Thursday, November 19, 2009

Why It’s a Good Thing That Dennis Had Malaria Last Week*

*Disclaimer: This blog takes a very simplistic stance on the very complex topic of malaria endemicity. I would like to personally apologize to any public health professionals who may be reading this. Also, with a sample size of 1, a more appropriate title would be: “Why It Could Be Seen As a Good Thing That Dennis Had Malaria Last Week.” But that title isn’t as catchy.

It can be the very definition of growing pains. And something that can be tricky to explain to those who don’t deal with it every day; so let me have a go at it:

In areas of high malaria transmission, individuals are bitten by infected (vector) mosquitoes on a constant basis. This is an enormous problem for children and pregnant women, but by adulthood, an acquired immunity is developed whereby the malaria parasite (usually Plasmodium falciparum) is always in the bloodstream, and each additional exposure to the vector (aka: mosquito bite) rarely results in an episode of clinical malaria. This scenario is euphemistically termed “stable malaria”.

In areas of lower transmission, individuals are bitten by infected mosquitoes less often, and the amount of malaria parasite in the blood stream fluxuates. This is a somewhat better situation for children and pregnant women; however, immunity is not acquired in adulthood, at least not as consistently, and each new vector exposure leads to an episode of clinical malaria more often. This scenario is called “unstable malaria”.

Now, it may seem like both scenarios have their pros and cons, and one is not necessarily better than the other, but lower transmission is certainly better than higher. (Think of which one is better for the women and children, sort of like a Titanic/life boats situation…They are more important and get saved first.) And the end goal of all malaria programs is eradication: the elusive E word. In order for that to happen, areas of high malaria transmission will have to become areas of lower transmission before they can become malaria-free areas. Alas, for my friend Dennis, these growing pains can be literal pains indeed. (Though he seems to be smiling now.)

A somewhat related “growing pains” type of situation worth mentioning is one from the field of HIV/AIDS that my old CGD colleague,
Mead Over, an expert in AIDS economics, deals with on a daily basis. It has to do with the difference between incidence and prevalence, and the fact that, counterintuitively, higher HIV prevalence rates can undoubtedly be a good thing. Incidence refers to the amount of people newly diagnosed with a disease over a certain period of time; a lower number here is almost always better**. Prevalence, on the other hand, refers to the number of people currently living with the disease. And for HIV/AIDS, the main goal right now is increased access to ART (antiretroviral therapy). Thanks to the great advancements in these HIV drugs, people are now able to live much longer lives with the disease. And higher prevalence rates – more people living with the disease – means more people not dying from it. Seems straightforward enough, but it still causes headaches for Mead and other AIDS experts dealing with policymakers doling out the money.

**Higher incidence rates can also be a somewhat good thing if great strides have been made in the number of people being tested for a disease. Obviously, it is not a good thing that more people have the disease, but it is better that the higher burden is now known by public health professionals. This happened recently when the HIV/TB co-infection rate jumped from 1-in-8 to 1-in-4 almost overnight.

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