There are a number of infectious diseases transmitted through tick bites, including Lyme disease and Rickettsia, Babesiosis, and Ehrlichiosis. Unfortunately, many of these exist as co-infections which remain unrecognized and untreated, meaning that the infection that is treated may appear to be resistant to therapy when it is in fact another bacterium causing the persistent symptoms. Physicians will increasingly need to be able to distinguish between these types of vector-borne diseases as the tick population becomes more widespread and present in urban areas. The overlap between symptoms of Lyme disease and Rickettsia can present some specific challenges to clinicians during diagnosis and treatment, with antibiotics sometimes working for one but not for another.
Unlike Lyme disease, the causal agent of Rickettsia can be transmitted via tick bite within six to ten hours, meaning that someone can be infected with Rickettsia, but not Lyme disease, from a tick carrying both types or organism. Most infections with Rickettsia rickettsiae occur in the southeast and west south-central regions of the United States, with hundreds of cases reported each year. Also known as Rocky Mountain Spotted Fever, the infection can be fatal in severe cases with the first signs and symptoms of Rickettsia usually seen within five to ten days of the initial tick bite. In most cases, however, Rickettsia is a singular infection as it is carried and transmitted by a specific type of tick that does not normally carry Lyme disease or common co-infectious organisms. The American Dog Tick, the lone-star tick, and the wood tick live in wooded areas, and grassy fields and the infection is most common in the spring and summer as ticks are more active and people are more exposed to ticks through outdoor activities.
Treating Rickettsia and Lyme Disease
Waiting for Lyme disease test results or confirmation of Rickettsia before beginning antibiotics may mean that the optimum treatment window is missed. Diagnosis must, therefore, be made before laboratory confirmation, using patients’ symptoms and history instead. Antibodies to Rickettsia rickettsiae form within seven to ten days of the first symptoms but decline within two months, meaning that some persistent infections can be missed during this diagnostic period. Rickettsia used to be fatal in a quarter of all cases but the mortality rate has now been brought down to 5% with prompt treatment with tetracyclines recommended for adults with Rocky Mountain Spotted Fever (RMSF).
Rickettsia in Children and CNS Involvement
Children are not normally given tetracycline antibiotics, even for Rickettsia infection, with chloramphenicol the preferred treatment for those under eight years of age. This is given intravenously in cases of central nervous system infection and is recommended to continue for five days to a week, or for at least two days after the patient’s’ fever is resolved.
One key difference between Rickettsia and Lyme disease is that those who survive infection with Rocky Mountain Spotted Fever develop permanent immunity whereas Lyme disease infection can occur over and over again, with some people believing that this is the real cause of many cases of ‘chronic’ Lyme disease.
Lyme Disease Co-Infections
Where Lyme disease is suspected and a co-infection with ehrlichiosis cannot be ruled out, patients are recommended to be treated with doxycycline as this is effective against both organisms. The symptoms of Rickettsia can be quite distinct, including the rash beginning on the wrists and ankles and working inwards on the body. Where such symptoms are observed the patient will also normally be prescribed doxycycline as the tetracycline group of antibiotics is also effective against this potential Lyme disease co-infection. Rickettsia is one of the least likely co-infections with Lyme disease as it is usually spread by a different type of tick, but physicians will still need to be alert to the signs of both infections, especially in areas where both tick types reside.