DAKAR, 14 February 2011 (IRIN) - Researchers are analysing dust from the Sahel to study its role in the spread of bacterial meningitis in this region hardest hit by the debilitating and often fatal disease.

Study of the link between climate and infectious diseases is increasingly important as environmental changes appear to be pushing the so-called meningitis belt - from Ethiopia to Senegal – southwards, experts say.

Researchers with the International Research Institute for Climate and Society (IRI) at Columbia University, which looks at how climate information can be incorporated into preventive measures or early warning systems, are collecting dust samples in Ghana, Niger and Senegal in the study's initial phase.

In the meningitis belt meningococcal meningitis outbreaks come with the dry season and taper off with the first rains, and dust has long been seen as contributing to the spread. Experts say mineral dust could be irritating membranes making people vulnerable to infection, or in other ways favour the spread of the bacteria.

"The mechanism by which dust may influence meningitis epidemic occurrence remains unclear," IRI senior research scientist Madeleine Thomson told IRIN. "But the most common explanation for this role is that physical damage to the epithelial cells lining the nose and throat in dry and dusty conditions permits easy passage of the bacteria into the blood stream."

The study will further probe the dust's characteristics. "We will look at the properties of the dust and other climatic and environmental variables and determine whether, or to what extent, they influence the spatial and temporal occurrence of either carriage [when bacteria are present in the nose and throat but are non-invasive] or disease [when the bacteria are in the bloodstream]," Thomson said.

Researchers must also consider other potential mechanisms, said Thomson. For instance, she said, dust particles may impact the fluid dynamics of airborne transmission of the bacteria as well as preceding viral infections, and the high iron content of Sahelian dust may help activate the iron-hungry meningococcus bacteria.

High dust levels might also affect human behaviour: Crowding in small rooms with windows blocked can reduce ventilation, and facilitate transmission. Dust could also have an impact on other climatic variables, such as temperature and humidity, which may also be important drivers of meningitis infection and disease, Thomson explained
While several diverse factors play a role in bacterial meningitis outbreaks, an understanding of how the dust might be affecting people's vulnerability can significantly boost prevention efforts, experts say.

In support of vaccine strategies

The dust research adds to a broader international World Health Organization-led project called MERIT (meningitis environmental risk information technologies), which is designed to support current vaccine strategies as well as the African Meningoccocal Carriage Consortium (MenAfriCar), and the distribution of the new proactive vaccine currently being rolled out in West Africa. The new vaccine provides 10 years of protection as opposed to two or three.

Meningococcal disease - bacterial meningitis - occurs throughout the world, but attack rates in the meningitis belt are many times higher than those in other parts of the world. Death rates are generally 5-10 percent, according to MenAfriCar. The disease can also cause blindness, hearing loss, brain damage and loss of limbs.

The dust study is being funded by the NIEHS Center for Environmental Health in Northern Manhattan and by a grant/cooperative agreement from the US National Oceanic and Atmospheric Administration.

IRI's Thomson said interdisciplinary research into such burdens in poor countries is particularly difficult to fund, but that study of climate-sensitive infectious diseases like meningitis and malaria is increasingly important. "Climate and environmental change have the potential to impact on the effectiveness of disease control programmes," she told IRIN. "For instance, there is a major concern that changes in the climate and environment are pushing the meningitis belt southwards; if this is the case there will be important implications for the development of meningitis control strategies."

Burden

While meningitis is not the top killer disease in the Sahel, the frequent, major epidemics deal a heavy blow to health systems and to families and communities.

"Meningitis not only kills, it maims," IRI's Francesco Fiondella told IRIN. "It has long-term impacts on society. It draws resources from families and societies when people either die from the disease or become deaf or blind or lose a limb."

Kandioura Touré, head of epidemiological surveillance and infectious illness in Mali's Health Ministry, said meningitis is a constant burden and any progress in reducing cases has a huge impact.

"Meningitis weighs heavily not only on families - with deaths and cases of deafness and other disabilities - but also on the health system," he told IRIN. "Each year we face these epidemics."

Mali is one of three countries where the new vaccine is being rolled out. "These efforts give us hope we can finally eliminate the burden of this disease," Touré said.

Source: The Integrated Regional Information Networks (http://www.irinnews.org )