Human illness can mimic that in pets, and vice versa

Last week my daughter came home from school with a fever. I wasn’t too concerned, parking her on the couch with a blanket and cup of herb tea. As the day turned to evening, however, her temperature continued to rise. She complained of chills, muscle aches, nausea, and headache. I nursed her through the night with cool compresses and alternating doses of acetaminophen and ibuprofen. In the morning she was still sick as the proverbial dog, her temperature now 103 degrees.

“Let me see your hands and feet,” I said softly, trying not to alarm her. As a child who spends countless hours running through fields with dogs and horses, the poor kid has already had Lyme disease twice, but this time the Jewish mother in me was worried about another possibility.

Rocky Mountain Spotted Fever (RMSF) is caused by infection with the bacterium Rickettsia rickettsii. It is carried by the American dog tick, brown dog tick, and Rocky Mountain wood tick. So named because it was first described in people in Montana and Idaho, most cases in the United States are actually seen in the central and southeastern states…and here on Martha’s Vineyard. In humans, illness may develop within days of a tick bite or may take several weeks to appear. Initial symptoms include fever, chills, headache, muscle aches and nausea. Then a red, non-itchy rash often appears on wrists and ankles, spreading to the hands and feet.

I examined my daughter’s extremities. Nada. I rechecked her temperature — 104.4! Since I often see pet owners overreact or, conversely, not recognize the seriousness of certain conditions, I didn’t want to err in either direction. Should I just keep nursing her at home, waiting to see if the fever broke, or was a visit to the doctor in order?

“Dammit, Jim!” I said to myself. “I’m a veterinarian, not a pediatrician!” (No, I have never attended a Star Trek convention but have to admit to having the entire series videotaped and stashed somewhere in my basement.) I called the doctor.

A few days later, in a parallel-universe kind of event, a pediatrician brought me her four-month-old dog, Rocky, on a Sunday emergency visit. “He just isn’t himself,” she confided. Rocky wasn’t eating well and was reluctant to accompany her on their customary morning walk. On physical exam the pup had a slight fever. Normal body temperature in dogs ranges from 101 to 102.5 or even higher if they are excited, anxious, or have been exercising. Rocky’s temperature was 103.7. Definitely a fever but not much of one for a dog, and he looked pretty spunky.

Despite his reluctance to dine at home, he scarfed down my proffered liver treats eagerly. In dogs RMSF usually presents with a sudden onset of high fever, marked lethargy, anorexia, and generalized stiffness. They may also have discharge from eyes and nose, cough, swollen lymph nodes, lameness, nosebleeds, and petechial hemorrhage. They do not get the spotted rash like people do. Left untreated, there can be progressive weakness, loss of balance, staggering, seizures, and eventually death. But right now, all I could say was Rocky had a little fever.

The primary test for RMSF diagnosis in dogs is an antibody titer done at an off-Island reference lab. On the Vineyard, we depend on services like FedEx to transport specimens to these laboratories, and there’s no FedEx service on weekends. “Seeing that it’s Sunday, we have somewhat limited diagnostic options,” I sighed.

A quick in-house test ruled out several other tick-borne diseases — Lyme, Ehrlichiosis, and Anaplasmosis. “He doesn’t look that sick,” I mused as Rocky devoured more liver treats, wiggling around the room. Most dogs I see with RMSF have fevers of 105 or more. They are flat out, lying there like bath mats, with no interest in even the most tempting treats.

But his owner was adamant: Rocky wasn’t well. And she knows him best. “We could do a CBC here today,” I offered, referring to a Complete Blood Count, a simple test that determines the number and distribution of red blood cells, white blood cells, and clotting cells called platelets. RMSF dogs frequently have low platelet counts.

“I’ll have this done in an hour or two,” I told his owner, walking them to the door. “Monitor his temperature at home.” If his fever went down spontaneously and the CBC was normal, we could take the diagnosis of RMSF off the table. If his temperature went up, then we’d take appropriate action.

As I ran the CBC, I pondered my occasional discomfiture when a pet owner is also a physician, knowing that veterinary and human medicine are very different disciplines. I’m never quite sure how much what I know and what they know overlap.

“Drat,” I cussed mildly as the machine spit out the results. The platelet count was borderline. Not high enough to call normal. Not low enough to be definitively abnormal. We still didn’t have an answer.

But Rocky soon gave us more information: that evening, his temperature hit 104 at home. By the next morning he was doing the bath matt imitation that I expect with RMSF. It was Monday so we could send out that titer. We also confirmed the low platelet count with our of–Island lab and started antibiotics.

So we had our diagnosis, right? Well, sort of, maybe. The initial titer came back negative, but that’s not uncommon. In early RMSF, a patient’s immune system may not have had time to mount a significant antibody response. I pondered the advantages when a pet owner is also a physician. She understood when I suggested a “convalescent titer,” i.e., repeating the antibody titer in three or four weeks and see if it goes up.

For now, we have a presumptive diagnosis of RMSF and Rocky is responding beautifully to his antibiotics. My daughter? Luckily, no Rocky Mountain Spotted Fever. Her fever broke that next morning, without her ever getting a rash — or a visit to the doctor.