In 2016, dengue hammered Krah. As many as 100 people living in this densely-packed, predominantly Muslim ghetto of about 1,000 families near Biharsharif contracted the disease, say residents. The scale of the outbreak was unprecedented. As Mohammad Ilyas, a young tailor who works and lives in Krah, said: “We never had such an outbreak earlier.”

The disease itself is a newcomer to the region. Krah and surrounding areas have been battered by many diseases. But many of the old diseases are in decline now, according to Dr Lakshmi Chaudhary who runs a clinic in adjacent Silao. “There were only two-three cases of jaundice last year,” he said. “Hepatitis B is even lower. We now almost never see cases of diarrhoea.”

Here, people now suffer from other ailments. There is more cancer, dengue and chikungunya, said Chaudhary.

This is the story across Bihar. Doctors, epidemiologists and people living across the state say that in the last ten years the state’s disease burden has seen three large changes. First, some infectious diseases like kala azar, measles, diphtheria, pertussis and polio that used to wreak havoc earlier are far less common now. Second, people are falling to new diseases like drug-resistant tuberculosis, dengue, chikungunya, Japanese encephalitis and arsenic poisoning. Third, some of the old infectious diseases – hepatitis A and E, malaria, pneumococcal meningitis and typhoid – are claiming more patients than before.

This is very different from the epidemiological transitions in other states. Dr T Sundararaman, who heads the School for Public Health at Mumbai’s Tata Institute of Social Studies pointed out that Kerala, for instance, moved from a burden of infectious diseases to chronic non-communicable ailments like diabetes, cancer and cardiac problems.

There are many interlinked factors responsible for the change in disease patterns in Bihar. The first of these is migration.

Vectors, pathogens and reservoirs

Like Ilyas, Dr Shakeel Ur Rahman remembers 2016 vividly. That year, six or seven out of every 100 patients he saw at his non-profit clinic in Patna had either dengue or chikungunya. Between August and September, he got 2,000 patients ailing from one of the two diseases. “Five years ago, we never got these diseases,” he said.

Poor water drainage and garbage disposal in patna, no more than two kilometres from the patna train station. (Photo: M Rajshekhar)

Despite these observations by doctors in the state, the question of when these diseases reached Bihar is not easy to answer and that is partly because Bihar has very poor disease surveillance. What is easier to understand is how the diseases have got here.

The first epidemic of a clinical dengue-like illness was recorded in Madras as far back as 1780, according to a paper titled Dengue In India, published in the Indian Journal Of Medical Research in September, 2012. After that, the country saw periodic, isolated outbreaks of dengue. But the disease began to crop up on the public health radar only in the late nineties as outbreaks became more frequent and widespread. The paper says: “The first major wide spread (sic) epidemics of dengue occurred in India in 1996 involving areas around Delhi and Lucknow and then it spread to all over the country.”

To spread, infectious diseases need a confluence of three factors – the pathogen, a vector and a mathematical tipping point called “man hour density”.

The dengue virus’ vector is Aedes aegypti, a mosquito with a distinctive striped abdomen.

Man hour density refers to the concentration of pathogens needed in a body to overwhelm the body’s defences. The pathogen load needed to overwhelm the body’s defences varies from disease to disease. Take filaria, for example, which spreads through the bites of the female culex mosquito. A patient needs more than 500 bites before the disease manifests, said a medical researcher in Bhagalpur who did not want to be named. These bites, he said, can be accumulated over 3-4 years.

Pradeep Das, the director of Patna’s Rajendra Memorial Research Institute of Medical Sciences, said: “A person needs to be bitten just six times [by a sand fly] to contract kala azar.”

The dengue trifecta

Bihar has plenty of Aedes aegypti. “It’s an aggressive mosquito,” says Manju Rahi, an epidemiologist working on vector-borne diseases at the Indian Council for Medical Research’s tightly packed office in Delhi. “In a single blood meal, it can infect 8-9 people. Which is why you get cases of multiple people in one family contracting dengue.” In recent years, its numbers might have increased due to a number of factors. Warmer winters may have extended the months during which the mosquito remains active. Even Bihar’s attack on sand flies as the state tries to eradicate kala azar might have resulted in the mosquitos taking over the sand flies’ ecological niche. As Das said: “With vector-borne diseases, one vector reduces in numbers, another comes in.”

For a dengue infection to spread, many Aedes aegypti mosquitoes need to carry the dengue virus. The mosquitoes pick up the virus when they bite people who are infected or are carriers. People who carry the pathogen but do not contract the illness, either because of they have strong immunity or because the pathogen load is low, are called reservoirs.

“The greater the number of reservoirs in a population, the greater the probability the vector will carry that pathogen,” said Das.

And then, migration and the constant movement of people in and out of the state has helped bring in more of the pathogen. Many labourers from Bihar work in cities like Delhi that have been badly affected by dengue. Said Ilyas about Krah: “Delhi, Surat, Jaipur... koi bhi state chuta nahin hain.” There is no state where our people are not working.

Many of these workers live in conditions where the Aedes aegypti mosquito flourishes. They are often underpaid and needing to send money home and so do not eat well leaving them more vulnerable than others to disease. Moreover, many Biharis travel home for Chhatt Puja, which falls at the height of the dengue season.

“People who go to Delhi and elsewhere come back with it,” said Das. “Our first infection of dengue this year came from Bangalore. That person, a student, got the illness there and came back.”

The combination of new loads of the pathogen coming in, the vector already present in large numbers and a large population of people who are reservoirs for the virus makes an outbreak almost inevitable. According to Ragini Mishra, lead epidemiologist at the central government’s Integrated Disease Surveillance Programme’s office in Bihar, Aedes aegypti numbers drop in the winter but they they do not fully die out. The dengue virus also goes into a shutdown mode but does not die out either. Once humidity and temperature rise, it starts multiplying inside mosquito again.

The sanitation problem

Reservoirs – the people who carry the dengue virus who do not show symptoms of the disease – are usually found in the most vulnerable communities, said the researcher in Bhagalpur.

“Women and children, scheduled castes and tribes,” he elaborated. “Given the conditions they live in – poor access to water, low quality housing, poor sanitation – they have a predisposition for communicable ailments.”

This predisposition of vulnerable communities to having more reservoirs and more infections is partly physical and partly financial. Poverty often leads to malnourishment, which impairs immunity. Poverty also makes people live in conditions with high exposure to disease vectors and pathogens.

Krah illustrates just that. No more than a kilometre from the tiny town of Silao and about 12 kilometres from Biharsharif, Krah is a poorly-built, filthy place. Plastic waste lies everywhere – on the ground and in clogged drains. Most of its houses are single-storeyed structures with unplastered walls. These houses, Ilyas said, have come up haphazardly. There is little space between houses. Some have come up on low-lying land. Consequently, in the monsoons, rainwater has nowhere to drain and shallow ponds form amidst houses till after the rains stop when evaporation dries them out.

In Bettiah and across Bihar, houses have come up in low lying areas. (Photo: M Rajshekhar)

Shafiq Alam is a young man who postponed his evening prayers at the mosque to give this reporter a tour of Krah. Near a house we pass, dirty water is flowing out of a pipe into a stagnant puddle. Like the ponds, said this water too vanishes through only when the sun dries it out or when it soaks into the soil. Animals – cattle, ducks, hens, goats – are rooting through this water. There is no garbage disposal or drainage, said Alam.

At another house, a middle-aged couple is making beedis – a common source of employment here. It is a low paying job. It will take one person 12 hours to roll thousand beedis and rolling 1,000 beedis nets him Rs 100.

A couple making beedis at their house in Krah. (Photo: M Rajshekhar)

Krah was not always this densely-packed. It was a village, bounded on one side by a pond and fields everywhere elsewhere. Things began to change, Ilyas said, after 1982 when this part of Bihar saw communal violence. Local Muslims began clustering in Krah for safety, houses came up wherever there was land. Today, the original village with its old houses and painted walls is only visible from deep in the ghetto as one walks towards the pond and the train track.

A small group of men in neighbouring Silao that has a majority of upper caste Hindus called Bhumihars blamed Krah’s dengue outbreak on the Muslims saying, “People, animals, all live together. There is filth everywhere.”

But garbage and a lack of sanitation extends well beyond this area. Krah’s losing battle with hygiene and planning is more like the norm in the whole state of Bihar rather than an exception. Skewed landholding practices and the absence of industry is forcing people to leave Bihar’s villages for its cities. Most of them end up living in slums in the cities, said Dr Ashok Ghosh, head of research at Mahavir Cancer Hospital, a charitable medical institution. “Those are very poor living conditions, very unhygienic,” he said. “The pipes for sanitation are old. The ones for water are broken.”

Even in Silao, one had to just look past where that group of men in Silao was sitting to see plastic waste and pools of stagnant water.

Poverty, overcrowding and poor planning creates optimal conditions for all vector-borne diseases, said Rahi. Stagnant water attracts Anopheles culex, the vector for diseases like malaria. Erratic water supply results in families stocking water at home, which is perfect for Aedes aegypti to breed in. Even rainwater that collects in plastic waste can house mosquito eggs. “Even the discarded cap of a water bottle is enough,” said Rahi.

Mishra, the epidemiologist in Patna, said that dengue was first considered an urban disease because of the problems of sanitation. But now, as urbanisation gathers pace, her team is seeing dengue outbreaks even in peri-urban areas.

Even as Krah’s population grew, civic amenities did not keep pace. According to Alam, no vehicle comes to collect garbage from here. Local cleaners come to the area occasionally but only sweep the main street and dump the waste in the pond or on its banks. The adjacent pond has plastic bags and cups clinging to its banks.

Through migration, poor urban planning, poverty, the growth of slums, malnourishment and social discrimination the entirely modern disease of dengue has found a home in Bihar.

The next article in this series will look at Bihar’s efforts to fight dengue.

This reporting project has been made possible partly by funding from New Venture Fund for Communications.