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Wednesday, July 3, 2013

Another marker or co-infection

Lots of patients are testing positive for Rocky Mountain Spotted Fever. Patients universally have low positive titers.  I do not think most have ever had the disease.  There are many tick borne diseases yet unknown or undiscovered. A Rickettsia bacteria, unclassified, has been reported in a European species of Ixodes ricinus.  This is a novel find.

Rocky Mountain Spotted Fever (RMSF) is caused R. rickettsia.  Patients have spots on their hands which spread to their trunk and these patients are frequently critically ill.  Rickettsia species cause other diseases including typhus. RMSF is not known to be transmitted by small tick, deer ticks or lone start ticks, but transmitted by larger ticks like wood ticks/dog ticks.

I think these positive results are due to cross-reactivity with some yet unknown form of Rickettsia carried by deer ticks.  Some species of Rickettsia may cause little or no clinical illness.  Low positive serology for RMSF may be another marker for the presence of tick borne illness in general.

Like other tick-borne co-infections ( like Anaplasma) , Rickettsia species are all sensitive to doxycycline. 

For this reason, a course of doxycycline should always be incorporated in an antibiotic program used in the treatment of Lyme disease and tick borne illnesses.

1 comment:

LisaT said...

I have checked your blog for insights to rmsf titers before, since, on the canine tick list, I believe that we sometimes see rmsf titers that are indicative of disease, but the disease doesn't act like rmsf is supposed to. (I am a pet owner and long time list member.)

I have wondered if perhaps we don't understand rmsf and there is a chronic form, or if there is some kind of cross-reactivity with other rickettsial diseases.

Rmsf will cross react with R. parkeri, though I know little about that disease, it is thought not to cause severe disease in dogs. There is also this remark, which is intriguing:

"..there is also some emerging information which suggests there may be cases where presence of other, non-Rickettsial, pathogens (e.g., Bartonella vinsonii subspecies berkhoffii) can cause (for unknown reasons) low positive reactions on the RMSF IFA tests."