Rocky Mountain spotted fever in Native Americans

Abstract

As far as human infections go, Rocky Mountain spotted fever (RMSF) has not posed a global risk or even a large regional epidemic. However, it has become an emerging public health issue in several Native American reservations in the US state of Arizona. But what is unique about the outbreak in Arizona is that transmission has been linked to a new vector, the brown dog tick (Rhipicephalus sanguineus sensu lato), which has not been previously shown to transmit RMSF infection in the USA. From 2002 to 2014, there have been more than 300 cases of RMSF and 20 related deaths in Native Americans. The average annual incidence for 2009–12 was roughly 136 cases per 100 000 people on the three reservations that were the most heavily aff ected, which was more than 150 times the national average. The case-fatality rate in Arizona is also markedly higher than currently observed elsewhere in the USA, averaging 7% of reported cases compared with less than 1% nationally. Among young Native American children aged between 5 and 9 years, the case-fatality rate was signifi cantly higher (11·5% vs 1·7%) compared with white children. In addition to the human toll, the total cost of medical care, loss of productivity, and death in people infected with RMSF on two Native American reservations in Arizona amounts to about US$13·2 million, according to a study from the Center for Disease Control and Prevention (CDC). CDC also believe their data to be substantially underestimating of the cost of the epidemic. As of 2014, there are now six Native American reservations in Arizona with documented cases in human beings, which puts more than 350 000 individuals at risk of infection. “There is no biological factor that predisposes American Indians to RMSF” said Naomi Drexler, an epidemiologist from the Rickettsial Zoonoses Branch, CDC. “If they are exposed to the ticks they can become infected, and one reason for the high exposure are the large populations of dogs in these communities.”