Lyme Disease Co-Infections: Symptoms, Testing, and Treatment

Lyme disease co-infections occur when a tick transmits more than one infectious pathogen during a single bite. Black-legged ticks can carry bacteria, parasites, and viruses capable of infecting humans at the same time.

Today, ticks harbor multiple infectious pathogens that can be transmitted through a tick bite or occasionally through contaminated blood transfusions. The Centers for Disease Control and Prevention (CDC) reports that “a single tick can transmit multiple pathogens, including bacteria, viruses, and parasites.” [1]

When this occurs, patients may develop Lyme disease together with additional tick-borne infections, commonly referred to as Lyme disease co-infections.

Lyme disease co-infections matter because they may make patients sicker, prolong illness, and require different treatment than Lyme disease alone.

Between 2004 and 2016 alone, the CDC identified seven new tick-borne microbes capable of infecting humans. [1]

Common Symptoms of Lyme Disease Co-Infections

Lyme disease co-infections may cause symptoms that are more severe, prolonged, or different from Lyme disease alone.

Depending on the organism involved, symptoms may include:

• High fevers or chills
• Drenching sweats
• Severe fatigue
• Headaches
• Shortness of breath
• Neurologic symptoms
• Psychiatric symptoms
• Swollen glands
• Muscle and joint pain

Some patients develop symptoms that do not follow the typical pattern of Lyme disease, raising suspicion for additional infections.

Ticks Harbor Multiple Pathogens

Studies show that many ticks carry more than one disease-causing organism.

In one investigation conducted in Suffolk County, Long Island, more than half (67%) of ticks carried at least one pathogen. The Lyme disease bacterium Borrelia burgdorferi was the most prevalent (57% in adult ticks and 27% in nymphs), followed by Babesia microti (14% in adults and 15% in nymphs).

Another study found that co-infection occurs in up to 28% of black-legged ticks in Lyme endemic areas of the United States.

Researchers have also reported that among infected ticks, nearly 45% carried multiple pathogens — sometimes as many as five different microbes.

Lyme Disease With Co-Infections

Researchers from Columbia University, Tufts Medical Center, and Yale School of Medicine examined the frequency of co-infections in patients diagnosed with Lyme disease.

• 40% of Lyme disease patients had concurrent Babesia
• 1 in 3 patients with Babesia also had Anaplasmosis
• Two-thirds of patients with Babesiosis had concurrent Lyme disease

Why Lyme Disease Co-Infections Are Often Missed

Co-infections are often overlooked for several reasons:

• Symptoms overlap with Lyme disease
• Testing is limited or insensitive
• Many patients are not routinely evaluated for additional tick-borne infections
• Some infections require specialized laboratory testing

One study found that among nearly 3 million tick-borne disease specimens, only 17% were tested for infections other than Lyme disease.

This means many co-infections may go undiagnosed.

Most Common Lyme Disease Co-Infections

The most frequently recognized tick-borne co-infections include:

• Babesia
• Anaplasmosis
• Ehrlichia
• Bartonella
• Southern Tick-Associated Rash Illness (STARI)
• Borrelia miyamotoi

Babesia

Babesia is a parasite that infects red blood cells. It is transmitted primarily by ticks but can also be spread through blood transfusions.

Symptoms often include fever, chills, sweats, fatigue, headaches, and shortness of breath.

Co-infection with Babesia may increase the severity and duration of Lyme disease symptoms.

Anaplasmosis

Anaplasmosis is caused by the bacterium Anaplasma phagocytophilum and is transmitted by the black-legged tick.

Symptoms typically include fever, headache, fatigue, and muscle aches. While most infections are mild, some patients require hospitalization.

Bartonella

Bartonella species are associated with cat scratch disease but have also been detected in ticks.

Symptoms may include fever, fatigue, swollen lymph nodes, neurologic symptoms, and psychiatric manifestations in some patients.

STARI (Southern Tick-Associated Rash Illness)

STARI is an emerging tick-borne illness resembling Lyme disease and occurring primarily in the southeastern United States.

The long-term consequences and optimal treatment remain uncertain.

Borrelia miyamotoi

Borrelia miyamotoi causes a relapsing fever-like illness transmitted by the same ticks that spread Lyme disease.

Patients typically present with fever, headache, fatigue, and muscle aches but often do not develop a rash.

Clinical Takeaway

Tick-borne co-infections are increasingly recognized in patients with Lyme disease.

When patients present with unusually severe symptoms, persistent illness, or poor response to standard Lyme disease treatment, clinicians should consider the possibility of co-infections.

These infections may complicate diagnosis and require different treatment strategies.

Frequently Asked Questions

Can you have Lyme disease and Babesia at the same time?

Yes. Babesia is one of the most common Lyme disease co-infections and may worsen symptoms or prolong illness.

Do Lyme disease co-infections require different treatment?

Yes. Some co-infections such as Babesia require treatment different from standard Lyme disease antibiotics.

Why are Lyme disease co-infections often missed?

Symptoms overlap with Lyme disease, testing is limited, and many patients are not routinely evaluated for additional tick-borne infections.

Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention