Tuesday, May 20, 2014

Fiddling with genes while Rome burns

By Anne Buchanan and Dan Parker

There's a new paper in PLOS Neglected Tropical Diseases ("The Gulf Coast: A New American Underbelly of Tropical Diseases and Poverty", Hotez et al.), describing the increasing prevalence of infectious tropical diseases among poor people living on the US Gulf Coast, an area of the United States ripe for the spread of diseases that have until recently only been found in tropical countries.  It is ripe for such diseases because much of the region has a subtropical climate and several potential insect vectors of infectious disease.  For much of recent history though, there has been very little insect-borne infectious disease in this area, although such diseases were once highly prevalent.

And, a paper in Science last week ("Crippling Virus Set to Conquer Western Hemisphere", Enserink) tells of the spread of a currently emerging infectious disease, chikungunya, which is communicated by the Aedes aegypti mosquito (also a vector of dengue fever) which is found throughout much of the world.  The virus has made its way to the Caribbean and thus is expected to soon be found from the southern US to southern Latin America.

The World Health Organization identifies 17 "neglected tropical diseases".  We neglect neglected diseases at our peril.  Or, not specifically our peril -- the peril primarily of poor people.  Extreme poverty and a warm, tropical climate are the two most potent forces promoting the endemicity of neglected tropical diseases in Africa, Asia, and Latin America. Now, these same forces are also widely prevalent in the five states of the US Gulf Coast—Texas, Louisiana, Mississippi, Alabama, and Florida. Poverty is rampant: ten million Gulf Coast residents currently live below the US poverty line, with Mississippi topping the list of all states in terms of percentage of people who live in poverty (22%). Texas alone has almost five million poor people. Tropical diseases such as dengue, malaria, typhus, cholera, yellow fever, chagas disease and others once found in the US but eradicated with economic development, are neglected by global health organizations and Big Pharma because poor countries and poor people can't afford the drugs to treat them. Pharmaceuticals are corporations and therefore have little incentive to develop such drugs.

More than a billion people around the world suffer from one or more neglected tropical diseases.  PLOS Neglected Tropical Diseases describes these diseases this way:
The NTDs are defined as a group of poverty-promoting chronic infectious diseases, which primarily occur in rural areas and poor urban areas of low-income and middle-income countries. They are poverty-promoting because of their impact on child health and development, pregnancy, and worker productivity, as well as their stigmatizing feature.
Chikungunya is spreading rapidly in the Caribbean.

Island hopping. 
Chikungunya, whose main vector is the Aedes aegypti mosquito, is spreading fast in the Caribbean. Science.

The virus can cause rashes, fever, and intense, sometimes lasting joint pain.  Infected people sometimes arrive at health centers with their arms locked in flexion from the pain in their elbows and other joints.  Millions will likely get sick with this disease.

The virus has been spreading through Africa and India for about a decade, and a recent genetic variant allows it to be spread by a second vector, A. albopictus, the Asian tiger mosquito, which has expanded its territory greatly in the last three decades, including through southern Europe.  While mosquitoes bite rich and poor alike,  and in theory everyone in areas where the tiger mosquito or A. aegypti are abundant is at risk of chikungunya, in practice mosquitoes are more likely to breed in areas with standing or stagnant water, in old tires, along streets with no rainwater drainage, or areas with no mosquito control, so it's likely that this disease will disproportionately affect poor people wherever it spreads.

And certainly along the US Gulf Coast it's the poor who are at increased risk of the diseases that are now increasing in prevalence there; dengue fever has been in Texas for at least 10 years, and was identified in Houston and South Texas in 2013, with the poorest communities most affected.  Typhus, encephalitis, trichomoniasis, Chagas disease, helminthic infections, and diseases that have been rare or absent for decades have also been documented in Texas, primarily in African American and Hispanic communities. Many of these diseases are especially high risk for pregnant woman and infants.  And, diagnosis and treatment is often lacking, and local physicians not knowledgeable about the diseases.

The social and economic impact of these diseases on the southern US could be significant.  Perhaps given that they are now so close to home, they will begin to attract research dollars and interest - already a National School of Tropical Medicine has been established at Baylor College of Medicine in Waco, Texas. After a rather hubristic few decades or so when we in the West believed we had conquered infectious diseases, the HIV/AIDS epidemic woke us to the fact that infectious diseases aren't going to go away.  Increasing antibiotic resistance and the fact that, with global travel, many diseases can spread almost instantaneously -- MERS, for example, has now been diagnosed in three people in the US, including one infected here rather than in the Middle East -- neglected diseases should no longer suffer such neglect.  Will this happen?  Is the new school at Baylor an aberration?  If the diseases continue to primarily affect the poor, it's hard to be optimistic.  Developing vaccines is costly and Big Pharma prefers investing in drugs that people take for the long haul -- statins, Viagra, blood pressure meds -- rather than drugs to treat infectious diseases in the short term.

For that matter, the big research dollars go to sequencing viruses and parasites, generally neglecting the social aspects (like poverty) that lead to these conditions, even while we all acknowledge the strong links between poverty and tropical diseases.  Given the increasing spread of infectious diseases in a warming climate, it may well turn out to have been pretty foolish to have spent billions of dollars on genetics research at the expense of infectious diseases.

1 comment:

joseph muita said...

Tropical and infectious diseases remain the most important health problems in developing countries. In children, measles, diarrhoea, malaria and acute respiratory infections kill millions worldwide whereas in adults, sexually transmitted diseases, HIV/AIDS, parasitic and other protozoal infections, tuberculosis and malignancies associated with viral infections are major causes of morbidity and mortality.
The impediments to the control of these diseases in developing countries are many. For many immunizeable diseases, solutions exist but have not been implemented for financial or logistical reasons; for others such as waterborne diseases, we have solutions but do not yet know how best to apply them; and for a third category such as HIV/AIDS, solutions remain a hope for the future.
The ultimate control can be achieved through further research on identifying novel strategies for control of these diseases in developing countries and on implementing effective intervention programmes fully integrated with other health programmes.