Infectious diseases and their complications

Is COVID-19 unique in causing so many health impacts? What can we do?

Hello friends! It’s been awhile since my last edition, but I did tell you from the start that my newsletters were likely to be at most once a month for awhile. The end of the spring semester is approaching though, so I hope to be able to tackle some more topics soon!

In today’s edition I wanted to cover another topic I mention often in my microbiology class, and that is sequelae.

In microbiology, sequelae refers to the health complications that can arise following infection with a pathogen.

One of the most common questions people ask me over on Instagram is whether or not COVID-19 is unique in terms of the risk of sequelae, known as long COVID or post acute sequelae of COVID-19 (PASC). I’ve covered this is varying degrees but wanted to put this information together in one place.

So, is post infection sequela unique to COVID-19? The answer is no, but there is some uncertainty due to lack of data.

However, there is a lot of uncertainty on this topic in general. This uncertainty exists because not much research funding has been put into understanding the long term consequences of infectious disease. However, this is something that needs to change. Below we will cover why, as well as go over some examples of other infections that cause sequelae.

Climate Change and Emerging Pathogens

Climate change is a problem for many reasons, but one reason relates to its impact on emerging pathogens. As the climate shifts, the risk is increasing that we will encounter never before seen pathogens, or pathogens we haven’t seen in centuries. As the climate changes we are likely to enter a period of history where infectious disease pose more of a threat. This means not only should we pour more funding into climate change, but also into the infrastructure to prevent and deal with emerging pathogens and pandemic preparations.

An important part of this, is also understanding that infectious diseases can cause long term consequences even if the person survives the infection. Understanding how to prevent infection is key, but so is understanding why sequelae happens, who is at risk, and methods to prevent and treat these issues.

Examples of Post Infectious Sequelae

Epstein-barr virus (EBV)

EBV is the virus that causes a disease commonly known as mononucleosis. EBV is an interesting virus. When children are infected many are asymptomatic or have mild cold symptoms. However, when a teen or adult is infected the symptoms are much more severe and usually present as mononucleosis.

Once patients recover from the initial EBV symptoms the virus lies latent (which means dormant) in your body forever, and under some conditions may reactivate.

After these initial symptoms pass, it is also well documented that complications can occur. New data shows a strong association between EBV and the development of multiple sclerosis. Other data shows increase risk of developing lymphoma and related cancers, brain inflammation, and other autoimmune diseases. There is also an area of active debate and research that is looking at the potential link between EBV and the development of myalgic encephalomyelitis (ME).

Measles

Measles is caused by the virus Measles morbillivirus. This virus is highly contagious, but cases are low in many parts of the world thanks to the development of a vaccine for measles (it is a part of the MMR vaccine).

Those who get measles can develop issues such as deafness or blindness. Central nervous system issues can also occur such as acute post-infectious measles encephalomyelitis which has a 20% mortality rate, and is associated with other complications such as seizures.

Another complication is Subacute Sclerosing Panencephalitis. Children and young adults with this condition typically report a measles infection as a young child, and then symptoms begins 6-8 years later. This is a neurological condition where symptoms begin slowly and then can progress and result in paralysis and comas.

We now also know that measles can induce what is called immune amnesia, where having a measles infection replaces all your immune memory cells. Effectively erasing the immune memory you’ve made to prior pathogen or vaccination exposures. Note, this is NOT seen with the measles vaccine.

Influenza

Influenza is a respiratory pathogen that has been causing infections and complications for centuries. For example, history books note many individuals suffering from fatigue and neurological issues following “Russian influenza” in the 1890’s. Neurological issues like seizures, have also been noted following the 1918 flu pandemic.

The influenza strains circulating in 2009 have been associated with altered mental states and neurological impacts in children.

In 2013 a new strain of influenza known as H7N9 infected humans. Some of those who recovered had lung injury and psychological impairment.

Respiratory Syncytial Virus (RSV)

RSV bronchiolitis has been associated with respiratory related sequela and is estimated to increase the risk 2-12x of a child developing asthma compared to a child without this history.

Strep Throat

Strep throat is a bacterial infection caused by bacteria in the family of group A streptococcus. One of the reasons is it advisable to treat strep throat is due to some of the longer term issues that can arise due to these infections such a rheumatic fever (RF). RF is an autoimmune disease triggered by a strep infection that can impact the heart and other parts of the body. Importantly, these complications have decreased thanks to the proper use of antibiotics in treating bacterial infections.

Mumps

Mumps is caused by the virus Mumps orthorubulavirus. Thanks to the mumps vaccine (it is also part of the MMR vaccine), is it no longer a common virus we think about. However, when it was common we noted sequela that included deafness and decreased fertility (timeline of how long this lasts is unclear).

Polio

Polio virus is known to cause post-polio syndrome (PPS) that can impact people decades after their original polio infection. Symptoms include fatigue, muscle weakness, shrinking of muscles, muscle and joint pain, difficulty walking and potentially trouble breathing.

How common are post-infectious sequelae related conditions?

It is unclear! Long COVID is estimated to impact about 20% of the population infected with COVID-19, but this percentage can vary greatly depending on which study you look at. This wide range is due to the fact that each study is looking at different ages, populations and is defining long COVID slightly differently. This makes it challenging to get more precise measurements.

In terms of other post-infectious sequelae you can find ranges reported, but it is also likely information is being under reported. It can be hard to associate complications with an infectious disease outside of a pandemic. This is because it can be easier to see associations when multiple people are getting infected simultaneously.

However, to give you a frame of comparison:

Post polio syndrome is estimated to impact about 25-40% of patients who survive polio infection.

Up to 2.5 million people in the USA may have ME linked to an infectious disease (though more research is needed).

In the case of measles, it is estimated about 0.1% of those infected will develop acute post infectious measles encephalitis and 4-11/100,000 will develop subacute sclerosing panencephalitis.

What should I do with this information?

I am NOT sharing this information to terrify you. Instead, I am sharing in hopes of informing you, and helping to increase awareness of the fact that pathogens are not our friend. Yes, they are currently a part of our existence, but that does NOT mean we do nothing to prevent future outbreaks and pandemics.

It is difficult to live with uncertainty, and there is still a lot of uncertainty about long COVID and other post infection sequelae. However, there are a lot of things we can do.

• We can do things to avoid infectious diseases. These include hand washing, masking, vaccinations, staying home when sick, etc…

• We can encourage funding into research about what causes post-infectious sequelae.

• We can put more time, research and money into stopping the next pandemic.

• We can bolster public health and public services.

• Improve ventilation and filtration in public spaces, which decrease the spread of infectious disease.

• Fund research into designing universal vaccines for things like influenza.

• Fund research and development of therapies for those suffering from ME, long COVID and other post infectious complications.

These things require the support of governments, which means we can make a difference by calling our representatives and voting for people who will support these types of measures.

At the end of the day, pathogens do not respect borders. This is a global problem, and addressing it collectively will make us all healthier in the long run.

So no, COVID-19 is not unique in causing complications, whether or not it causes them more frequently than other infectious is unclear due to lack of data.

However, the take home should be that we all should be striving to improve public health, pandemic preparedness and infrastructure to mitigate the spread of infectious disease and their complications.