In recent years, South Asian countries have beaten down infectious diseases like malaria, polio and lymphatic filariasis. These public health victories are the result of sustained policies, investments and hard work that are worth celebrating — and sustaining.
Public health programmes need to guard against complacence and re-introduction of disease-causing microbes, which can easily happen in this age of globalised travel and goods transport.
When beating back a persistent infectious disease appears within reach, governments must ensure policy priority and adequate funding for the last lap.
Countries have to pursue these efforts even as they reorient public health systems to face relatively new infections — like dengue — as well as challenges arising from the rise of lifestyle-related illnesses.
Also called non-communicable diseases (NCDs) or chronic diseases, these are not passed from person to person. The four main types are cardiovascular diseases (like heart attacks and stroke), cancers, chronic respiratory diseases (such as asthma), and diabetes.  Health planners call it a ‘double burden’ that many low — and middle — income countries have to face. Sri Lanka, whose overall health indicators are impressive for its level of income, has been grappling with this since the late 1990s. 
Rolling back infectious diseases
Worldwide, public health experts use a common set of definitions for phasing out infectious diseases. In their parlance:
- ‘Control’ means reducing the incidence and prevalence of a disease to a locally acceptable level;
- Elimination means reducing to zero of the incidence of disease in a defined geographical area (usually a country); and
- Eradication is the permanent reduction to zero of worldwide infections (as happened with smallpox in 1979).
“Microbes are dynamic and resilient: they spread locally, nationally and internationally with ease in our globalised world, and when they find susceptible populations they re-emerge as public health problems,” says David L Heymann, a professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine.
He wrote a decade ago: “Surveillance and continuation of control interventions are necessary to maintain achievements in infectious disease control unless transmission has been interrupted and the microbe destroyed worldwide.” 
This caution is illustrated by Sri Lanka’s experiences with malaria control in recent decades.
Thanks to indoor spraying and other measures since 1946, malaria cases came down from 91,990 in 1953 to a mere 17 in 1963. The island nation was hopeful of crushing the ancient scourge, but soon there was a resurgence: 538,000 cases were reported in 1969.
For the next 30 years, large numbers of cases were reported as the country struggled to maintain control efforts amidst a civil war in malaria endemic areas. 
Finally, they succeeded. From 1999 to 2011, the country’s Anti-Malaria Campaign (AMC) achieved a 99.9 per cent reduction in malaria (the war ended in 2009). There have been no deaths due to indigenous malaria since 2007, and no cases of indigenous malaria reported after October 2012.
In 2013, 2014 and 2015, the few reported cases (95, 49 and 36 respectively) all involved those who had contracted malaria while overseas (as migrant workers, business travellers or UN peacekeepers).
“As a result, the country has moved in to the phase of prevention of re-introduction of malaria,” says the AMC. 
Having completed three consecutive years without indigenous malaria, Sri Lanka recently applied for WHO certification as a malaria-free country.  That is expected before end 2016.
So far, 33 countries and territories have been certified and entered in the WHO register as having eliminated malaria through specific measures. In 2015, the Maldives was certified as malaria-free. 
But as long as the malaria-carrying mosquitos abound, countries cannot relax control measures.
“The price of an outstanding surveillance and response system, which is now essential, is not beyond the affordability of Sri Lanka’s health system, which is known to deliver an equitable and effective health service,” four public health researchers and officials wrote in a review article in 2014.
The authors added: “Singapore, with similar environmental risks for malaria as Sri Lanka, has sustained a malaria surveillance and response system to keep the country malaria-free, despite large volumes of labour migration into the country and small local outbreaks, which must reflect an assumption that the investments are well below the cost of a malaria resurgence.” 
Polio and Filariasis
Polio is another major disease whose roll-back is nearing the last lap. South Asia is the last stronghold of the crippling virus.
Polio cases worldwide have come down from an estimated 350,000 in 1988 (when WHO member states resolved to eradicate it) to 74 in 2015. Today, only two countries (Afghanistan and Pakistan) remain polio-endemic, compared to more than 125 in 1988. 
Thanks to a massive mobilisation, India succeeded in stopping polio transmission in January 2011. WHO’s South East Asia Region — home to a quarter of the world’s population — was certified as entirely polio-free in March 2014.
Polio work in Afghanistan and Pakistan (which fall under WHO’s Eastern Mediterranean Region) is held up by political instability. Violent attacks on vaccination workers have caused setbacks, as have widely held myths fuelling suspicions on vaccine safety. 
“As long as a single child remains infected, children in all countries are at risk of contracting polio. Failure to eradicate polio from these last remaining strongholds could result in as many as 200,000 new cases every year, within 10 years, all over the world,” cautions WHO. 
Meanwhile, progress against lymphatic filariasis (LF) has been more promising.
In June, WHO announced that the Maldives and Sri Lanka have eliminated LF, also known as elephantiasis. The mosquito-borne disease was crippling people for decades, forcing them to lead lives of stigma, discrimination and poverty.
“The success in the Maldives and Sri Lanka follows intensified mosquito control efforts; treatment of the infected population, disability prevention and control; strengthening of surveillance; and closely monitoring and evaluating these efforts which together helped eliminate LF as a public health problem,” WHO said. 
At a recent ceremony in Colombo to mark the accomplishment, the director of Sri Lankia’s Anti-Filariasis Campaign (AFC) highlighted the need for continuing disease surveillance in endemic areas while also conducting surveys in non-endemic areas. 
‘Ensure healthy lives and promoting well-being for all at all ages’ is one of the 17 Sustainable Development Goals (SDGs) adopted by all UN member states in September 2015. A multi-pronged strategy to deal with the double burden of disease is essential for pursuing this goal.
Nalaka Gunawardene is a Colombo-based science writer, blogger and development communication consultant. He tweets from @NalakaG.
This piece was produced by SciDev.Net’s South Asia desk.