A mysterious disease in Karachi?

The “mysterious disease” is behaving exactly like dengue minus the lab result

Recently the media is abuzz with news of a mysterious disease in Karachi. Many have asked me about it. Is this a new disease or a new virus? As reported, it has all signs and symptoms including decrease in platelets like dengue, but diagnostic tests are coming back negative. Karachi like other megacities is very susceptible to any new infectious disease. High population density, coupled with lack of clean drinking water and sanitation for masses, makes it super susceptible for any new or old infectious disease outbreak.

As US-CDC Resident Adviser of Field Epidemiology and Laboratory Training Program (FELTP), my teams of doctors from Sindh had investigated an outbreak of a new fungus in Karachi. Pakistan was the sixth country where this highly dangerous fungus was identified. We were the first one to do an epidemiological study to identify some of its risk factors. FELTP fellows from Sindh also investigated one of the largest outbreaks of “brain eating amoeba” and were able to interview families while some patients were still alive. Karachi also reported a “mysterious disease” affecting tens of thousands of patients some years back. Once FELTP fellows investigated the outbreak properly, it was indeed a new disease in Pakistan (chikungunya) but it had affected far fewer people. It was also expected in Pakistan as it is carried by the same mosquito which carries dengue. So environmentally and historically Karachi could initiate a new infectious disease but how to know if it’s a new disease or an old disease.

Many years back when I was in my medical college, one of our professors told us to “treat the patient and not the lab”. It means we need to pay attention to patient’s physical signs and symptoms more than what is coming back to us as laboratory results. Most people in Pakistan can’t afford expensive lab tests and good doctors pay attention to patients. In our days a favourite question in our oral exam of final year was to tell differential diagnosis. That means: which other disease could produce similar symptoms in patients? That is important for doctors to know so that they could exclude other diseases and treat the patient with proper medicines. When we can’t order a battery of lab tests, we start eliminating other diseases by first excluding the most common. If fever could be caused by mild flu but also present in many cancers, we need to first ensure that the patient does not have flu or any other common ailment. Once most common diseases are excluded only then physicians move toward investigating rare diseases.

According to reports the “mysterious disease” in Karachi is behaving exactly like dengue minus the lab result. NS1 which is the most common test for dengue has very high specificity of dengue meaning if it says you are positive then most likely this is a true report. However, it is not that sensitive means it could be false negative. Also, many dengue patients of today had dengue earlier by another type. Remember dengue has four viral types and infection with one gives you immunity from that type only. So you could still be infected by other types and secondary infection is more dangerous and increases chances of a false negative test.

It could be another disease too but until someone sitting in a lab identifies a new virus among patient samples, or a good epidemiological study tells us that it may be a new disease, stay focused on dengue. So, my advice to all is to keep yourself protected from mosquitoes by ensuring cleanliness in and around your house. Ensure windows have screens to keep mosquitoes off, wear long sleeves especially in morning and sunset and use mosquito repellents when going outside. Aedes aegypti (dengue mosquito) also spreads chikungunya, Zika fever, Mayaro, yellow fever viruses, and other diseases. So, a national comprehensive vector control policy implementation is needed. We finalised one back in 2019 and it may be laying in a closet in some ministerial office today.

Published in The Express Tribune, November 20^th, 2021.

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