MUMBAI, INDIA — Even as a deadly second wave of Covid-19 ravages India, doctors are now reporting a rash of cases involving a rare fungal infection — also called the "black fungus" — among recovering and recovered Covid-19 patients.

The infection has a very high mortality rate and treatment often involves the removal of an eye. Here are the details:

The BBC reports that surgeons in India are reporting a sharp increase in the number of mucormycosis cases in patients who survived Covid-19.

Mucormycosis is a rare fungal infection that is caused by exposure to mucor mould; which is commonly found in soil, plants, and even in the mucus of healthy people.

It affects the sinuses, the brain and the lungs, and can be life-threatening in diabetics or people with weakened immune systems.

The infection has a frightening mortality rate of 50%, and often requires the removal of an eye or sinus tissues.

Diabetics who survived coronavirus are especially at risk. Some doctors believe that's because diabetes lowers the body's immune defences, then coronavirus exacerbates the problem, and then steroids — which help fight coronavirus — acts like fuel to the fire.

Steroids reduce inflammation in the lungs for Covid-19 and limit the damage. But they also reduce immunity in both diabetic and non-diabetic Covid-19 patients.

It is thought that this drop in immunity could be triggering India's spike in mucormycosis cases.

Mumbai's busy Sion Hospital has reported 24 cases of the fungal infection in the past two months — up from six cases a year.

Eleven of them had to lose an eye, and six of them died.

Most of the patients are middle-aged diabetics who were struck down by the fungus two weeks after recovering from Covid-19.