Heat in on

I have done and share some research about the potential effects of climate change in vector-borne illnesses such as malaria, a biological agent, and some possible ways to overcome this problem, but what about another kind of threat: heat.

Heat stress is mentioned in the Atlas of Health and Climate as a danger for human life. It “occurs when the body’s means of controlling its internal temperature starts to fail”. 

The body controls the internal temperature by sweating; blood transports the heat from the inside to the surface (skin) and by evaporation (sweating) it is liberated; that is why in hot days it feels hotter and more uncomfortable in places with high humidity.

As heat stress is more dangerous in urban area (Argüeso) than in rural ones and as it is affected by climate change I have decided to explicitly mention the symptoms indicated in HSE (UK):

·         an inability to concentrate

·        - muscle cramps

·       -  heat rash

·       -  severe thirst - a late symptom of heat stress

·       -  fainting

·      -  heat exhaustion - fatigue, giddiness, nausea, headache, moist skin

·       -  heat stroke - hot dry skin, confusion, convulsions and eventual loss of consciousness. This is the most severe disorder and can result in death if not detected at an early stage

A study made in China by Ma, shows that heat waves have significantly (5%) increased mortality. The effects depend on variables as age, gender, population density, region inside the country; meaning the mitigation/adaptation measures should be developed at local level.

Note 1: This conclusion could mean that it would be necessary to make a study city by city (if not neighbour by neighbour) to define the correct adaptation measures to heat, including among other topics: hospital and schools infrastructure, public transportation, working hours and so on. This would mean funds. I presume the lower the funds, the coarse the evaluation and I probably less effective actions.

In another study Oleson says that heat stress is the main cause of mortality among humans related to weather. 

But, how we quantify/evaluate a heat-wave (heat-shock, heat-stress)? In 2006 Epstein had already discussed this topic explaining that the assessment of thermal stress and its “translation” to physiological and psychological tension is not easy. There are a number of variables to take into consideration and some of them are not simple to measure or obtain.

Later, in 2015 Freitas again review the topic mentioning 162 thermal indices and Havenith explains the the uses of these indices and modelling have helped to reduce mortality and morbidity in a number of fields as military, sports and other. 

Note 2: With a proper assessment of the heat-stress it would be possible to take measures and do the proper design and adaptation of clothing, houses, stores, factories, hospitals, schools and others like public transportation and hospitals infrastructure for keeping people safe. In case you want to know in the case of Ma already mentioned “Heat waves were defined as ≥2 consecutive days with mean temperature ≥95th percentile of the year-round community-specific distribution”.

In 2012 Coumou et al. mentioned a number of catastrophic events around the world from 2000 to 2011, some of them very expensive other producing a high number of casualties, and they said  that there is strong evidence that those relates to extreme temperature and rain are related with “human influence on climate”.

Note 3: Financial Consequences: This blog is mainly about the effects of the changes in the climate on people´s health, but I would like to emphasize that health is not the only issue associated with heat. There are some literature (Epstein, Dunne) linking this issue with productivity and labour; i.e. an economic aspects that would be affected. Maybe this topic could be the real force making some countries and people to understand that the change is for real and it is not going to be for free for anyone.

How to fight mosquitoes

Being mosquitoes the vectors for malaria and other diseases it is important to understand the way to fight them.

In an article by Harbach and Besansky they explain that only females of some species bite and suck blood from human and other animals as they need this blood for the development of their own eggs; among those blood suckers there is a group of about 100 species that acts as vectors for serious illnesses affecting humans and animals.

Among those illnesses we find (AMCA):

Malaria: About 3.2 billion people are at risk of malaria.

Chikungunya:  Africa, Asia, Indian subcontinent.

Dengue: Asia, Latin America

Yellow Fever: Africa, Central and South America

West Nile Virus:

Zika Virus:

The vector for malaria is the Anopheles mosquito. Eckoff  in 2011 presented a model for this specie including biological and dynamics aspects of the mosquitoes and also human measures to combat them. 

The analysis showed that two actions appeared to be effective: indoor fumigation and nets treated with insecticide.

Note 1: The author of the article is Philip Eckhoff of IDM. I suggest to those interested in modelling and diseases to visit this web that show a lot of interesting work and research.

This modelling seems very interesting and useful, among other things, as a tool to evaluate different strategies against vectors and also to assess the effects of changes in weather conditions (temperature and humidity for example) on malaria spread.

In 2013, appeared a study done in Tanzania by Huho et al. in it the authors found that the majority of the bites occurred indoor, calling for future research to check the effectiveness of different human measures, like the ones already mentioned, to avoid being bitten by mosquitoes. One interesting conclusion was that mosquitoes do not prefer to “eat” indoor but at the time of the day when they prefer to suck most of humans are indoors.

The mentioned conclusion is in line with the findings of Chitnis et al. that in 2012 made another modelling and concluded that fumigation and the use of nets together are the most effective combination reducing malaria. 

They also concluded that once the actions are suspended the original malaria status and indicators can be reached back in 3 years. This sounds perfectly logic as the main measures have the purpose of avoiding the biting not destroying the mosquitoes

Note 2: Nakul Chitnis works in Swiss THP. Another web worth to visit.

Another idea than has been present is the complete eliminations of the mosquitoes. 

In 2013 Killeen et al. wrote an article about the topic explaining the advantages of eliminating mosquitoes over controlling them. They also exposed that the challenges in this procedure were get coverage on proper time and monitoring i.e.

-          - do it fast enough to avoid creation of biological resistance in the animals and

-          - control to avoid any potential re-invasion.

But it seems something is missing in their analysis. This action could create, like climate change, a kind of ecological unbalance. As mentioned by Harbach and Besansky  mosquitoes are food for some other animals and do pollination too, so before evaluating this last alternative it should be clear the potential consequences.

Note 3: Reading an article on BBC about the annihilation of mosquitos a couple of their comments make me think about our right as human to exterminate a specie and the possible consequences of this action. Also it makes me question if all the science is good in a moral sense and if it is valid to incorporate a moral component in science.  These topics are very complex and are not the objective of this blog, but I just wanted to rise the subject.

Getting back to mosquitoes. 

I found that there are a number of institutions and researches all over the world working on the fight against mosquitoes related to malaria and other illnesses. So far, it seems that despite any weather change (than can affect the vectors patterns and behaviours) we as humans have got the tools to combat these insects and avoid or reduce their impact on health, so the question is why there are so many problems in some areas of the world. It could be possible that the answer is the availability of funds. As explained in my last post Europe was declared malaria free, I can imagine after reading the summary of the steps to get there, that this achievement was the result of many years of public policies and actions that for sure would have required a non-negligible amount of direct or indirect funds.

Malaria

In my last post I referred to a report from WHO and WMO, ATLAS OF HEALTH AND CLIMATE, where are mentioned a number of diseases that would be affected in one way or another by climate change, among them Malaria.

Malaria (probably meaning “bad air” as it was thought to be produces by air from marshy areas) is an illness caused by parasites transmitted to humans by specific mosquitoes. There are about 3,500 species of mosquitoes (grouped in 41 genera) (CDC) but it is the female of genus Anopheles which causes the main malarial problem. Malaria is mainly present in tropical and subtropical countries, infecting over 300 million people per year and causing the death of more than 1 million in the same period (MedLinePlus). By the way Anopheles means “useless, hurtful, harmful”

This kind of transmission is denominated vector-borne disease (VBD), i.e. the infectious disease is transmitted to human from another human or from an animal through a living entity (WHO)

From now on I will introduce Notes in my blog, they are trying to aim you, the reader, to check about certain points that seems interesting to me but are not in line with the main course of this blog.

Note 1: if we consider the countries between the tropics we would have about 40% of the total world population and the same percentage of the world´s surface, it would mean that making some very basic numbers the portion of the people infected by malaria between the tropics would be approximately over 10% of the population of the region.

Recent research by Murdoch el al. shows that global warming could reduce the effect of malaria in some regions. They explain that some studies have shown the potential increase of the illness in cooler countries due to the increase in temperature. However, they show that this change, in the warm countries, would reduce the capacity of some of the vectors (the type mosquito carrying the parasite that produces the illness) to act as such and of the parasite itself due to distancing of the optimal temperature conditions. This is very interesting; in case this is proven to be realistic, it would mean that global warming would change the current health/diseases map of the world.

Note 2: Did you know that Europe is the first region in the world to be declared malaria free? WHO says so.

But let´s go back to malaria and climate change, other publications from a number of scientist from Europe and USA of 2015 (Perham et al.) expresses “While this is likely to take many forms (they refer to climate change), the implications for future transmission of vector-borne diseases (VBDs), given their ongoing contribution to global disease burden, are both extremely important and highly uncertain” i.e. the problem is so complex that so far any estimation is very uncertain, meaning they can take any path in the future. For me this is even more dangerous than having a clear consequence as in this last case it is clear what steps need to be followed to overcome the problem and the real possibility of accomplish these steps.  The article mentions a series of challenges/variables/aspects to consider when trying to understand the effect of climate change in VBDs (vector-borne diseases), among them:

1.       Socio-economic and socio-cultural aspects

2.       Selecting the appropriate way of measuring the illness

3.       Data availability

4.       Appropriate models

5.       Ecological aspects

So we have two investigations, one saying that global warming would reduce malaria in a part of the world and the other saying it is extremely hard to know the real effect.

Not being this confusing enough there is another study published in 2014 (Carminade et al.) in it the authors running a series of computational models found that changes in global temperature will favour the transmission of malaria in the tropics but they understand that there are other variables to take into account in future investigations.

If we go deeper in the methodology used by Murdoch et al., we can see they worked under laboratory condition isolating mosquitos from other external variables what makes very difficult to compare it with the other papers and maybe these results should be taking into consideration as a kind of feedback for a major model that includes the mosquito life dynamics.

At this stage I can say that for me the study by Parham et al. seems to express the status of the current climate change – illnesses affair. The problem, not only for malaria but for any vector-borne disease and probably for any other disease, is extremely complex with a great number of variables affecting it and with a high level of uncertainty, making very hard to get a real and quantitative evaluation of future consequences and associated problems.