What’s Eating You? Rhipicephalus Ticks Revisited
Rhipicephalus ticks are vectors of disease in humans and animals. Rhipicephalus sanguineus sensu lato (the brown dog tick) is one of the most geographically widespread tick species worldwide, likely due to its ability to colonize human and canine dwellings over a range of habitats. They transmit a variety of diseases to dogs and humans, including canine babesiosis, canine monocytic ehrlichiosis, hepatozoonosis, Mediterranean spotted fever, and Rocky Mountain spotted fever. Tick bites manifest as intensely pruritic, erythematous papules at the site of tick attachment; symptomatic relief usually can be achieved with topical antipruritics. Prevention of tick bites is best achieved through a combination of veterinary and environmental control; protective clothing; repellents, such as N,N-diethyl-meta-toluamide (DEET) and permethrin; and prompt identification and removal of ticks.
PRACTICE POINTS
- Rhipicephalus ticks are vectors of a variety of diseases, including the rickettsial diseases Rocky Mountain spotted fever and Mediterranean spotted fever.
- Presenting symptoms of a tick bite include intensely pruritic, erythematous papules and nodules at the site of tick attachment.
- If rickettsial disease is suspected, treatment with doxycycline should be initiated immediately; do not delay treatment to await results of confirmatory tests or because of the absence of a rash.
- Primary methods of prevention of tick-borne disease include repellents, protective clothing, vector control, and prompt removal of the tick.
Patients do not become antibody positive until 7 to 10 days after symptoms begin; therefore, treatment should not be delayed while awaiting serologic test results. The case fatality rate in the United States is estimated to be 5% to 10% overall and as high as 40% to 50% among patients who are not treated until day 8 or 9 of illness.17
Cutaneous complications include skin necrosis and gangrene due to continuous tissue damage in severe cases.16 Severe infection also may manifest with signs of multiorgan system damage, including altered mental status, cerebral edema, meningismus, transient deafness, myocarditis, pulmonary hemorrhage and edema, conjunctivitis, retinal abnormalities, and acute renal failure.14,16 Risk factors for more severe illness include delayed treatment, age 40 years or older or younger than 10 years, and underlying medical conditions such as alcoholic liver disease and glucose-6-phosphate dehydrogenase deficiency. However, even some healthy young patients die of this disease.17
Mediterranean Spotted Fever—Rhipicephalus sanguineus sensu lato is the primary vector of MSF, which is prevalent in areas adjacent to the Mediterranean Sea, including southern Europe, Africa, and Central Asia; Sicily is the most highly affected region.18 Findings with MSF are nearly identical to those of RMSF, except that tache noire is more common, present in as many as 70% of cases at the site of the inoculating tick bite, and MSF typically follows a less severe clinical course.12 Similar to other rickettsial diseases, the pathogenesis of MSF involves direct injury to vascular endothelial cells, causing a vasculitis that is responsible for the clinical abnormalities observed.
Patients with severe MSF experience complications similar to severe RMSF, including neurologic manifestations and multiorgan damage.18 Risk factors include advanced age, immunocompromised state, cardiac disease, chronic alcoholism, diabetes mellitus, glucose-6-phosphate dehydrogenase deficiency, respiratory insufficiency, and delayed treatment.18
Treatment—For all spotted fever group rickettsial infections, doxycycline is the treatment of choice for all patients, including children and pregnant women. Treatment should be started without delay; recommended dosages are 100 mg twice daily for children weighing more than 45 kg and adults, and 2.2 mg/kg twice daily for children weighing 45 kg or less.12
Rhipicephalus tick bites rarely can result in paralysis; however, Dermacentor ticks are responsible for most cases of tick-related paralysis in North America. Other pathogens proven or reputed to be transmitted by Rhipicephalus sanguineus sensu lato with zoonotic potential include but are not limited to Rickettsia massiliae, Coxiella burnetti, Anaplasma platys, Leishmania infantum, and Crimean-Congo hemorrhagic fever virus (Nairovirus).19
Environmental Treatment and Prevention
The most effective way to prevent tick-borne illness is avoidance of tick bites. Primary prevention methods include vector control, use of repellents (eg, N,N-diethyl-meta-toluamide [DEET]), picaridin, permethrin), avoidance of areas with a high tick burden, use of protective clothing, and detection and removal of ticks as soon as possible.
