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What are co-infections?

In simple terms, a co-infection is a simultaneous infection of an organism by two or more pathogen species. Co-infections are medically significant well beyond tick-borne diseases. In fact, a common co-infection among infectious diseases is that of HIV and Hepatitis C.

The term “Lyme disease co-infection” typically describes the type of case in which a patient is simultaneously infected with Lyme disease and one or more of any of the other tick-borne diseases that are commonly transmitted by the ticks that spread Lyme.

Lyme disease co-infections may be more common than single infections

So, how common are Lyme disease co-infections? Studies from the past several years indicate that tick-borne disease co-infections may actually be more common than single infections, though more research may change or deepen understandings of this issue.

In a 2017 survey, (LDo) profiled 3,000 chronic Lyme disease patients and found that over half of them reported laboratory-confirmed co-infections. 30% of those surveyed reported two or more co-infections.

Why are co-infections so prevalent? Part of the reason is that it is simply very common for a single tick to be carrying several different pathogen species. The LDo article above cites a study in France that found that every tick sampled carried at least one symbiont, or other microorganisms that can affect transmission of disease, and 45% were carrying up to five different pathogens.

With ticks able to carry so many pathogens and transmit them all in the same bite, it’s no surprise that co-infections may be “the rule, not the exception.”


The most common Lyme disease co-infections

According to LDo, the most common Lyme disease co-infections are reported in the following order from most to least common:

  1. Babesia: A parasite spread by ticks that causes a disease similar to malaria

  2. Bartonella: The bacteria that causes Cat Scratch Disease (also called cat scratch fever)

  3. Ehrlichia: A group of at least three sub-species that cause disease (Ehrlichiosis) in the U.S.

  4. Rickettsia rickettsii: The bacteria that causes Rocky Mountain Spotted Fever, the deadliest tick-borne disease in the world

  5. Anaplasma: A bacteria causing Anaplasmosis, with a sub-species in the U.S. and another in China

It is also possible to be co-infected with the potentially fatal Powassan virus. Finally, while more data is needed, it should be noted that there is one species of Borrelia that causes Tick-Borne Relapsing Fever – Borrelia miyamotoi – that is spread by blacklegged ticks, the same ticks that spread Lyme disease. As such, doctors who suspect a patient may be infected with Lyme disease should also consider testing for Tick-Borne Relapsing Fever.


Co-infections, diagnosis, and treatment

The presence of co-infections can significantly complicate the diagnostic process. Each co-infection needs to be tested for, diagnosed, and treated on its own. If you are diagnosed with and treated for Lyme disease but have a co-infection or multiple co-infections that were not detected because your doctor did not test for them, the Lyme treatment will not resolve the other infections. It is not uncommon for patients to undergo treatment for one tick-borne disease, only to have persistent symptoms related to a co-infection that was never diagnosed.

When testing for Lyme disease, it is crucial that physicians consider and test for possible co-infections. Untreated or undertreated tick-borne diseases can take a major toll on one’s health and finances, and in some cases – for example, with Rocky Mountain Spotted Fever or Powassan Virus – they can be deadly. Additionally, because pathogens can interact with each other within the human they’ve infected, there is evidence that co-infections can cause more severe symptoms and longer recovery periods.

Tick-borne disease co-infections

There is often a misunderstanding when people hear “Lyme Disease co-infections.” They assume that Lyme has to be present to be infected with any of the co-infections. This is not true. In fact, a more accurate description would be “tick-borne disease” co-infections. Therefore, it is possible to be infected with any one or more of the pathogens ticks carry. You could be infected with Babesia, for example, without getting Lyme, or contract TBRF Borrelia and Babesia, without Lyme.

Different Ticks

While this article focuses on the most common tick that carries Borrelia burgdorferi, the black-legged tick, it is important to keep in mind that there are many species of ticks and 

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