The Environment & ‘The Meningitis Belt’
Environmental Change
While for much of this year we have all been swept away by the pandemic and whether life will ever get back to normal - the threat of COVID-19 is also a reminder of other looming emerging and re-emerging diseases in our changing environment. The emergence of COVID-19 itself is undeniably, a product of both natural and anthropogenic change.
Many studies over the past decade have begun investigating the likely health outcomes as a result of climate change in various regions in the world. There is no doubt that it is the most marginalised and economically strained global communities that will suffer the worst consequences of climate change. Now, more than ever, there are multidisciplinary research groups and centres where policy experts, economists, statisticians, microbiologists, climate scientists, epidemiologists, physicians and more are banding together to help the world understand and prepare for future environmental threats to our health. This article will be investigating the threat or lack thereof, of resurging global bacterial meningitis within the context of climate change.
Bacterial Meningitis
Out of all of the bacterial pathogens that cause meningococcal meningitis, Neisseria meningitidis is the most frequent cause of large-scale epidemics across the globe (Streptococcus pneumoniae and Haemophilus influenzae are also relatively common). 6 of the 12 serogroups (50%) of Neisseria meningitidis can cause epidemics, predominantly in young populations (WHO, 2020), but the geographic distribution and epidemic potential varies with each serotype. There’s also some evidence that 10-14-year olds are the most frequent carriers in Africa, in comparison to Europe where the age rises to 19-year olds.
The disease is transmitted from person to person via respiratory droplets from kissing, sneezing, coughing or living in close proximity to an infected person. Once a person is infected, the bacteria can remain in the throat, dormant until it is able to overwhelm the immune system and spread through the blood up to the meninges in the brain. If left untreated, up to 50% of cases can be fatal and studies have found brain damage, hearing loss and/or learning disabilities in 10-20% of survivors (WHO, 2020) (3). This is an ailment of both global mortality and disability.
Although meningitis is observed worldwide, it is concentrated (with over 25k cases per year) in what has been dubbed ‘The Meningitis Belt’ by Leon Lapeyssonie (a French military doctor) in 1963. This is a region spreading from Senegal in the west to Ethiopia in the east of Sub-Saharan Africa, spanning across 26 countries. Although countries surrounding the belt area have also been found to suffer significant burdens of meningitis , it’s not as regular as the burden found in ‘the meningitis belt’. Up to 200,000 people, mainly young children, are affected annually (between February and late May) from bacterial meningitis outbreaks in West Africa . However, there are currently no accurate estimates of global meningococcal meningitis burden due to inadequate and unreliable surveillance in many places. Some research suggests meningitis has similar spatial and seasonal patterns with measles which could be a helpful marker for future control strategies. The last emergency outbreak recorded by the WHO (2020) was in March 2017 in Nigeria and July 2017 in Liberia (associated with attendance at a funeral).
Where the two are interconnected
Sultan et al , were the first to demonstrate the relationship between increased meningitis epidemics and winter in Africa (using Mali as a case study) with most literature confirming this phenomenon. However, while the regular seasonality associated with meningitis has been confirmed, why and how this occurs is still down to speculation. There are currently two academic theories:
1) The increasing rate of dust winds and cold nights in dry seasons (December to June in ‘the meningitis belt’) could increase the burden of general upper respiratory infections in vulnerable populations. The dust winds combined with these respiratory infections can damage the nasopharyngeal mucosa which makes it easier for any N. meningitidis in the throat to overpower the immune system (T. Koutangni et al., 2018; Thibaut Koutangni et al., 2015; WHO, n.d)
2) The increase in overcrowding during colder seasons implies more people in closer proximity to each other- encouraging more successful transmission.
The lack of succinct explanations for the meningitis patterns along the belt makes it impossible to mathematically model future epidemics. A recent study predicted a pattern based on seasonal changes in the regions that are endemic in the rainy season and become hyperendemic during the dry seasons - they only reached epidemic levels when new meningococcal strains enter the population , highlighting the importance of multivariant control.
Furthermore, when investigating these different strains, seroepidemiology studies have found the highest concentrations of meningococcal serogroup A in Ghana (9.09ug/ml) and lowest in Ethiopia (1.43ug/ml). Ethiopia also presents the lowest force of infection (Manigart et al, 2016), suggesting a greater exposure and burden in the western countries of the belt. More recent evidence has built on this, signifying that meningitis epidemics in the belt are shifting eastwards (Zhao et al., 2018) which could be due to the general lack of exposure in the eastern countries. There have also been predictions of the disease spreading more southwards in the Sahelian region (Cote d’Ivoire, Togo, The Central African Republic and Cameroon) due to increased deforestation and desertification towards the south of the Sahel region.
Decreased rainfall, higher temperatures, low humidity and increased abundance of aerosols in the air (dust and particulate matters) have all been proven to drive an increased incidence of bacterial meningitis (Agier et al, 2013.,Agier et al, 2017., Ayanlade et al, 2020., Jackou-Boulama et al,2005., Oluwole, 2015., Wittig et al, 2007). Although it is worth noting that spatial variations in atmospheric dust load were found to have no effect on the incidences of local meningitis epidemics in the meningitis belt in one study (Woringer et al, 2018).
There is also a suggestive effect of wind as well, but that is yet to be explored in more detail (Pérez García-Pando et al, 2014). These environmental changes are on the rise in ‘the meningitis belt’ due to the increased use of arable fields, urbanization and climate change. Though it gets more complicated with suggestions, that it is the interaction of temporary immunity conferred by carriage of the bacteria with the seasonal changes that drives the irregular outbreaks .
Nonetheless, many of these modelling studies should be interpreted with caution as they typically use one country in the meningitis belt as a case study. One study found that while statistical models based only on climate indexes worked well in Niger (showing that 25% of the disease variance from year-to-year in this country can be explained by the winter climate), it failed to accurately represent the disease dynamics in Burkina Faso (Yaka et al, 2008). There are likely even more differences across the region which need to be investigated even further.
Additionally, the same limitation applies to literature on the countries surrounding the meningitis belt. One study suggests there are likely going to be increasing meningitis epidemics with climate change, as has been found in the Democratic Republic of Congo (Mazamay et al, 2020). Whilst others suggest climatic and environmental factors are less influential in shaping seasonal patterns of meningitis in central Africa (Mazamay et al, 2020). Therefore, conclusive evidence is needed to fully understand how surrounding countries in the continent will be affected through environmental change.
Final remarks
Since 2010, the serogroup A meningococcal conjugate vaccine (MenAfriVac) has been introduced via mass campaigns to the populations located within ‘the meningitis belt’. This has successfully reduced the burden of serogroup A meningitis but has also created space for other serogroups to increase in prevalence, specifically serogroup W . Therefore, and although the vaccine campaigns are a key component in controlling the disease, more is needed for elimination and preparedness . Currently, a certified quadrivalent meningococcal vaccination is a visa requirement for Hajj and Umrah pilgrims to Saudi Arabia but with the potential for a new strain to emerge, the transmission would be catastrophic for Muslim pilgrims and populations worldwide.
Understanding the strains throughout the region is critical for guiding surveillance strategies to inform the implementation of future vaccines. It’s crucial to develop affordable, multivalent conjugate vaccines targeting emerging strains and for this, effective surveillance on more local levels is needed . While there have been efforts to map global bacterial meningitis seasonally, there is still lack of a complete surveillance .
Lastly, much of the literature fails to address the biggest contributing factor to bacterial meningitis burden, socioeconomic inequality. Efforts shouldn’t be limited to simple climate change mitigation. Ill-designed houses, destitute living conditions, limited access to schooling and internet, overcrowded sleeping spaces, neighbourhood deprivation and poorly ventilated rooms provide optimum conditions for the bacteria to spread. Furthermore, it creates generations of populations with poor health seeking behaviours and vaccine hesitancy due to an inherent mistrust in authorities and a higher vulnerability to false information .
Climate change is likely going to impact the socioeconomic vulnerability of many agrarian communities, increasing their susceptibility to disease. What is imperative here is to start looking at disease control more holistically and collaboratively. Multisectoral unification is critical to ensure that we can mitigate the worst effects of climate change, especially for marginalised communities who have contributed least to the ailments of our planet’s health.
This article was written by Neelam Iqbal.
Neelam works as an environmental epidemiologist at Public Health England, and is a co-founder of Identity International, a non-profit platform for marginalised voices.
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