James Occi, PhD, May Awareness Guest Blog – Rickettsiosis: “New” RMSF

by James Occi*

Early History of RMSF – Rocky Mountain spotted fever (RMSF) was discovered by Howard Taylor  Ricketts in the early 1900s in the Bitterroot Mountains of Montana and Idaho.  RMSF is a bacterial infection (caused by Rickettsia rickettsii) that is transmitted by the Rocky Mountain wood tick, Dermacentor andersoni. RMSF is quite fatal if not treated or if there is a delay in diagnosis.

In the 1940s, RMSF was identified east of the Mississippi and was transmitted by the American dog tick (ADT), Dermacentor variabilis. The cases occurring in this newly identified region were not as severe – thought to be the results of strain differences in the pathogen. Currently most cases of RMSF are found in the mid-Atlantic and southeastern states and not the Rocky Mountains.

However, there are some inconsistencies in the claim that the ADT transmits R. rickettsii on the eastern seaboard. And when I give a seminar and show a slide of the ADT and the agent(s) it may transmit, I put a question mark by RMSF.

Is American Dog Tick Transmitting RMSF in East? – So, let’s look at the evidence (or the lack thereof) that we have. First, there are >20 species of Rickettsia that are pathogenic to humans in some way shape or form. These are called collectively, the “spotted fever group rickettsia” or SFGR.

Second, most cases of Spotted fever rickettsia (SFR) are diagnosed clinically.  “You were in the woods, had a tick bite and now you have a fever and rash?”  Here is some doxycycline, end of story (hopefully).  If the physician does send out blood for serology, the clinical assay cross reacts with any spotted fever rickettsia – even “non-pathogenic” species like R. amblyommatis (present in 20-30% of lone star ticks, Amblyomma americanum). The current test cannot identify the infecting species of Rickettsia.  The good news is from a clinician’s standpoint, it doesn’t matter which Rickettsia it is (nor do they usually care) because the treatment is the same!  So, to the public and medical community, it doesn’t matter which species it is.  But we are scientists and curious, and we want a clearer understanding as to what “spotted fever group rickettsiosis” is.

Third, entomologist and public health scientists in the southeast and mid-Atlantic region in the early 2000s noticed that there was an increase in SFR, with a decline in mortality.  They also did surveys throughout these states and noticed that in some states >90% of tick submissions were lone star ticks with SFR and few ADTs.

American Dog Tick Studies – Then the entomologists started collecting ADTs to look for R. rickettsii. Let me
summarize just a few studies which are reviewed in Occi et al 2020, Table 1.¹ (Most of these studies did find other SFGR at very low prevalences, but they were not pathogenic species.)

1. In Tennessee, 548 ADTs were tested and no R. rickettsii was found.
2. In Virginia 2,276 ADTs were tested and no R. rickettsii was found.
3. In another study in TN, 2,515 ADTs were tested and no R. rickettsii was found.
4. A multi-state study tested 1,400 ADTs from in the mid-Atlantic region, and only 1 was infected with R. rickettsii.
5. I tested over 800 ADTs in NJ for SFR and no R. rickettsii (Occi et al. 2020)

Confusion Between What Ticks Transmit What Rickettsia – Many scientists in the field have surmised that “we don’t know what ADTs are transmitting nor which Rickettsia is infecting people.”  In fact, most health departments now call it “spotted fever group rickettsiosis” instead of RMSF. Moreover, we don’t even know which species of tick is transmitting this enigmatic bacterium or bacteria. One cannot even entertain the idea of a control program if one does not know which tick is involved (keep in mind, there are very few tick control programs in existence).

Bottom Line – So, what do we do from patient advocacy/public health standpoints? I think the only thing we can do for now is maintain the same messaging:  protective clothing, tick checks, repellants and keep vigilant and continue to study the vectors and strains they transmit. 

1 Occi, J., A. M. Egizi, A. Goncalves, and D. M. Fonseca. 2020. New Jersey-Wide Survey of Spotted Fever Group Rickettsia (Proteobacteria: Rickettsiaceae) in Dermacentor variabilis and Amblyomma americanum (Acari: Ixodida: Ixodidae). The American journal of tropical medicine and hygiene 103: 1009-1016.

*Author Note: The opinions expressed in this Blog are personal opinions of author James Occi MA, MS, PhD, only and do not necessarily reflect those of any other entity.