Scientists recognize more than a dozen tickborne diseases in the United States and new ones are still being discovered. One tick may carry more than one disease, so sometimes people get more than one co-infection from the bite of a single tick. The symptoms of these coinfections are often nonspecific – such as fever and headache – which makes diagnosis difficult. And the treatments may be different. Doxycycline, for example, works for Lyme disease and ehrlichiosis, but is not effective for babesiosis.
Experienced doctors may be able to distinguish each of the tick-borne coinfections and order appropriate tests and treatment. Sometimes they start to suspect a coinfection when the patient doesn’t respond well to treatment and it becomes obvious that something else is causing the symptoms. Coinfection generally results in more severe illness, more symptoms, and a longer recovery.
Babesiosis is an infection caused by a malaria-like parasite, also called a “piroplasm,” that infects red blood cells. Babesia microti is believed to be the most common piroplasm infecting humans, but scientists have identified over twenty piroplasms carried by ticks. Ticks may carry only Babesia or they may be infected with both Babesia and Lyme spirochetes. People can also get babesiosis from a contaminated blood transfusion.
The first case of babesiosis was reported from Nantucket Island, Massachusetts, in 1969. Since the late1980’s, the disease has spread from the islands off the New England coast to the mainland. Cases have also been reported all across the United States, Europe, and Asia.
Symptoms of babesiosis are similar to those of Lyme disease but it more often starts with a high fever and chills. As the infection progresses, patients may develop fatigue, headache, drenching sweats, muscle aches, nausea, and vomiting. Babesiosis is often so mild it is not noticed but can be life-threatening to people with no spleen, the elderly, and people with weak immune systems. Complications include very low blood pressure, liver problems, severe hemolytic anemia (a breakdown of red blood cells), and kidney failure.
Blood smears may be examined under a microscope to try to identify the parasite inside red blood cells, however this method is reliable only in the first two weeks of the infection. Commercial tests currently work for only three species of Babesia, and there are likely many species yet to be discovered. The PCR (polymerase chain reaction) test can detect babesia DNA in the blood. The FISH (Fluorescent In-Situ Hybridization) assay can detect the ribosomal RNA of Babesia in thin blood smears. The patient’s blood can also be tested for antibodies to Babesia. It may be necessary to run several different tests and negative results should not be used to rule out treatment.
Babesiosis is treated with a combination of two types of anti-parasite drugs, atovaquone (Mepron, Malarone) plus an erythromycin-type drug (azithromycin, clarithromycin, or telithromycin). Long-standing infections may need to be treated for several months, and relapses sometimes occur and must be retreated.
Bartonella are bacteria that live inside cells; they can infect humans, mammals, and a wide range of wild animals. Not all Bartonella species cause disease in humans. Bartonella henselae causes an important emerging infection first reported in 1990 and described as a new species in 1992. It is mainly carried by cats and causes cat-scratch disease, endocarditis, and several other serious diseases in humans.
Bartonella bacteria are known to be carried by fleas, body lice and ticks. Scientists suspect that ticks are a source of infection in some human cases of bartonellosis. People with tick bites and no known exposure to cats have acquired the disease. People who recall being bitten by ticks have been co-infected with Lyme and Bartonella. More research needs to be done to establish the role of ticks in spreading the disease.
Scientists have identified several species of Bartonella. One is carried by sand flies in the Andes Mountains in Peru, Columbia, and Ecuador. Another is found worldwide in human body lice. Bartonella bacteria have been found in the European sheep tick. Five different Bartonella species have been detected in 19.2% of I. pacificus ticks collected in California.
Bartonellosis is often mild but in serious cases it can affect the whole body. Early signs are fever, fatigue, headache, poor appetite, and an unusual, streaked rash. Swollen glands are typical, especially around the head, neck and arms. Burrascano suspects bartonellosis when neurologic symptoms are out of proportion to the other systemic symptoms of chronic Lyme. He also notes gastritis, lower abdominal pain, sore soles, and tender subcutaneous nodules along the extremities. Lymph nodes may be enlarged and the throat can be sore.
Polymerase chain reaction (PCR) and tissue biopsy can be used, however they are also insensitive, as are standard blood tests.
Erythromycin and doxycycline have been used successfully for standard Bartonella, but Burrascano suspects that tick-borne Bartonella is different and recommends levofloxacin or, for children under 18, azithromycin.ks.
There are two kinds of ehrlichiosis, both of which are caused by tick-borne rickettsial parasites called Ehrlichia that infect different kinds of white blood cells. In HME (human monocytic ehrlichiosis), they infect monocytes. In HGE (human granulocytic ehrlichiosis), they infect granulocytes. HGE was renamed anaplasmosis in 2003. Ticks carry many Ehrlichia-like parasites that have not been identified yet. It is likely that the lone star tick transmits HME and that the deer tick transmits HGE.
Ehrlichiosis (HME) was originally thought to be only an animal disease. It was described in humans in 1987 and is now found in 30 states, predominately in the southeast, south-central, and mid-Atlantic states, Europe and Africa. Anaplasmosis (HGE)in humans was first identified in 1990 in a Wisconsin man. Before that it was known to infect horses, sheep, cattle, dogs and cats. It occurs in the upper midwest, northeast, the mid-Atlantic states, northern California, and many parts of Europe. Studies suggest that in endemic areas as much as 15% to 36% of the population has been infected, though often it is not recognized.
The clinical manifestations of ehrlichiosis and anaplasmosis are the same. Each is often characterized by sudden high fever, fatigue, muscle aches, headache. The disease can be mild or life-threatening. Severely ill patients can have low white blood cell count, low platelet count, anemia, elevated liver enzymes, kidney failure and respiratory insufficiency. Older people or people with immune suppression are more likely to require hospitalization. Deaths have occurred.
Diagnosis is limited by our current ability to test for only two species. Ehrlichia parasites multiply inside host cells, forming large mulberry-shaped clusters called morulae which doctors can sometimes see on blood smears. The infection still can easily be missed. The doctor may suspect ehrlichiosis/anaplasmosis in a patient who does not respond well to treatment for Lyme disease.
The treatment of choice for ehrlichiosis/anaplasmosis is doxycycline, with rifampin recommended in case of treatment failure.
Besides the diseases described above, ticks in different geographic areas may be infected with one or more of the following: Colorado tick fever virus; Mycoplasmas; Powassan encephalitis virus; Q Fever; Rocky Mountain spotted fever (Rickettsia); tickborne relapsing fever Borrelia; Tularemia (bacteria). The Tick Chart tells where these diseases are found.
It is certain that we have not yet identified all the diseases that ticks carry and transmit. Coinfections complicate diagnosis and treatment and make recovery even more difficult. Doctors may suspect coinfections in patients who do not respond satisfactorily to antibiotics prescribed for Lyme disease.
There are other possible explanations for treatment failures. People with chronic tickborne infections often have a weakened immune response. This allows other opportunistic infections to flourish, such as HHV-6, CMV, and EBV. These diseases are not necessarily carried by ticks but are widespread in the environment. PCR rather than antibody tests should be used to diagnose these infections. Some people may also have exposure to toxic metals. Specialists should evaluate these cases.
Colorado Tick Fever
Colorado tick fever is caused by a virus carried by Rocky Mountain wood ticks. Symptoms are acute high fever, severe headache, chills, fatigue, and muscle pain.
Mycoplasma species have been identified in ticks. Smaller than bacteria, they invade human cells and disrupt the immune system, causing fatigue, musculoskeletal symptoms, and cognitive problems. Mycoplasmas can be treated with antibiotics.
Powassan virus causes tick-borne encephalitis (TBE). Symptoms may include fever, convulsions, headache, disorientation, lethargy, partial coma and paralysis. Ten percent of patients die and survivors may have permanent damage.
Q fever is caused by Coxiella burnetii, a kind of bacteria carried by cattle, sheep, and goats. Symptoms are similar to those of Lyme disease. Q fever is likely to start with a high fever. Pneumonia and abnormal liver function also suggest Q fever. Doxycycline is the treatment of choice.
Rocky Mountain Spotted Fever
Rocky Mountain spotted fever is caused by bacteria called Rickettsia rickettsii that are transmitted by the bite of a tick. Patients develop high fever, rash, headache and bleeding problems. Thirty percent of untreated patients die. It is treatable with antibiotics, often doxycycline.
Certain ticks secrete a toxin that causes a progressive paralysis, which is reversed when the tick is removed.
Tickborne Relapsing Fever
The agent of tickborne relapsing fever, Borrelia hermsi, is carried by soft ticks of the western United States. It is characterized by cycles of high fever and is treated with antibiotics.
Tularemia, or rabbit fever, occurs throughout the United States. It is caused by the bacterium Francisella tularensis. Symptoms may include skin ulcers, swollen and painful lymph glands, inflamed eyes, sore throat, mouth sores, pneumonia, diarrhea and vomiting. The most effective treatment is with fluorinated quinolones