Wednesday, 23 September 2009

Tropical enteropathy − 3

OK, now for an enterology lesson! In a healthy gut (actually the small intestine − see first figure below) there are tiny, finger-like projections called ‘villi’ that allow the body to absorb nutrients from the food we eat into the blood − the average healthy villus is around 1.0 mm long and around 0.5 mm in diameter.

This figure shows the villi in a healthy gut:

In a child with tropical enteropathy the villi become inflamed and flattened − this is termed ‘villous atrophy’ (see next figure below). With the villi damaged in this way, the body can’t properly absorb all the nutrients from food − a process called ‘malabsorption’.

This figure shows a photomicrograph of healthy villi on the left and one of atrophied villi on the left:

[First three figures from here; last from Google Images here.]

And this is a slightly more detailed explanation (from here):

Good health requires proper digestion and absorption. Digestion is the mechanical and chemical breakdown of the food we eat. As food is digested it needs to be absorbed. Absorption is the process of bringing the nutrients from our gastrointestinal tract into the rest of our body’s tissue. Digestion is initiated when we chew food and begin to break it down with digestive enzymes. Food then enters the stomach where further breakdown occurs due to the presence of hydrochloric acid and pepsin, which together begin the breakdown of proteins. From the stomach the products of digestion enter the small intestine.

The small intestine is called “small” because it is smaller in diameter than the large intestine. However, it is in fact longer and in many ways more crucial to our health than the large intestine. The lining of the small intestine consists of villi − finger-like projections that stick out from the wall of the intestine into the lumen. These villi are between ½ and 1½ mm long, just barely visible to the human eye. On the ends of the villi are microvilli. These two adaptations, villi and microvilli, increase the surface absorption area of the small intestine up to 1,000 fold. It’s estimated that the entire absorptive area of the small intestine is roughly the size of a basketball court
[i.e., ~435 sq. m − amazing!].

This total area for absorption can be compromised by any condition that irritates the lining of the small intestine. This leads to poor digestive function and affects many vital structures on the intestinal wall. Inadequate absorption of nutrients is referred to as malabsorption − the inability to get the vital nutrients your body needs delivered to your cells.

So, if a child has malabsorption then most of the nutrients in the food (s)he eats just passes through and out. Thus malabsorption → malnutrition → low weight-for-age and low-height-for-age → impaired cognition and then reduced productivity in adult life. Exactly what’s not needed for socio-economic development in developing countries.

Saturday, 19 September 2009

Tropical enteropathy − 2

It’s difficult for an engineer like me to understand exactly what tropical enteropathy is. There’s a reasonably informative entry on ‘Malabsorption syndromes in the tropics’ on pages 600−603 of volume 2 of the Oxford Textbook of Medicine, 4th ed. (OUP, 2005). You should be able to read these pages on Google Books here. I’ll keep looking for an even more understandable explanation.

Global health

In International Health, a new journal launched this month by the Royal Society of Tropical Medicine and Hygiene, Richard Horton, the distinguished (and indeed controversial) editor-in-chief of The Lancet, has written a highly erudite paper which is an excellent and important read: Global science and social movements: towards a rational politics of global health (free access to the pdf as it’s in the very first issue of the journal).

Houses, mosquitoes, and evolutionary control

This week’s issue of The Lancet has two interesting papers on mosquito control: a ‘Comment’ paper: House screening for malaria control, and a full paper Effect of two different house screening interventions on exposure to malaria vectors and on anaemia in children in The Gambia: a randomised controlled trial. Both worth reading. But Professor Paul Ewald of the Department of Biology at the University of Louisville, in his 1994 book Evolution of Infectious Disease (OUP), was ahead of the game: read the section ‘Evolutionary control’ on pages 53−55 of the book on Google Books here. And you can watch his 2007 Ted Talks lecture Can we domesticate germs? on the evolutionary control of diarrhoeal disease pathogens and also on mosquito-proof houses − very thought provoking!

Friday, 18 September 2009

Tropical enteropathy

The Lancet has published today a really relevant ‘Viewpoint’ article: Child undernutrition, tropical enteropathy, toilets, and handwashing by Dr Jean Humphrey (of the Center for Human Nutrition, Johns Hopkins Bloomberg School of Public Health in Baltimore, MD and the ZVITAMBO Project in Harare). The article starts off in a pleasingly forthright way:

Of the 555 million preschool children in developing countries, 32% are stunted and 20% are underweight. Child underweight or stunting causes about 20% of all mortality of children younger than 5 years of age and leads to long-term cognitive deficits, poorer performance in school and fewer years of completed schooling, and lower adult economic productivity.

The hypothesis of the paper is simply:

that a key cause of child undernutrition is a subclinical disorder of the small intestine known as tropical enteropathy, which is characterised by villous atrophy, crypt hyperplasia, increased permeability, inflammatory cell infiltrate, and modest malabsorption [details here]; that tropical enteropathy is caused by faecal bacteria ingested in large quantities by young children living in conditions of poor sanitation and hygiene; that provision of toilets and promotion of handwashing after faecal contact could reduce or prevent tropical enteropathy and its adverse effects on growth; and that the primary causal pathway from poor sanitation and hygiene to undernutrition is tropical enteropathy and not diarrhoea [emphasis added].

Dr Humphrey concludes her Viewpoint with:

Undoubtedly, the complex problem of child undernutrition will not be solved with toilets and handwashing alone. Interventions focused on gut microbial populations and improved drinking water quality might be important, together with continued efforts to improve infant diets. However, I hypothesise that prevention of tropical enteropathy, which afflicts almost all children in the developing world, will be crucial to normalise child growth, and that this will not be possible without provision of toilets. Randomised controlled trials of toilet provision and handwashing promotion that include tropical enteropathy and child growth as outcomes will give valuable evidence for this premise, and might offer a solution to the intractable problem of child undernutrition [emphasis added].

The African Report on Child Wellbeing: 2008 has some relevant quotes (the whole report is excellent − I’d not come across it before yesterday: it’s really quite disturbing):

Despite some progress, life for millions of Africa’s children remains short, poor, insecure and violent (page 90),

Too many children die needlessly before they reach the age of five, and too many have no access to health and medical services, adequate nutrition, safe water and improved sanitation services (page 11),

The best way of combating child death is to improve and expand access to primary health care, nutrition and improved water supplies, sanitation and hygiene – therefore to increase the budget allocated to public health (also page 11).

In August this year The Lancet had an excellent ‘Comment’ article: Child survival and IMCI: in need of sustained global support. Here’s a quote:

The broader determinants of child survival are crucial to understanding the potential effect of any set of interventions and the obstacles to reducing child mortality. An analysis of data from 152 countries [abstract here] noted that gross national income per head, female illiteracy, and income equality predicted 92% of the variance in child mortality. In low-income countries, where most child deaths occur, female illiteracy was more important than was gross national income per head, and both were more important than was public expenditure on health. A study from The Gambia [pdf here] showed that community and social networks, personal support for caregivers in the home, and financial autonomy were more important determinants of child mortality than was access to health services. Improvement of the quality of care in primary health clinics and referral hospitals will be essential to increase child survival, but as Arifeen and colleagues’ study [abstract here] shows, these interventions alone will be insufficient. Improvement of education of girls, social supports and networks for parents, economic equity, and sustaining broad-based maternal and child health services are all parts of what is necessary to reach targets for Millennium Development Goal 4. [MDG4 is to ‘Reduce child mortality’ − 2008 UN fact sheet here].

So the message: clean up the environment, especially the immediate domestic and peri-domestic environment, by the provision and sustained use of sanitation and handwashing facilities, educate girls, and put public health right up very high on the political agenda. Fingers crossed − it could just work, especially if politicians, civil servants and local-government employees were to get off their asses and on with their job.

And here’s a brilliant quote from the paper International Efforts to Control Infectious Diseases, 1851 to the Present (published in the Journal of the American Medical Association in September 2004):

Public health is ... an investment that works best when purchased in advance rather than paid out as each crisis arises.

Quite. But the trick is to get those politicians to understand this, and understand it fully.

I’m indebted to the authors of the April 2009 World Bank Policy Research Working Paper No. 4907 How Can Donors Help Build Global Public Goods in Health? for this quote. This policy paper is very well worth reading in its own right − here’s its Abstract:

Aid to developing countries has largely neglected the population-wide health services that are core to communicable disease control in the developed world. These mostly non-clinical services generate “pure public goods” by reducing everyone’s exposure to disease through measures such as implementing health and sanitary regulations. They complement the clinical preventive and treatment services which are the donors’ main focus. Their neglect is manifested, for example, in a lack of coherent public health regulations in countries where donors have long been active, facilitating the spread of diseases such as avian flu. These services can be inexpensive, and dramatically reduce health inequalities. Sri Lanka spends less than 0.2% of GDP on its well designed population-wide services, which contribute to the country’s high levels of health equity and life expectancy despite low GDP per head and civil war. Evidence abounds on the negative externalities of weak population-wide health services. Global public health security cannot be assured without building strong national population-wide health systems to reduce the potential for communicable diseases to spread within and beyond their borders. Donors need greater clarity about what constitutes a strong public health system, and how to build them. The paper discusses gaps in donors’ approaches and first steps toward closing them.

[The only thing I’d add is that many, if not most, developing-country governments also “need greater clarity about what constitutes a strong public health system, and how to build them”, not just donors.]

And it starts with another good quote:

Focusing on clinical services while neglecting services that reduce exposure to disease is like mopping up the floor continuously while leaving the tap running.

HARDtalk: Helen Clark

HARDtalk, the BBC programme showing “in-depth interviews with hard-hitting questions and sensitive topics being covered as famous personalities from all walks of life talk about the highs and lows in their lives”, today features an interview with Helen Clark, the head of UNDP (and former prime minister of New Zealand), on the Millennium Development Goals. The programme blurb is: “In September 2000, the Millennium Declaration was ratified. One hundred and eighty nine nations committed themselves to the Millennium Development Goals - a plan to reduce poverty, tackle hunger and improve education and healthcare by 2015. Jon Sopel talks to Helen Clark, the woman tasked with delivering this on behalf of the United Nations. But how much progress has been made and can these sweeping targets ever be achieved?” It’s available here for the next 12 months. Well worth watching.