Everyone is familiar with the immunity created for many illnesses. Viruses like smallpox and chickenpox build an immunity with antibodies after a first infection.
But what about diseases that actually come back worse the second time?
Research on dengue fever, published in 2017, has people considering the idea with more evidence than before.
The dengue virus is broken up into four different branches, or “serotypes.” Many people may not realize that being infected with a serotype protects you from that specific one in the future, but not the rest.
The issue comes with the antibodies that helped defeat dengue the first time. These same antibodies can help a similar infection spread and grow the second time. This is called ADE, or antibody-dependent enhancement.
With ADE, antibodies recognize invading organisms that they believe to have seen before. The antibodies then latch onto the organisms so they cannot replicate and destroy cells. Though this might normally be an appropriate solution, with dengue it can lead to widespread attacks through macrophages.
Macrophages are cells which attempt to clean out the seemingly harmless bacteria by “eating” them. Instead, the virus reactivates inside and uses the macrophages to cause an even greater infection.
Zika resembles dengue in its Flavivirus makeup, meaning the same process applies to both viruses. If someone gets dengue and then Zika, for example, the experience with dengue can either mean a basic level of protection or a higher chance of infection.
Some diseases do not even rely on ADE to create this increasingly bad infection. Illnesses like malaria can use in a different, tag-team effect to produce a worse virus.
A 2013 report looked at this phenomenon in malaria. After contracting the two most common types of malaria, the parasites can work in succession to create a far worse attack with each infection. The parasite targets all red blood cells, regardless of age. Though it destroys millions of cells, the body can quickly replenish them.
But, as soon as more red blood cells return, they are exactly the type the second parasite needs – young. This can pose a greater risk to those infected since their cells are constantly attacked by two enemies instead of one.
Another strange relationship between viruses is that of chickenpox and shingles.
Chickenpox itself follows the usual rule where one infection leads to immunity. But, this doesn’t mean the virus simply disappears.
The varicella zoster virus which causes the pox stays dormant inside nerve roots. The virus can then develop into shingles later on in a person’s life. According to Time magazine, one-third of people are affected by shingles in their lives, usually after the age of 60.
The age of those dealing with shingles is important since it can be more difficult for people to fight as they get older. This less-responsive immune system is even the reason for different vaccines to treat the two viruses.
While many diseases get worse for a second infection, there’s is no one reason for this outcome.
There are different causes which lead to different effects on a case-by-case basis. Malaria may get worse due to the parasites which work together in succession. Chickenpox and shingles differ because of the virus that stays dormant to produce a harmful result later. With dengue fever and Zika, the answer comes with the antibodies.
In the end the main goal for travelers is avoiding general infection in the first place.
Have you had any experiences with diseases that were worse the second time? Do you still have any questions about dengue, malaria, Zika, chicken pox, or shingles? Let us know in the comments, or via Facebook and Twitter.
Written for Passport Health by Katherine Meikle. Katherine is a freelance writer and proud first-generation British-American living in Florida, where she was born and raised. She has a passion for travel and a love of writing, which go hand-in-hand.