The environmental cost of Saharan dust in West Africa: Lower life expectancy

Last week I returned from a two week visit in Senegal, with a goal of finishing up a project but also continuing my quest to understand how dust from the Sahara may be impacting the health of people, but especially those who are vulnerable (young, elderly and those with Asthma).   The Sahara desert is the world's largest desert with approximately 800 billion to 1.4 trillion pounds of dust transported from the desert each year.  From the months of December through April this dust can race along the ground creating fog like conditions, while during the summer it is normally located above the ground some 2000-5000 feet above the ground. 

There are three health aspects that I have been chasing over the last year (1) The linkages between Saharan dust and Meningitis; (2) The seasonal impact of dust on Asthma, COPD and other respiratory diseases; (3) The mystery of the dust haze around Dakar.

First the basics.  Saharan dust has a size range of 0.1 microns (0.0000001 meter) (ultrafine) to probably 20 microns (giant) with most of the particles falling between 1-10 microns.  By comparison a human air has a diameter that can be 80-100 microns which means that dust particles are 5 times to 100 times smaller than a human hair The closer that you are to the source, the larger the particles are more likely to be.  The small particles can be suspended or carried for thousands of miles downstream -- for example to the Caribbean or the United States.

The large particles (known as PM10) have a negative impact on the upper respiratory tract.  You breath them through in through your nose and mouth.  Your natural defenses such as the hair in your nose has the ability to trap a portion of these particles.  Quite often, you will develop a cough in the presence these large particles, but when they are abundant, the visibility is limited and it looks like a fog -so it is visible.

Upper Respiratory Tract where PM 10 particles have their greatest impact.

The smaller particles (known as PM2.5) have a negative impact on the lower respiratory system, because these particles are smaller and evade the filtering system of the nose.

Lower Respiratory System where PM 2.5 or smaller particles have their greatest impact

The smaller particles can enter into the lungs and inhibit the ability to breath.  Hence people with Asthma, Bronchitis, Emphysema and COPD are often negatively impacted.

Finally, the ultra-fine particles (0.1) microns can enter deep into the respiratory system and may even be able to enter into cell structures.  There is not much known about the effects of ultrafine particles on human health, but studies with rats should that they negatively impact the ability of the rats to breath and there are tumors that often form around the sites where the particles are interacting with the cells. These ultra-fine particles can be either single or form as groups (aggregates).

1. The linkages between Saharan dust and Meningitis

Key facts about Meningitis from the World Health Organization

Young boy suffering from Meningitis (WHO)

• Meningococcal meningitis is a bacterial form of meningitis, a serious infection of the thin lining that surrounds the brain and spinal cord.
• The meningitis belt of sub-Saharan Africa, stretching from Senegal in the west to Ethiopia in the east, has the highest rates of the disease.
• Group A meningococcus accounts for an estimated 80–85% of all cases in the meningitis belt, with epidemics occurring at intervals of 7–14 years.
• In the 2009 epidemic season, 14 African countries implementing enhanced surveillance, reported 88 199 suspected cases, including 5352 deaths, the largest number since a 1996 epidemic.
• Several vaccines are available to control the disease: a meningococcal A conjugate vaccine, C conjugate vaccines, tetravalent A, C, Y and W135 conjugate vaccines and meningococcal polysaccharide vaccines.

WHO suspected cases of Meningitis across the Meningitis Belt 

The disease, Meningitis, is transmittable through contact, such as sharing of utensils or kissing.  The time for the disease to manifest itself is 2-14 days after contraction.  The disease has been impacting young people under 20 years of age in Senegal and is often difficult to diagnose, especially in young children where it may be viewed as flu, because aches and pains are often associated with the flu.  In addition, spinal fluid must be extracted from potential patients to confirm Meningitis.  Many people in Senegal have been vaccinated for the Group A serotype, but in fact it is the strain of W-135 which is on the rise in Senegal.   The poor health care system in Africa, where doctors are not available to treat patients means that there is still 10-20% fatalities with the disease.

The question is why is occurs in these various intervals and what is the role of the environment.  Quite often religious pilgrimages to Mecca or Touba (in Senegal) where lots of people are together from different backgrounds will be associated with Meningitis outbreaks.   It is believed that  some portion of the population is carrying the bacteria in their throat at any given time.  The question is what triggers the outbreaks.


From an environmental point of view, dry air and winds from the north have been reported to be linked to Meningitis outbreaks.  However, in my opinion, dust is the most likely environmental cause related to Meningitis.  I say this because:  (1) large dust storms force people inside making transmission more likely; (2) Coarse or giant particles are likely to destroy tissue in the Nose and NasoPharynx making one more susceptible to Meningitis; (3) The dust may carry other pathogens (bacteria, virus, fungus) which can make one more susceptible to Meningitis.

Upper Respiratory system and Nasopharynx

In Senegal, we have seen an uptick in the number of suspected cases of Meningitis since 2010 with approximately 1400 suspected cases being identified during this time.  The majority of these cases are Sero-type W135 and more than 80% are occurring for people under 20 years of age.  In 2012 for example, there was a suspected 894 cases, but we have also found that dust concentrations were considerable higher in 2012 relative to 2013 or 2014.  With the help of the Ministry of Environment and dust models were are going back trying to reproduce the dust events during these two years and the results are very promising and will be submitted to peer review for publication.


2. The seasonal impact of dust on Asthma

At present, there are no studies in Sub-Saharan African which have linked dust to Asthma.  PM2.5 is a serious source of the problem for Asthma and based on both measurements and modeling.   I believe that is has a 2 period of the year when it is problematic.  The first period is during the winter/spring where heavy dust storms come into the region and air quality if poor for everyone.  The second time is from May through September where the dust from the Sahara rises above the Monsoon layer but slowly falls out as it is transported towards the Caribbean.  

While both periods are dangerous, it is the second one that is less obvious to the average person.  The dust is suspended at 2000-5000 feet above the ground and not in your face but you have to look up to the sky.   When dust is overhead, the sky looks milky white.

Dust Storm over Dakar, Senegal on July 1, 2010

However if you were flying above this dust, it takes on a different look.  It looks brown and you know that you hit JACKPOT --- Dust from the Sahara.

Flying over Sahara Dust between Cape Verde and Senegal.

Based on our analysis of data from the lab for atmospheric physics in Dakar, the dust size for summer dust events is 1-2 microns, which means that it is a hazard to the lower respiratory system...and especially those with Asthma.

One of my very good friends in Senegal is Mariama.  I have know her and her family members for more than a decade.  She has a daughter named Adja who will be 3 soon and is just so lively.

Mariama and Adja 

Me and Adja 

Mariama has Asthma and she tells me that Adja is a good candidate for Asthma unless she has an operation to address some issues as it relates to her upper respiratory system.  She working to gather the funds for the operation.    Just a few days (June 10) after visiting Mariama's family a dust event from the Sahara arrives over Dakar.

June 10 Saharan dust event over Senegal

I called Mariama because I left my Philly's hat there (gotta keep the Sun off my head).

Mariama did not pick up and the next day that I spoke to her, she told me that she had an Asthma attack and could not speak.   When the dust event was over Dakar, the air became heavy and your skin had the feeling of dust on it, even though you could not see it.  We were monitoring from the lab and knew that it arrived.

In speaking to Dr. Toure at the local hospital she also believes that there is a double season for Asthma based on the patients coming in with acute respiratory problems.  The problem is that the country wide impact of dust and asthma are unknown but there is an effort to organize and collect relevant data.

3.  The mystery of the dust haze around Dakar. 

 Over the last 3 years we have noticed a haze over Dakar which we capture from the Ceilometer on the roof.  It was here is 2012, it was around when President Obama came to visit Senegal in 2013 and it is around it 2014.

Haze over Dakar looking downtown

We have tried to determine, where the dust is coming from, the sizes of the particles and why it is trapped near the ground based on the ceilometer.  

Our recent findings are:

1.  We now have high confidence that the dust is coming from Western Sahara and Morocco and coming down the coast and coming into Senegal.

2.  We now are confident that these are ultrafine particles of 0.1-0.3 microns in diameter.  

3. We do not know why these particles are trapped near the ground but they pose a health rise because they can penetrate deep into the lungs and possibly into human cells.  

My most recent visit to Senegal was probably the most fruitful, because I spoke to colleagues across various disciplines and we are developing a strategy for prediction, warning and treatment respiratory issues that arise from Saharan dust.  We know that millions of persons are being negatively impacted by Saharan Dust in West Africa.  It is time be part of the solution because the environmental cost is high:  Poor health and lower life expectancy.   We all deserve good health.  

Stay tuned