Lyme Disease Co-infections

Quick answer

Lyme disease co-infections are other tickborne infections caught along with Lyme, usually from the same blacklegged tick. The main ones are babesiosis and anaplasmosis; Borrelia miyamotoi, Powassan virus and one form of ehrlichiosis are also possible. Most people with Lyme do not have a co-infection, but a high fever, abnormal blood counts or no improvement on treatment are reasons to ask.

What is a co-infection?

A co-infection means you have two or more infections at the same time. With ticks, this can happen because a single tick may have picked up more than one germ while feeding on infected animals. For example, CDC notes that Babesia microti usually infects white-footed mice and other small mammals.

The blacklegged (deer) tick is the main concern because it spreads Lyme disease in the East and Midwest and can carry several other germs too. On the Pacific coast, the western blacklegged tick plays a similar role for some of them. Learn more on our blacklegged tick and ticks that carry Lyme disease pages.

Timing matters, and it may differ by germ. A lab study cited by CDC (MMWR, 2017) found Powassan virus passed from ticks to mice within 15 minutes; CDC gives no minimum attachment time for people. That is one more reason to check for ticks daily and remove them quickly. See how long a tick needs to be attached.

How common are co-infections?

Exact numbers vary by place and year, and good data are limited. Here is what the sources we checked actually say:

• Anaplasmosis. A CDC page for health care providers states that co-infection of Anaplasma with non-rickettsial germs (such as the Lyme bacterium) has been reported in fewer than 10% of patients.
• Early Lyme disease in New York. A study published in CDC’s journal Emerging Infectious Diseases (2019) tested 52 adults with an erythema migrans rash in New York’s Lower Hudson Valley. Nearly 90% showed no evidence of co-infection. Four people (about 8%) had convincing evidence of babesiosis, and up to six may have had it. None met the criteria for anaplasmosis, B. miyamotoi or Powassan virus. The authors note the study was small and from one region.

We don’t rank co-infections from most to least common, because the sources we checked don’t do that for the whole country. Your own risk depends on where you live and travel.

Lyme co-infections chart

This chart summarizes CDC information on each infection. It is a starting point for a conversation with your provider, not a way to diagnose yourself. Tap a name to jump to it, or open the full guide.

Spotted fevers and alpha-gal are spread mainly by ticks that do not carry Lyme disease, so they are not classic same-bite co-infections. We include them because their early symptoms can overlap with other tickborne illnesses and because people in some areas are exposed to several kinds of ticks. See types of ticks.

What about Bartonella?

Many patient groups talk about Bartonella as a Lyme co-infection. The official picture is different, and we want to be clear about it:

• CDC’s position: CDC does not list Bartonella as a tickborne disease. Its Bartonella page says there is no evidence that these bacteria spread to people through tick bites. CDC also mentions one lab study that found transfer from ticks to animals and says more research is needed to know whether this happens in nature.
• The debate: A 2010 review in Emerging Infectious Diseases looked at the case for tick spread. Bartonella DNA has been found in many tick species, and there are case reports of illness after tick bites. But the authors concluded the evidence was not yet sufficient: finding DNA doesn’t prove the bacteria are alive or can infect, human cases often had other exposures such as cats, and no experiment had shown a tick passing Bartonella to an animal by biting it.

So tick transmission remains unproven. If you have symptoms and possible exposures, including cats or fleas, your provider can weigh that. Read more on our Bartonella page.

When to suspect a co-infection

These are the clues named by the IDSA/AAN/ACR guideline and CDC. They are reasons to talk with your provider, not proof of a co-infection:

• A high fever with Lyme disease, or a fever that lasts more than a day once Lyme treatment has started.
• Fever that continues despite doxycycline. The guideline says babesiosis is an important consideration here. Babesiosis is caused by a parasite and needs different medicines.
• Abnormal blood counts. Low platelets, low white cells and anemia can occur in both anaplasmosis and babesiosis. Signs that red blood cells are breaking down (such as anemia with raised bilirubin or LDH) point especially toward babesiosis, according to the guideline.
• A rash with an illness that looks like anaplasmosis. CDC notes that rash is uncommon in anaplasmosis, so a rash may suggest co-infection with Lyme or another tickborne disease.
• Not improving as expected. For anaplasmosis and ehrlichiosis, CDC says fever usually improves within 24 to 48 hours of doxycycline, and a lack of response suggests the illness may be something else.

Doxycycline, a common Lyme antibiotic, is also the CDC-recommended treatment for anaplasmosis and ehrlichiosis. The guideline says suspected co-infection with Anaplasma or E. muris eauclairensis would call for doxycycline. It does not treat babesiosis or viruses like Powassan.

Testing questions to ask your provider

There is no single test for “co-infections.” Each germ has its own tests, and timing matters. These questions can help you have a focused conversation. Take them to your appointment along with our doctor visit checklist.

1. Given where I live and traveled, which tickborne infections are possible? Tell your provider about tick bites, time in wooded or brushy areas, and trips. CDC notes many people never notice the bite.
2. Should I have a complete blood count and liver tests? CDC and the guideline describe blood count and liver changes as clues for anaplasmosis, ehrlichiosis and babesiosis.
3. Would a manual blood smear for Babesia make sense? CDC advises clinicians to specifically request a manual (not automated) smear review, and more than one may be needed.
4. Is it early enough for a PCR test? For anaplasmosis and ehrlichiosis, CDC says PCR on blood works best in the first week and becomes less sensitive soon after antibiotics start.
5. Do I need a second antibody test later? For anaplasmosis and ehrlichiosis, CDC says the best evidence is a rise in antibodies between a sample taken early and one taken 2 to 10 weeks later. A single early test can be negative.
6. Should treatment start before results come back? For anaplasmosis, ehrlichiosis and spotted fevers, CDC says treatment should not be delayed while waiting for results.
7. Could another infection affect my Lyme test? CDC notes relapsing-fever infections, such as B. miyamotoi, can cause false-positive Lyme antibody tests. See our Lyme disease test guide.

Preventing co-infections

CDC notes there are no vaccines for anaplasmosis, ehrlichiosis, Powassan virus or Rocky Mountain spotted fever, so the best protection is avoiding tick bites. CDC’s core advice is similar across these infections: use tick repellent in tick habitat, wear long sleeves and pants, check yourself, your children and your pets after being outdoors, and remove attached ticks promptly. Our Lyme disease prevention guide walks through the steps.

CDC’s anaplasmosis and ehrlichiosis guidance says to see a provider if fever, rash, headache or other symptoms develop within two weeks of a tick bite. Some infections, like babesiosis, can take weeks or months to show up, so mention any bite even later. This is part of step 3 of our plan: recognize the signs.

Frequently asked questions