Jennifer H. McQuiston

Q Fever in Humans and Animals in the United States

Coxiella burnetii, the etiologic agent of Q fever, is a worldwide zoonotic pathogen. Although Q fever is present in the United States, little is known about its current incidence or geographic distribution in either humans or animals. Published reports of national disease surveillance, individual cases, outbreak investigations, and serologic surveys were reviewed to better characterize Q fever epidemiology in the United States. In national disease surveillance reports for 1948-1986, 1,396 human cases were reported from almost every state. Among published individual case reports and outbreak investigations, occupational exposures (research facilities, farm environments, slaughterhouses) were commonly reported, and sheep were most frequently implicated as a possible source of infection. In studies conducted on specific groups, livestock handlers had a significantly higher prevalence of antibodies to C. burnetii than did persons with no known risk. Animal studies showed wide variation in seroprevalence, with goats having a significantly higher average seroprevalence (41.6%) than sheep (16.5%) or cattle (3.4%). Evidence of antibody to C. burnetii was reported among various wild-animal species, including coyotes, foxes, rodents, skunks, raccoons, rabbits, deer, and birds. This literature review suggests that C. burnetii is enzootic among ruminants and wild animals throughout much of the United States and that there is widespread human exposure to this pathogen. Sheep and goats appear to be a more important risk for human infection in the United States than cattle or wild animals, and research studies examining the natural history and transmission risk of Q fever in sheep and goats in this country should be encouraged.

Emergence of a New Pathogenic Ehrlichia Species, Wisconsin and Minnesota, 2009

BACKGROUND Ehrlichiosis is a clinically important, emerging zoonosis. Only Ehrlichia chaffeensis and E. ewingii have been thought to cause ehrlichiosis in humans in the United States. Patients with suspected ehrlichiosis routinely undergo testing to ensure proper diagnosis and to ascertain the cause. METHODS We used molecular methods, culturing, and serologic testing to diagnose and ascertain the cause of cases of ehrlichiosis. RESULTS On testing, four cases of ehrlichiosis in Minnesota or Wisconsin were found not to be from E. chaffeensis or E. ewingii and instead to be caused by a newly discovered ehrlichia species. All patients had fever, malaise, headache, and lymphopenia; three had thrombocytopenia; and two had elevated liver-enzyme levels. All recovered after receiving doxycycline treatment. At least 17 of 697 Ixodes scapularis ticks collected in Minnesota or Wisconsin were positive for the same ehrlichia species on polymerase-chain-reaction testing. Genetic analyses revealed that this new ehrlichia species is closely related to E. muris. CONCLUSIONS We report a new ehrlichia species in Minnesota and Wisconsin and provide supportive clinical, epidemiologic, culture, DNA-sequence, and vector data. Physicians need to be aware of this newly discovered close relative of E. muris to ensure appropriate testing, treatment, and regional surveillance. (Funded by the National Institutes of Health and the Centers for Disease Control and Prevention.).

The increasing recognition of rickettsial pathogens in dogs and people

Dogs and people are exposed to and susceptible to infection by many of the same tick-borne bacterial pathogens in the order Rickettsiales, including Anaplasma phagocytophilum, Ehrlichia canis, E. chaffeensis, E. ewingii, Rickettsia rickettsii, R. conorii, and other spotted fever group rickettsiae. Recent findings include descriptions of novel Ehrlichia and Rickettsia species, recognition of the occurrence and clinical significance of co-infection, and increasing awareness of Rhipicephalus sanguineus-associated diseases. Newer molecular assays are available, although renewed efforts to encourage their use are needed. This review highlights the ecology and epidemiology of these diseases, and proposes avenues for future investigation.

Analysis of Risk Factors for Fatal Rocky Mountain Spotted Fever: Evidence for Superiority of Tetracyclines for Therapy

Epidemiologic and clinical characteristics of fatal and nonfatal cases of Rocky Mountain spotted fever (RMSF) were compared to identify risk factors for death caused by this disease. Confirmed and probable RMSF cases reported through US national surveillance for 1981-1998 were analyzed. Among 6388 RMSF patients, 213 died (annual case-fatality rate, 3.3%; range, 4.9% in 1982 to 1.1% in 1996). Use of tetracycline-class antibiotics for treatment of RMSF increased significantly in the 1990s, compared with use in the 1980s. Older patients, patients treated with chloramphenicol only, patients for whom tetracycline antibiotics were not the primary therapy, and patients for whom treatment was delayed > or =5 days after the onset of symptoms were at higher risk for death. Although the case-fatality rate was lower in the 1990s than in the 1980s, risk factors for fatal RMSF were similar. Despite the availability of effective antibiotics, RMSF-related deaths continue to occur because of delayed diagnosis and failure to use appropriate therapy.

Rocky Mountain Spotted Fever in the United States, 1997–2002

Abstract:  The increased incidence of Rocky Mountain spotted fever (RMSF) in 1997–2002 compared with previous years may be related to enhanced awareness and reporting of RMSF as well as changes in human–vector interaction. However, reports on RMSF mortality underscore the need for physician vigilance in considering a diagnosis of RMSF for febrile individuals potentially exposed to ticks and stress the importance of treating such persons regardless of the presence of a rash.

Transmission of tick-borne agents of disease by blood transfusion: a review of known and potential risks in the United States

Tick-borne infectious diseases, such as babesiosis, the ehrlichioses, Lyme disease, and Rocky Mountain spotted fever (RMSF), are important public health concerns in the United States. With the exception of RMSF, these diseases have been recognized in the United States only in the last 30 years, and characteristics of epidemiology, prevalence, and pathogenesis are still being elucidated. Each of the agents of these zoonotic diseases is transmitted to humans through the bites of infected ticks, which acquire infection from animal reservoirs. The causative agents of these diseases are biologically diverse. Babesiosis is caused by multiple species of intracellular protozoan parasites, whereas Lyme disease is caused by a spirochete. RMSF and the ehrlichioses are caused by obligate intracellular bacterial pathogens. Although the etiologic agents differ, the diseases they cause share many epidemiologic characteristics. Because these pathogens may circulate in the blood, human-to-human transmission via blood transfusions is theoretically possible. However, the risks these agents pose to the nation’s blood supply remain largely undefined. There have been more than 20 documented cases of babesiosis transmitted by blood transfusion1-7 and a single reported case of transfusiontransmitted RMSF.8 To date, there have been no confirmed reports of Lyme disease transmitted by blood transfusions, and only a single possible case of transfusion-transmitted ehrlichiosis.9 Public health concern about the possible risk for transfusion transmission of tick-borne agents increased after a 1997 voluntary recall of potentially infectious blood components that had been donated by National Guard members, several of whom subsequently developed ehrlichiosis or RMSF.10 Although no cases of transfusiontransmitted illness were detected in recipients of these blood components, this event underscored the need to better evaluate the possibility of transmission of tick-borne agents through the blood supply. In January 1999, the CDC, the FDA, the National Institutes of Health, and the Department of Defense convened a workshop in Atlanta, GA, entitled “The potential for transfusion transmission of tick-borne agents.” Participants included representatives from blood collection agencies, professional organizations, state and local health departments, and researchers in the field of tick-borne diseases. The primary objectives of this workshop were 1) to review current information on the epidemiologic and biologic characteristics of tick-borne agents of disease that make the transfusion transmission of such agents possible; 2) to identify risks, if any, that tick-borne agents pose to the United States’ blood supply; 3) to identify research needs related to the development of diagnostic tests for tick-borne diseases; and 4) to assess whether changes in blood-collection policies are needed to reduce the risk of transfusion transmission of tick-borne diseases. This article reviews the major topics that were discussed at this workshop.

Rocky Mountain Spotted Fever in the United States, 2000–2007: Interpreting Contemporary Increases in Incidence

Rocky Mountain spotted fever (RMSF), a potentially fatal tick-borne infection caused by Rickettsia rickettsii, is considered a notifiable condition in the United States. During 2000 to 2007, the annual reported incidence of RMSF increased from 1.7 to 7 cases per million persons from 2000 to 2007, the highest rate ever recorded. American Indians had a significantly higher incidence than other race groups. Children 5-9 years of age appeared at highest risk for fatal outcome. Enzyme-linked immunosorbent assays became more widely available beginning in 2004 and were used to diagnose 38% of cases during 2005-2007. The proportion of cases classified as confirmed RMSF decreased from 15% in 2000 to 4% in 2007. Concomitantly, case fatality decreased from 2.2% to 0.3%. The decreasing proportion of confirmed cases and cases with fatal outcome suggests that changes in diagnostic and surveillance practices may be influencing the observed increase in reported incidence rates.

Increasing Incidence of Ehrlichia chaffeensis and Anaplasma phagocytophilum in the United States, 2000–2007

Ehrlichia chaffeensis causes human monocytic ehrlichiosis, and Anaplasma phagocytophilum causes human granulocytic anaplasmosis. These related tick-borne rickettsial organisms can cause severe and fatal illness. During 2000-2007, the reported incidence rate of E. chaffeensis increased from 0.80 to 3.0 cases/million persons/year. The case-fatality rate was 1.9%, and the hospitalization rate was 49%. During 2000-2007, the reported incidence of A. phagocytophilum increased from 1.4 to 3.0 cases/million persons/year. The case-fatality rate was 0.6%, and the hospitalization rate was 36%. Rates among female patients were lower than among male patients for ehrlichiosis (rate ratio = 0.68) and anaplasmosis (rate ratio = 0.70). Most (80%) ehrlichiosis and anaplasmosis cases met only a probable case definition, although, use of a polymerase chain reaction to confirm infections increased during 2000-2007. Heightened reporting of these diseases will likely continue with improving recognition, changing surveillance practices, and appropriate application of diagnostic assays.

No Visible Dental Staining in Children Treated with Doxycycline for Suspected Rocky Mountain Spotted Fever

OBJECTIVE To evaluate whether cosmetically relevant dental effects occurred among children who had received doxycycline for treatment of suspected Rocky Mountain spotted fever (RMSF). STUDY DESIGN Children who lived on an American Indian reservation with high incidence of RMSF were classified as exposed or unexposed to doxycycline, based on medical and pharmacy record abstraction. Licensed, trained dentists examined each childs teeth and evaluated visible staining patterns and enamel hypoplasia. Objective tooth color was evaluated with a spectrophotometer. RESULTS Fifty-eight children who received an average of 1.8 courses of doxycycline before 8 years of age and who now had exposed permanent teeth erupted were compared with 213 children who had never received doxycycline. No tetracycline-like staining was observed in any of the exposed childrens teeth (0/58, 95% CI 0%-5%), and no significant difference in tooth shade (P=.20) or hypoplasia (P=1.0) was found between the 2 groups. CONCLUSIONS This study failed to demonstrate dental staining, enamel hypoplasia, or tooth color differences among children who received short-term courses of doxycycline at <8 years of age. Healthcare provider confidence in use of doxycycline for suspected RMSF in children may be improved by modifying the drugs label.

Murine Typhus in Austin, Texas, USA, 2008

Physicians should be alert for possible cases in this area.