Matt Ridley from the UK: Malaria, TB and Aids are in steady retreat

There’s a tendency among public officials and journalists, when they discuss disease, to dress good news up as bad. My favourite example was a BBC website headline from 2004 when mortality from the human form of mad-cow disease, which had been falling for two years, rose from 16 to 17 cases: “Figures show rise in vCJD deaths” wailed the headline. (The incidence fell to eight the next year and zero by 2012, unreported.) Talk about grasping at straws of pessimism.

Last week there was a neat example of how good news is no news in the world of public health. Newspapers widely reported a scientific paper, which argued that malaria might get worse in the future at high altitudes as a result of global warming allowing mosquitoes and parasites to survive in higher regions such as Ethiopia and Colombia. Breathlessly, the reports suggested an extra three million people a year might catch the disease.

Did nobody stop to ponder three obvious questions to put this claim in context? First, less than 2 per cent of Africa is too high for malarial mosquitoes. Second, malaria’s distribution shows little correlation with temperature anyway. Lots of tropical countries are free of the disease and lots of cold countries, including Britain and Arctic Russia, have in the past suffered severe epidemics of it. And third, malaria incidence has been not increasing as the world warms but decreasing at a rate of more than five million cases a year for seven years.

The death toll from malaria is falling even faster than the incidence: down by 29 per cent since the year 2000, despite a steadily rising global population. That’s an astonishing bit of happy news about one of humankind’s biggest killers, although 627,000 people still died of it in 2012. One of the places that the authors of the new study say global warming is supposed to make the problem worse at high altitudes is South America. Yet in the whole of the Americas, north and south, there were officially just 800 deaths from malaria in 2012.

In short, the future of malaria depends on bed nets, mosquito control, anti-malarial drugs, better housing and Bill Gates. Temperature is all but irrelevant. Fascinatingly, a statistical study published last year explained not only the current decline but the historic disappearance of malaria from Europe and North America too, largely through the shrinking size of households. The authorsconcluded that “the probability of malaria eradication jumps sharply when average household size drops below four persons”.

The reason for this is that an infected mosquito returns to feed in roughly the same place night after night and its success rate in infecting a new human being is too low for the disease to spread if there are fewer than four people per household. That’s great news, because household size is falling throughout the world, so even without intervention malaria should continue to decline. Yet that study, unlike the altitude one, went largely unreported.

As did the fact that new HIV infections worldwide have fallen by 33 per cent in total, and 52 per cent in children, since 2001. Aids-related deaths are down by 30 per cent since 2005. New cases of tuberculosis have been falling for a decade too, and mortality from TB is 45 per cent down since 1990. Again, these are remarkable and unexpected turn-arounds. Go back to the turn of the century and you will find public health officials uniformly gloomy about the prospects for Aids and TB.

In 2000, for example, the US National Intelligence Council predicted that the burden of HIV/Aids and TB was going to go on getting so much worse for at least ten years that it “is likely to aggravate and, in some cases, may even provoke economic decay, social fragmentation and political destabilisation in the hardest-hit countries in the developing and former communist worlds”.

Meanwhile two truly horrible diseases are on the brink of extinction altogether. Last year there were just 406 cases of polio in the world, mostly in Pakistan, Somalia and Nigeria. Polio’s eradication is long overdue, but it’s getting closer. There has been an even faster decline in guinea worm, a painful parasite that you catch from ingesting water fleas when drinking, and which grows down your leg and erupts from your foot. The only remedy is to pull it out inch by inch over months (I do hope you have finished breakfast).

More than three million people had guinea worm in the late 1980s, when Jimmy Carter made it one of his top priorities. Last year just 148 of the parasites survived, mostly in South Sudan. Despite the civil war there, the eradication work by Mr Carter’s volunteers continues and just three cases have emerged this year. When guinea worm is gone, because it infects no other species, it will be the first deliberate extinction of a living species (smallpox is a virus, and anyway remains in a laboratory). Good riddance.

Not all diseases are retreating. Dengue fever, spread by a different (day-feeding) genus of mosquito from the (night-feeding) malarial genus, is getting steadily more common right across the planet. Antibiotic resistance is complicating the fight against some bacteria. But overall the tropical world is seeing the same huge retreat of infectious death that happened in the temperate world during the previous century.

And nobody seems terribly interested. Why is this? You can understand why journalists don’t tell good news stories more often; their motto, after all, is: “If it bleeds, it leads.” You can be pretty sure that a country that’s gone out of the headlines — Sierra Leone, for example — is doing pretty well.

But why are public health officials not keener to blow their own trumpets? It is, after all, the hard work of dedicated professionals, backed up by millions of volunteers and funded by generous philanthropists, that is driving these contagions out.

Here’s where I turn a touch cynical. A few years ago, maternal mortality — that is, death among women giving birth — began to fall fast, having stagnated for a decade or so. The editor of TheLancet recounted how he came under co-ordinated and determined pressure from women’s health advocates to delay publication of the news of this fall in maternal mortality because, said those pressurising him, “good news would detract from the urgency of their cause”. Aha.

Matt Ridley, a member of the British House of Lords, an acclaimed author who blogs at www.rationaloptimist.com.