Guest Essay by Kip Hansen
You would think that science journalists have been carefully trained to research the topics they write about, especially in high-profile media outlets such as the New York Times. It is a shame that careful back-grounding has become a thing of the past even in these prestigious newsrooms.
“A new study offers a glimpse of the future by looking to the past. Mosquitoes that transmit malaria in sub-Saharan Africa have moved to higher elevations by about 6.5 meters (roughly 21 feet) per year and away from the Equator by 4.7 kilometers (about three miles) per year over the past century, according to the study.”
“That pace is consistent with climate change and may explain why malaria’s range has expanded over the past few decades, the authors said. The results have serious implications for countries that are unprepared to cope with the disease.”
The article was prompted by a recent study (yes, “There is a Study!”) that appeared in Biology Letters with the title: “Rapid range shifts in African Anopheles mosquitoes over the last century” by Carlson et al. (2023).
This study claims to have found “Mosquitoes that transmit malaria in sub-Saharan Africa have moved to higher elevations by about 6.5 meters (roughly 21 feet) per year and away from the Equator by 4.7 kilometers (about three miles) per year over the past century, according to the study.”
I won’t quibble with their actual findings….it is a result of rather obtuse calculation across heterogenous data sets. But we catch the lead author, Colin Carlson, giving this quote to the Times:
“If this were random, and if it were unrelated to climate, it wouldn’t look as cleanly climate-linked.”
Our Times journalist, Mandavilli, said “A new study offers a glimpse of the future by looking to the past.”
Unfortunately, the neither the authors or Mandavilli seem to have looked far enough or closely enough into the past to realize that their conclusions and worries are not supported by real world historical facts. Other epidemiologists have taken notice, as reported in the “Discussion” section of the paper:
“Others have disputed these conclusions, suggesting that they are irreconcilable with long-term progress towards malaria elimination, that trends in the region are better explained by lapsed control programmes and growing drug resistance, and that climate change is inconsistent with long-term trends at the continental scale.”
And these others have quite rightly disputed the conclusions, which totally fail to take into account several overriding facts:
1) The worry isn’t that Africans might be bitten by mosquitoes – they will, always and almost everywhere in Africa (except the Sahara and other northern deserts). It is about the locations of African malaria mosquito vectors (Anopheles spp.).
2) But what is the real historical data about where in Africa malaria is a threat — where malaria is endemic?
That map is Malaria Transmission – not just where Anopheles mosquitoes live. That shows the history malaria transmission in Africa since 1900.
And closer to today?
This map shows where the species that is the reservoir of malaria has been actually found to have malaria in its blood — meaning the individual is sick with malaria or is a carrier of malaria.
What species is that?
“Reservoir: Humans are the only important reservoir of human malaria. Mode of Transmission: Malaria is transmitted by the bite of an infective female Anopheles mosquito. Transfusion of blood from infected persons and use of contaminated needles and syringes are other potential modes of transmission. Apr 2, 2014 MALARIA FACT SHEET State of Georgia” (.pdf)
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Reservoir and Vector in Malaria
Humans are the Reservoir of malaria – The Agent of malaria is an amoeba of the Plasmodium group (there are several) – The Vector of malaria is an Anopheles mosquito – The Host of malaria is, again, a Human, who becomes part of the Reservoir.
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3) Wasn’t malaria spread around the world by Anopheles mosquitoes?
“MALARIA’S GLOBAL SAGA”
“Malaria occupies a unique place in the annals of history. Over millennia, its victims have included Neolithic dwellers, early Chinese and Greeks, princes and paupers. In the 20th century alone, malaria claimed between 150 million and 300 million lives, accounting for 2 to 5 percent of all deaths (Carter and Mendis, 2002). Although its chief sufferers today are the poor of sub-Saharan Africa, Asia, the Amazon basin, and other tropical regions, 40 percent of the world’s population still lives in areas where malaria is transmitted.”
“Malaria’s probable arrival in Rome in the first century AD was a turning point in European history. From the African rain forest, the disease most likely traveled down the Nile to the Mediterranean, then spread east to the Fertile Crescent, and north to Greece. Greek traders and colonists brought it to Italy. From there, Roman soldiers and merchants would ultimately carry it as far north as England and Denmark (Karlen, 1995).”
“For the next 2,000 years, wherever Europe harbored crowded settlements and standing water, malaria flourished, rendering people seasonally ill, and chronically weak and apathetic. “
From : “Saving Lives, Buying Time: Economics of Malaria Drugs in an Age of Resistance”
Malaria, historically, has been spread by human movements – humans who harbor the malarial parasites and humans who inadvertently spread the mosquitos that transmit malaria to new locales.
4) But isn’t malaria eliminated by eliminating Anopheles mosquitoes?
No, not exactly. Maybe not at all. Here’s a map of malaria deaths in the United States in 1870:
Malaria deaths as far north as Michigan, above Chicago, and even some in Vermont.
When was it eliminated?
With this blow-up, we see that malaria wasn’t eliminated in the United States in some areas until as late as 1965. How do we eliminate malaria? Kill all the mosquitoes?
The Anopheles quadrimaculatus mosquito is found today in a wide range of east of the Rocky Mountains, but malaria has been totally eliminated.
How? By quarantining humans who contract malaria until their blood is free of the parasites. Humans are the reservoir of malaria, without malarial humans, the mosquitoes have nothing to spread.
Note: Occassionally, travelers return to the United States having contracted malaria in the Caribbean or Africa or other malarial areas. Once they are identified, they are treated in a hospital with anti-malarials. Malaria is a “nationally notifiable disease” which means doctors and hospitals are required/encouraged to report cases to the CDC.
5) In areas that are prone to outbreaks of mosquito transmitted diseases, and there are several, tracking mosquito problem areas and spraying for mosquitoes is an important public health effort. Outbreaks are often traced back to ”lapsed control programmes” — failure to maintain mosquito spraying programs by states, counties, and municipalities. Activists and lack of funds are the two most common reasons that spraying is discontinued.
1. Humans, not mosquitoes, are the reservoir of malaria. Humans sick with malaria spread malaria. Historically, human trade, exploration and military movements are responsible for spreading malaria worldwide. Mosquitoes are just the vector which moves malaria from one sick human to another (sometimes many).
2. Malaria is eliminated by treating humans and preventing malarial humans from being bitten by mosquitoes, who would then spread the disease.
3. Claims that small expansions or changes in habitat size or location of various Anopheles mosquito species are a “new threat” to African populations that might somehow, after centuries, be “unprepared to cope with the disease” are unfounded and alarmist.
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This is not the first time I have written about malaria and mosquito vectored diseases here.
I spent a day and a half on this essay — Apoorva Mandavilli at the Times writes one story every couple of weeks. Maybe she has another job that I don’t know about. But maybe she could have researched the history of malaria and determined that the study did not uncover yet another threat to humanity.
Mandavilli does at least include this caveat paragraph: “Some mosquito movement may also be because of changes in land use, the availability of food or a side effect of people migrating to higher elevations because of climate change, experts said. Still, disease-bearing mosquitoes are of serious concern in areas where people and institutions are unprepared.” Or rapidly increasing African populations that just need somewhere to farm and live.
Thanks for reading.
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via Watts Up With That?
February 19, 2023 at 12:15AM