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Ehrlichia were first recognized as causes of human infection about twenty years ago ehrlichiosis, erlichiosis. They are very small gram-negative pleomorphic organisms that infect circulating white cells and there are two flavors of ehrlichia - one infects monocytes and the other infects granulocytes. The clinical disease is very similar in both. You will see reports on monocytic ehrlichiosis and granulocytic ehrlichiosis and the clinical presentation is very similar. The monocytic one now has an organism attached to it, called Ehrlichia chafiensus.

This disease is also transmitted by Ixodes ticks, so it can be transmitted with Borrelia burgdorferi, so people can have Lyme disease and ehrlichia at the same time, particularly the granulocytic ehrlichiosis. Most cases in the United States have occurred in the South Central and South Atlantic states, usually in spring and early summer, but this can clearly spread out into late summer and as the weather patterns change around the country, you can see it earlier in the year as well. In this setting, ninety percent have a history of tick exposure in the three weeks prior to illness.

The clinical presentation is a nonspecific flu-like illness. So where this presentation comes in is flu in the summertime. So when you see someone in the office who comes in with a flu-like illness in July, ehrlichia is one of the things that you should think about. GI symptoms can occur in the form of nausea and vomiting in addition to the fever and headache, but they are not universal. They are more common than, for instance, the constitutional symptoms that occur with Lyme disease. So again, in someone with a tick bite who has erythema migrans but who has a lot of nausea and vomiting, one of the things you should think of is ehrlichiosis. The rash occurs but only in twenty percent and when Ehrlichia was first described, it was described as spotless Rocky Mountain spotted fever. It occurs in the same parts of the country, so people were seeing this illness that they thought was Rocky Mountain spotted fever but they didn't see a rash. Now that we know about ehrlichia, it is clear that a lot of those cases were due to ehrlichia.

One of the other differences between Ehrlichia and Lyme disease in the acute setting is that severe disease may occur. By severe we mean multisystemic organ failure. People have presented with acute renal failure, encephalopathy, respiratory failure.

In many places now, you can order an Ehrlichia panel and they will also do other species. It turns out that the granulocytic one cross reacts with some other ehrlichia species that cause diseases in animals - in particular in horses. If you get one back and it says Ehrlichia equii, which is the one in horses, that suggests that it is granulocytic ehrlichiosis. But again, if you just get this one, you may not get that one. We generally look for a minimal titer of 1:64.

The treatment is tetracycline or doxycycline. The dose of doxycycline is the standard dose, which is 100 mg twice daily; tetracycline would be 500 mg four times daily. Most people use doxycycline.

The duration is unknown. There is no data on duration. It is usually given for 7 to 10 days but this is completely empiric. Some people get better without therapy. A question that gets asked is, "I saw somebody who told me they had this illness; they told me they took a tick off of them; I was concerned about this, did a serology and it was positive. They are now all better.

There is no data to answer that question, but you probably do not need to treat them; if they have recovered from their illness, there are no long-term sequelae that can come up later. This is different than Lyme disease in that perspective; they won't pop up with an arthritis.