaria in hospitals where mosquitoes cannot bite them.  When vector control, mosquito spraying,  is not done, or curtailed as many cities in the United States have learned, mosquito populations boom and these diseases can reappear as humans traveling in other countries return carrying the disease.  [source]

Now, let see what the situation is with another mosquito-borne disease:

Dog  Heartworm

Your ever-present climate propaganda news outlet, Inside Climate News, says:  “Climate Change Is Helping Heartworm Spread to Pets in the Mountain West”.  Using the normative “narrative journalism” style, ICN goes on to say:

“Twenty years ago, when veterinarian Colleen Duncan arrived in Fort Collins, Colorado, there were no signs of heartworm in the region’s dogs and cats.

“We didn’t test for it,” said Duncan, a professor of veterinary medicine at Colorado State University. “We didn’t put our animals on prevention. We now will do it.”

“Colorado’s not alone in this shift. Across the West, veterinarians are seeing an increase in the mosquito-borne disease that can cause symptoms like coughing and decreased appetite in dogs and cats, and even lead to death in advanced cases.” 

“Infected pets can bring the disease with them when they move to new regions, where a lack of preventative treatment can contribute to an uptick in heartworm infections.”

So far, so good, I guess.  We will take Colleen Duncan at her word. 

But ICN’s journalist Tina Deines then shifts to:

“Vector-borne disease is the easiest, the least-disputed discussion of climate-associated diseases,” said Duncan, who studies the connection between climate change and animal health. 

“Climate change moves vectors into areas, geographic locations that they weren’t before,” she explained. “It allows them to survive longer periods of time. Typically, they show up earlier in the spring and they last later into the fall. Or even really winter.”

“We keep dogs on heartworm preventative year-round now,” she said.”

Now we find that Colleen Duncan is not just a vet, she is an academic vet “who studies the connection between climate change and animal health” about which “She is passionate”.

It is informative to note that the population of Fort Collins,  Colorado has doubled since 1990, from 89 thousand then to over 170 thousand today.

What’s the real deal here then?

Most of us, even though many of us are dog owners [but not passionate climate change vets], are not familiar with the basics of Dog Heartworm Disease.  The following quotes are from the American Heartworm Society:

“Heartworm disease is a serious and potentially fatal disease in pets in the United States and many other parts of the world. It is caused by foot-long worms (heartworms) that live in the heart, lungs and associated blood vessels of affected pets, causing severe lung disease, heart failure and damage to other organs in the body.”

“The dog is a natural host for heartworms, which means that heartworms that live inside the dog,  mature into adults, mate and produce offspring.”

“When a mosquito bites and takes a blood meal from an infected animal, it picks up these baby worms, which develop and mature into “infective stage” larvae over a period of 10 to 14 days. Then, when the infected mosquito bites another dog, cat, or susceptible wild animal, the infective larvae are deposited onto the surface of the animal’s skin and enter the new host through the mosquito’s bite wound.”

For Dog Heartworm, the mosquito is the vector and dogs are the host or reservoir.  If there were no dogs with existing heartworm infections, there would be no heartworm for the mosquitoes to spread to other dogs. 

This is similar to human malaria, which requires malarial humans for mosquitoes to bite in order to spread the disease.  When all the malarial humans are quarantined in mosquito-free hospitals, the chain is broken.   If no local dogs (rarely some cats, some ferrets, maybe) had heartworm infections, there would be no heartworm microfilaria for the mosquitoes to ingest, incubate, and pass on to other dogs.

Which specific mosquitoes spread Dog Heartworm?

Many species of mosquitoes are suspected of being vectors for dog heartworm, including Aedes, Anopheles, and Mansonia and Culex.These mosquito species are endemic to most/many areas of the United States (species dependent).   

All three of the species below are main vectors for serious human and animal diseases.

 

Mosquitoes are moved from area to area and into new areas by humans – not climate change, not global warming.  [ source:  The Push: Human Migration and Mosquito-Borne Disease ].  Mosquitoes hitchhike in luggage, air and sea freight, in and on over-the-road long distance trucks,  and on the decks of ships and boats. 

Urban mosquitoes, like  Aedes aegypti and Aedes Albopictus prefer urban environments, in which they find it easy to thrive:  “Aedes aegypti favors artificial containers found in residential areas like flowerpots, buckets, tarps, bird baths, and potholes as breeding sites. Aedes Albopictus can breed in a variety of natural and artificial containers such as tree holes, rock pools, tires, stormwater drains, and concrete slabs.”  [ source ]. 

Urbanization itself creates the preferred environment of vector mosquitoes that spread disease: “The main explanatory variables used to associate urbanisation with epidemiological/entomological outcomes were the following: human population density, urban growth, artificial geographical space, urban construction, and urban density.”  [source]

Which mosquitoes are urban and semi-urban species?

Aedes, Culex and Anopheles are usually considered prime urban and semi-urban species – which means that thrive in human built environments: the denser the humans, the better for the mosquitoes.   These are the same species that are prime suspects in Dog Heartworm transmission.

Bottom Lines:

0.  Malaria, dengue, dog heartworm and many other vector borne diseases all require three things for transmission:  a) a host with the disease causing organism – germ, virus, or parasite;  b) the presence of the vector such as specific species of mosquitoes or ticks; c) vectors require access to both disease carriers and new disease victims.  Absence of any of these stops the chain of infection.  

1.  Humans are responsible for the range expansion of mosquito species, providing urban and semi-urban environments with their warm, water-rich spaces and through physically transporting mosquitoes from area to area, country to country.

2.  Humans are responsible for the re-emergence of mosquito-as-vector diseases in developed countries, through human travelers carrying the disease returning from the developing world and the shipments goods from malaria areas. 

3.  Dog Heartworm has been spread by humans moving their heartworm infected animals to areas previously heartworm free and through introducing or re-introducing mosquito species that act as vectors and/or increasing populations of those mosquito vectors by the common features of urbanization. 

4.  The increase of dog heartworm found in Fort Collins, Colorado has been caused by import of dogs with heartworm (moving there with the human families), human movements (people and goods) transporting more mosquito species to the area and a doubling of human population with its increased urbanization, creating more of ideal urban and semi-urban environment for the mosquito vectors of heartworm.   

4.  Climate Change or Global Warming has no (or vanishingly minimal contribution) to the range changes of mosquito species and/or the spread of mosquito-vectored human and animal diseases.

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Author’s Comment:

Dog Heartworm is a backdoor into the misinformation spread about mosquito and other insect vectored diseases.  Warming, mostly at night,  has barely any effect on the ranges of mosquitoes and ticks.  Past ranges,  when compared to present ranges,  prove this.

Weather can and does have effects on mosquito populations such as when areas that are usually dry are subject to flooding.  Eggs that have been lying dormant hatch and in days go through larval stages and become (ravenous) mosquitoes.   When this happens in malaria, zika and dengue areas, the mosquitoes bite the local human disease carriers and spread the diseases.  And, yes, Weather is not Climate. 

Despite the apparent ease of debunking this climate crisis talking point,  there are literally hundreds of papers claiming to “prove” the false point or “predict” that “if not now, then in the future”.

Thanks for reading.

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