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Rocky Mountain Spotted Fever

Rocky Mountain spotted fever, the spotted form of ehrlichiosis, is the most frequently reported rickettsial disease in the United States. There are two tick species responsible for transmission - different ones in the east and in the west. Rickettsial organisms are released from the salivary glands of ticks during a six-hour attachment. These ticks are bigger - these are dog ticks - these ticks are as big as your fingernail. When they are engorged, they can be even bigger than that. The rickettsial organisms that are released only require a six-hour attachment. So this is a disease that can be transmitted after a shorter period of attachment.

The name of Rocky Mountain spotted fever is a misnomer. It is widely distributed across the United States and now, most infections are acquired in the South Atlantic or coastal states. You do see it in the western United States, but it is actually more commonly reported from the South Central Atlantic states. Ninety-five percent of infections occur between April and September. You do occasionally see urban foci of this disease.

The clinical presentation of Rocky Mountain spotted fever is very similar to the presentation of ehrlichiosis, with the exception of the rash. The triad that you look for here is fever, rash, tick exposure. So that person who comes in to see you with the summer flu, if they have the rash that is what should make you think about Rocky Mountain spotted fever. This illness usually occurs five to seven days after the exposure and it is abrupt. They present with the acute onset of high fever, severe headache.

The rash typically begins within a day to two weeks after the illness begins, so people are sick before they get the rash and then the rash starts. It begins on the wrists and ankles and spreads centrally.

The laboratory abnormalities here again are nonspecific, but they are very similar to those we see with ehrlichiosis - leukopenia, thrombocytopenia, elevated liver function tests, hyponatremia. In this disease, the spinal fluid is usually normal, so that is a little bit different from Ehrlichia, where you do see cells in the spinal fluid. Again, in terms of treatment, tetracycline is recommended - you may need to give it parenterally here if someone is sick enough that they can't take it orally. If they can take oral medications, there is no reason not to use tetracycline. Treatment in this disease is important. In contrast with the Ehrlichia patient who may be asymptomatic, treatment here decreases mortality significantly and actually the poor outcomes that are associated with Rocky Mountain spotted fever, one of the major factors of poor outcomes, is a delay in treatment. If you want to treat, those people are going to do worse. If you suspect this disease, you need to begin the person on treatment empirically. The poor outcome is usually due to a disseminated vasculitis. This organism is a vascular tropic organism; it likes blood cells, it likes the endothelium in particular and that is why you get the gangrenous lesions in the skin. That is associated with mortality.

The diagnosis can be made by skin biopsy. This is actually the most rapid way to make diagnosis, is to biopsy a skin lesion and show the organism. Unfortunately, that is not always an available technique, so we rely on serologic tests as well here. Antibodies can generally be detected within 7 to 10 days of illness. Again, this is one of those illness where if you suspect it, you need to treat, do the blood test and then wait for the results to come back. There is cross reaction between Rocky Mountain spotted fever and other rickettsial infections, so you need to do acute and convalescent titers specifically looking for rickettsiae, which is the causative agent here.

I wanted to mention something about tick paralysis. Again, there can be a very dramatic recovery from what appears to catastrophic illness. Tick paralysis is due to a neurotoxin that is produced in the saliva of a tick. Symptoms can occur within two to seven days of exposure. Most cases from the United States have been reported from the Pacific Northwest, but they can occur anywhere in the United States. The typical mimic here is Guillain-Barre. This is someone who presents with a symmetric ascending paralysis, or weakness, with a suggestion of the diagnosis of Guillain-Barre. However, there is either something unusual about the presentation, like you can't find an antecedent illness, or they are just in an area where they could be outdoors and have exposure. You should look for ticks and most commonly they are found in the scalp.