New Delhi, Jan 18 (IANS): A fatal lung disease that begins with dry cough, causes breathing difficulty, and worsens over years may have played a significant role in the deaths caused by Covid-19 infections, according to a scientist duo.

Much like cancer, the disease called interstitial lung disease (ILD), goes undetected for years.

As the disease progresses, the lung shrinks, making it difficult for the patient to breathe.

India has an incidence rate of 10 to 20 cases per 100,000 in the population related to industries and lung diseases.

"The interstitium is the connective tissue between two sacs or the region that links alveoli together in the lungs. When this interstitium thickens, it constricts the air sacs, reducing lung size. This constriction leads to a decrease in airway size, resulting in a significant reduction in the overall oxygen intake. This condition, known as restriction, involves compression due to the shrinking of connective tissue between the lung alveoli," Dr Asmita Mehta, Professor and HoD of Respiratory Medicine at Amrita Hospital Kochi, told IANS.

What makes the disease fatal is the late diagnosis, said the distinguished pulmonologist.

"By the time the patient will come to us, it will be too late because the diagnosis of ILD happens very late. ILD starts with a very, very minor symptom, dry cough and breathing difficulty, which progresses over years. Just like cancer, the diagnosis of ILD is also delayed," she said.

Professor Athol Wells, associated with Royal Brompton Hospital in London and Imperial College London, said that the average survival is three to four years after diagnosis. It is because of the tremendous delay between the time of starting symptoms and the diagnosis made.

"It is a fatal disease with a very bad quality of life and significant morbidity," the Professor told IANS.

Covid-19 infection is known to cause fibrosis (scarring) in the lungs. While the condition reversed in some people and they returned to their pre-Covid status, however, in some there was no reversal and the infection turned fatal.

This could have been due to pre-existing ILD, the scientists said.

"There is a fibrosis which causes scarring that will be irreversible. So those people who developed severe Covid, developed almost respiratory failure to the extent that they were on ventilator support for 15-20 days,” Mehta said.

"I strongly doubt that they were already having some coexisting ILD before they developed Covid and then went on ventilator. They could not go back to that normal level.

"I always had a doubt that they might have an already coexisting disease, which was not diagnosed before Covid. In another set of people, we saw total reversal of lung fibrosis," she said.

The experts noted that people who already had diseased lungs due to ILD and if they developed Covid, they had more chances for need of ventilation, ICU care and a worse prognosis. They also had a prolonged recovery time and long Covid syndrome.

"I have no doubts that if you have interstitial lung disease before you get Covid, you are at much higher risk of dying of Covid because you are starting with the loss of your lung reserve in the first place," Wells said.

"Abnormalities that are there beforehand might not have declared themselves clinically. Because together with Covid it may have caused damage to your immune system," he said, adding that the disease may also likely worsen long Covid.

While there are about 200 types of ILD, if a person is diagnosed at the juncture of lung inflammation, the disease can be cured. But it "tends to be overlooked" and the coughs get treated for asthma, or other lung disorders.

Further, Mehta said that it also becomes hard to explain the disease to the patients, "because unlike cancer it is not much understood, and not much publicised disease, but it is increasing in India".

The scientists told IANS that pollution, and smoking are major reasons for the disease, but many are also autoimmune in nature that are majorly genetic.

Mehta said people with excreta exposure like farmers or those who indulge in rubber tapping in Kerala, or those exposed to particular fungi in Kerala also have some kind of ILD. The scientists urged the need to sensitise doctors to diagnose ILD early, and not to look at coughing and breathing problems among people as only cases of asthma, COPD, or tuberculosis.