午夜福利1000集合

How do you wipe out a disease? (Image: Sven Torfinn/Panos)

We obliterated smallpox 35 years ago, so what will it take to wipe other diseases, like polio and HIV, off the face of the planet today?

ON 12 October 1977, Ali Maow Maalin, a 23-year-old hospital cook in the city of Merca, Somalia, embarked on a journey that would both change his life and mark a moment in history. He encountered a driver in need of directions, and ended up joining him and his passengers to help guide them to their destination, just 15 minutes away.

The passengers were two children. He saw they had rashes and bumps on their face but thought nothing of it. Had he realised the nature of the place he was directing them to, he might have thought twice. A few months earlier there had been an outbreak of smallpox in a nomadic community north of Merca, and health officials were sending suspected carriers to an isolation camp in the hope of stamping out the disease.

That is where Ali was now headed. Afraid of needles, he had never been vaccinated against smallpox. Ali鈥檚 15 minutes of kindness was enough to leave him infected with it 鈥� although unlike millions before him, he recovered. His was the last ever case of naturally occurring smallpox.

Smallpox remains the only human disease to have been deliberately eradicated from the face of the Earth. Defined as the complete and permanent reduction of a disease to zero new cases at a global level, eradication is a challenge to say the least. Even more impressive is the speed with which it was achieved. In 1967, smallpox was responsible for 1.5 million deaths; 10 years later it was gone 鈥� although the official declaration came in 1980.

午夜福利1000集合 benefits aside, there were also sound economic reasons for wiping out the disease. Treating and vaccinating against smallpox, and its impact on the economic productivity of the people who contracted it, cost the world an estimated $1.5 billion each year in the mid-1970s, yet the total cost of the eradication programme was just $300 million. So, more than 35 years on, why does smallpox remain a solo success?

This question has become particularly pressing with the recent resurgence of polio, declared a target for eradication in 1988. 午夜福利1000集合 workers had seemed on course to meet their deadline of stamping it out by 2018. At the start of last year, polio was endemic in just three countries 鈥� Pakistan, Afghanistan and Nigeria 鈥� meaning the virus was circulating in their populations without being introduced from outside. However, the recent civil conflict in Syria means polio is now surging through the Syrian population as well as that of neighbouring Iraq. In the past six months, cases of polio have also cropped up in Ethiopia, Somalia, Equatorial Guinea and Cameroon. Last month, the World 午夜福利1000集合 Organization (WHO) declared polio a public health emergency of international concern.

Smallpox proved that it was possible to eradicate a disease. Why is polio proving so tricky? And might some of the other scourges of our time, from malaria to measles, perhaps even HIV, one day be similarly squashed?

鈥淲hen smallpox succeeded, there were masses of people saying this disease and that disease could be eradicated 鈥� it became ridiculous,鈥� says Donald Hopkins, who directs health programmes at the non-profit in Atlanta, Georgia. The reality is that although many diseases have been discussed as potential targets for eradication, only three have ever been formally targeted on a global scale: malaria, dracunculiasis (also called guinea-worm disease) and polio. Malaria was set as a target for eradication four years before smallpox, but early setbacks such as insecticide resistance stalled progress. Its eradication could soon be back on the table, but until then, efforts against dracunculiasis and polio are all we have at this level.

Even these two campaigns are starting to lag. 鈥淪mallpox was quick once decided,鈥� explains Dina Pfeifer, programme manager for vaccine-preventable diseases and immunisation at the WHO. 鈥淲e are suffering fatigue today because some efforts are taking a long time.鈥�

When the campaign to eradicate dracunculiasis was launched, it seemed a relatively easy target: the parasitic guinea worm was confined to limited regions of Asia and Africa, and simply supplying clean drinking water could, in theory, wipe it out.

People who drink water contaminated with the parasite鈥檚 larvae develop a painful blister on their lower leg or foot about a year later. They often try to relieve the pain by dipping their leg in water, which induces the mature female, lurking in the blister, to burst out and release her larvae. 鈥淚t鈥檚 a disease that no textbook can prepare you for,鈥� says Hopkins. He has been running the WHO鈥檚 eradication campaign since 1986, and was heavily involved in the fight against smallpox before that.

In 1980, at the outset of the dracunculiasis campaign, there were 3.5 million cases of the disease in 21 countries. In 2013, there were just 148 cases reported 鈥� in Chad, Mali, Ethiopia and South Sudan. 鈥淭heoretically, it could be gone by 2015,鈥� says Hopkins, who claims to be immune to pessimism 鈥� an important trait when fighting a tenacious disease. Two deadlines for eradicating it have been missed: one in 1995, another in 2005.

Million dollar search

Often the closer we are to wiping out a disease, the harder it gets. Public health teams can鈥檛 easily access the remote rural areas harbouring the last pockets of guinea-worm infection, assuming they even know where these are. When they do reach them, they may have just one or two cases to deal with, making it a very expensive enterprise for scant returns. 鈥淎 million dollar search in Guinea found only one case,鈥� says Sandy Cairncross at the London School of Hygiene and Tropical Medicine, who helped fight the disease in West Africa in the 1990s. Even some at the Carter Center are alarmed at the costs, but it is important to continue the fight, Hopkins insists. 鈥淚f you leave it now, it will come back and spread.鈥�

This is precisely what is now happening with polio. A war zone, as much of Syria has become, is the perfect setting for such an infectious disease to flourish, as disruptions to health services mean hard-to-reach communities may go unvaccinated. In the case of polio, 80 per cent of the population needs to be vaccinated in order to achieve herd immunity: a state in which it becomes difficult for the virus to spread.

Polio vaccination also poses a challenge in Nigeria and Pakistan. In both countries, conspiracy theories revolving around sterilisation or poisoning by the vaccine have made people suspicious of those delivering the injections, some of whom have been shot at. Educating people about the benefits of vaccination then becomes crucial. In the case of Somalia, Maalin joined the campaign to rid his country of polio. He was able to use his own experience of smallpox as an object lesson in why vaccination was necessary, even convincing some militia leaders it was safe. But it was a case of two steps forward, one step back. After being declared polio-free in 2008, the country reported 194 cases in 2013. Reduced vaccine coverage and then a single infected person arriving from abroad are thought to have sparked the outbreak.

Like smallpox, polio is a viral disease with an effective vaccine that, properly used, can provide lifelong immunity. So why hasn鈥檛 polio been eradicated in the same way?

Military measures

Hopkins became involved in the smallpox campaign straight out of medical school. He believes it worked because it had two key things on its side: a potent vaccine and the support of governments across the globe 鈥� most of which had first-hand experience of grappling with the disease.

But times have changed since the final pockets of smallpox were dealt with. 鈥淔or smallpox they used very military measures, putting people in quarantine with armed soldiers around them,鈥� says Peter Piot, director of the London School of Hygiene and Tropical Medicine. 鈥淚鈥檓 not sure that would work today.鈥�

So to deal with the final pockets of polio, the strategy remains one of trying to vaccinate as many people as possible. 鈥淵ou think you鈥檙e close to the end and then you find a new outbreak,鈥� says Pfeifer. 鈥淲e need to target all immunity gaps to stop transmission.鈥�

For some diseases, eradication may simply be too tough a goal to achieve. But that doesn鈥檛 mean their incidence can鈥檛 be reduced to near zero, at least in some areas 鈥� a strategy known as elimination (see 鈥�A world without HIV?鈥�). And elimination can itself pave the way for eradication, by proving to governments and funders that it is possible to rid entire areas of a disease.

Measles is one disease being targeted for global elimination by 2020. Once again, an effective vaccine exists, although 95 per cent of the population needs to receive it in order to stop the virus from spreading. That鈥檚 a far higher proportion than with any other disease. On the other hand, measles is easy to diagnose, it only infects humans, and once vaccinated, you鈥檙e immune for life.

So why are we not being more ambitious? 鈥淚t is biologically feasible to eradicate measles,鈥� says Peter Strebel from the expanded programme on immunisation at the WHO. Measles has already been eliminated in the Americas, with the last endemic case in 2002; any cases since then have been the result of people arriving from abroad. But as long as measles exists elsewhere 鈥渢here is always a risk of importation鈥�, says Strebel, especially with today鈥檚 level of global travel. It is also difficult to run several eradication programmes in parallel. With efforts against polio still ongoing, now is not the time to be setting a date for measles eradication, Strebel says.

鈥淚t is biologically feasible to eradicate measles. But it is difficult to run several eradication programmes in parallel鈥�

Global elimination of measles by 2020 would in itself be a massive achievement. One definition of elimination is slashing the incidence of a disease until it is no longer a public health burden. In theory, this should protect those pockets of the population who choose to remain unvaccinated, for example, because of fears that the vaccine causes autism.

What about malaria? Is there any hope of eliminating it over time, or even wiping it off the face of the Earth? The original campaign to eradicate malaria was launched in 1955, although the US had begun its own campaign to stamp out the disease nine years earlier. It seemed to be working; by 1951, the disease had been eliminated from all 50 states. Similar successes were seen in Europe.

Yet these efforts, which mainly relied on the use of insecticides, failed when attempted globally. Even small gaps in insecticide coverage enabled mosquitoes carrying the malaria parasite to survive and re-establish themselves. The plug was finally pulled on the project in 1968.

When aiming to remove a disease completely, a vaccine is a massive bonus. 鈥淵ou need a simple intervention, and a vaccine is still our best bet,鈥� explains Piot. 鈥淲hen there is heavy transmission, even an imperfect vaccine can make a difference.鈥�

The recent success of malaria vaccines in clinical trials has brought some hope. For example, the RTS,S vaccine builds up antibodies that block malaria parasites from gaining a foothold in the body. Although only partially effective, its arrival, combined with other strategies such as bed nets and mosquito control, has put talk of malaria eradication 鈥� or at the very least, elimination 鈥� back on the table.

In 2007, the African Union launched the African Malaria Elimination Campaign, with the aim of reducing infections to zero in countries with low rates, such as Botswana 鈥� as well as reducing deaths and illness by 75 per cent in countries where the disease is more common. The strategy involves intensifying measures such as the distribution of insecticide-treated bed nets and, as with all disease control, requires continuous political support.

Back to Somalia and Ali Maalin, who fought against polio quite literally to his death. In July 2013, Maalin was out on a polio vaccination campaign in Somalia, during its surge in reinfections, when he fell ill and died 鈥� reportedly of malaria. In his life, he witnessed the eradication of one disease and the near-eradication of two others. Perhaps the rest of us will live long enough to see these 鈥� and perhaps other diseases 鈥� similarly obliterated.

This article appeared in print under the headline 鈥淓very last trace鈥�