Incidence of Rocky Mountain spotted fever among American Indians in Oklahoma

OBJECTIVE: Although the state of Oklahoma has traditionally reported very high incidence rates of Rocky Mountain spotted fever (RMSF) cases, the incidence of RMSF among the American Indian population of the state has not been studied. The authors used data from several sources to estimate the incidence of RMSF among American Indians in Oklahoma. METHODS: The authors retrospectively reviewed an Indian Health Service (IHS) hospital discharge database for 1980-1996 and available medical charts from four IHS hospitals. The authors also reviewed RMSF case report forms submitted to the Centers for Disease Control and Prevention (CDC) for 1981-1996. RESULTS: The study data show that American Indians in the IHS Oklahoma City Area were hospitalized with RMSF at an annual rate of 48.2 per million population, compared with an estimated hospitalization rate of 16.9 per million Oklahoma residents. The majority of cases in the IHS database (69%) were diagnosed based on clinical suspicion rather than laboratory confirmation. The incidence of RMSF for Oklahoma American Indians as reported to the CDC was 37.4 cases per million, compared with 21.6 per million for all Oklahoma residents (RR 1.7, 95% confidence interval [CI] 1.5, 2.1). CONCLUSIONS: Rates derived from the IHS database may not be comparable to state and national rates because of differences in case inclusion criteria. However, an analysis of case report forms indicates that American Indians n Oklahoma have a significantly higher incidence of RMSF than that of the overall Oklahoma population. Oklahoma American Indians may benefit from educationa campaigns emphasizing prevention of tick bites and exposure to tick habitats.     

Tick testing as a method of controlling Rocky Mountain spotted fever.

In South Carolina, 1974-1980, only two matches were found between 536 Rocky Mountain spotted fever (RMSF) cases and 965 individuals who submitted ticks that tested rickettsial antigen positive. In neither case did the positive test prevent RMSF. Tick rickettsial positivity rates varied inversely with human RMSF attack rates in different geographic areas. A physician survey established it as unlikely that RMSF occurred in positive tick submitters (PTS), and that although not recommended, 34 per cent of asymptomatic PTS received prophylactic treatment. Only 18 per cent of positive ticks were engorged. Tick testing appears ineffective in preventing RMSF.     

A comparison of serologic methods for diagnosis of Rocky Mountain spotted fever.

Sera referred to the North Carolina Division of Health Services for rickettsial serology in 1974 were tested by complement fixation (CF), microimmunofluorescence (micro-IF), microagglutination (MA) and hemagglutination (HA) for antibodies against Rickettsia rickettsii. There was good agreement among micro-IF,MA and HA tests in detecting antibody responses to this agent, but the CF test was definitely less sensitive than the others, even in illnesses with classical clinical manifestations of Rocky Mountain spotted fever (RMSF). Some variables that seemed to influence the CF result were the slow rate of increase in antibody titers, timing of serum collection, early antibiotic treatment and possibly, the particular association of CF antibody response with the IgG immunoliobulin class. Greater use of these newer, but relatively untried, serodiagnostic procedures is recommended infuture studies of RMSF.     

Fatal cases of Rocky Mountain spotted fever in family clusters--three states, 2003

Rocky Mountain spotted fever (RMSF), a tickborne infection caused by Rickettsia rickettsii and characterized by a rash, has a case-fatality rate as high as 30% in certain untreated patients. Even with treatment, hospitalization rates of 72% and case-fatality rates of 4% have been reported. This report summarizes the clinical course of three fatal cases of RMSF in children and related illness in family members during the summer of 2003. These cases underscore the importance of 1) prompt diagnosis and appropriate antimicrobial therapy in patients with RMSF to prevent deaths and 2) consideration of RMSF as a diagnosis in family members and contacts who have febrile illness and share environmental exposures with the patient.     

Surveillance of Rocky Mountain spotted fever, United States, 1981-1983

The increase in the incidence of RMSF observed in the 1970s appears to have plateaued at a median of 0.49 cases/100,000 for the 6-year period 1978-1983. In 1981-1983, for the first time, Oklahoma had the highest incidence of RMSF in the United States (4.10 cases/100,000/year); increased numbers of cases were also reported from two of the other three West South Central states-Texas and Arkansas. Texas, which reported 217 cases in the 3-year period, had an average incidence of 0.47 cases/100,000/year. This apparent regional increase in RMSF activity may reflect multiple factors, including increased recognition and reporting of cases and environmental factors that may be associated with a true increase in RMSF. Simultaneously, a decrease in the number of cases reported and in the incidence of RMSF have been observed in the South Atlantic states, although these states still account for most (51%) of the cases in the United States. The slight decrease in the case-fatality ratio observed over the last 9 years is unexplained. It may reflect increased awareness of RMSF and result in appropriate and timely treatment. The increasing number and percentage of cases that are laboratory confirmed suggest that the more sensitive and specific laboratory tests now required for serologic confirmation are being more widely used and are contributing to an increased accuracy of reporting of RMSF in this country.(ABSTRACT TRUNCATED AT 250 WORDS)     

The epidemiology of Rocky Mountain spotted fever in Arkansas, Oklahoma, and Texas, 1981 through 1985

From 1981 through 1985, a total of 851 laboratory-confirmed cases of Rocky Mountain spotted fever were reported in Arkansas, Oklahoma, and Texas. Annual incidence rates in each state increased from 1981 through 1983, ranging from a 17% increase in Arkansas to a 137% increase in Texas. In the period 1984 through 1985, the annual incidence rates in each state decreased over 50%. A total of 519 cases were males. A majority of cases (51%) were 19 years of age or younger. April through August were the months of onset of symptoms for 83% of the cases. Differences in distribution of month of onset of symptoms were noted when comparing age groups and state of residence of the cases. The case-fatality ratio was 4.7%. Case-fatality ratios were higher in blacks and in older age groups. An endemic focus of Rocky Mountain spotted fever exists in Arkansas, Oklahoma, and Texas. The annual incidence trend for spotted fever in these three states is dissimilar to the trends in other states.     

Rocky Mountain spotted fever in Georgia, 1961-75: analysis of social and environmental factors affecting occurrence

For the period of 1961 through 1975, 10 geographic and sociologic variables in each of the 159 counties of Georgia were analyzed to determine how they were correlated with the occurrence of Rocky Mountain spotted fever (RMSF). Combinations of variables were transformed into a smaller number of factors using principal-component analysis. Based upon the relative values of these factors, geographic areas of similarity were delineated by cluster analysis. It was found by use of these analyses that the counties of the State formed four similarity clusters, which we called south, central, lower north and upper north. When the incidence of RMSF was subsequently calculated for each of these regions of similarity, the regions had differing RMSF incidence; low in the south and upper north, moderate in the central, and high in the lower north. The four similarity clusters agreed closely with the incidence of RMSF when both were plotted on a map. Thus, when analyzed simultaneously, the 10 variables selected could be used to predict the occurrence of RMSF. The most important variables were those of climate and geography. Of secondary, but still major importance, were the changes over the 15-year period in variables associated with humans and their environmental alterations. Detailed examination of these factors has permitted quantitative evaluation of the simultaneous impacts of the geographic and sociologic variables on the occurrence of RMSF in Georgia. These analyses could be updated to reflect changes in the relevant variables and tested as a means of identifying new high risk areas for RMSF in the State. More generally, this method might be adapted to clarify our understanding of the relative importance of individual variables in the ecology of other diseases or environmental health problems.     

浙江省蜱标本中斑点热群立克次体rOmpA和gltA基因检测

目的了解浙江省部分山区蜱中感染斑点热群立克次体的状况,探讨以外膜蛋白A（rOmpA）和柠檬酸合成酶基因（gltA）为靶基因的PCR方法可行性。方法利用PCR方法,检测天台县左溪镇和临安县西天目地区共46组蜱类标本中rOmpA和gltA基因特异片段。对所检测到的阳性结果进行克隆与序列测定,并进行聚类分析。结果从46组蜱标本中检测发现2组长角血蜱中斑点热群立克次体的rOmpA和gltA基因片段均为阳性,核酸序列基本一致,但推测斑点热群立克次体种的进化位置存在差异。结论浙江省部分山区存在蜱中感染斑点热群立克次体的状况。利用rOmpA和gltA基因能从标本中检测到斑点热群立克次体,但从2个结果推测立克次体的分类位置存在差异。     

Consequences of delayed diagnosis of Rocky Mountain spotted fever in children--West Virginia, Michigan, Tennessee, and Oklahoma, May-July 2000

Patients with Rocky Mountain spotted fever (RMSF), a tickborne infection caused by Rickettsia rickettsii, respond quickly to tetracycline-class antibiotics (e.g., doxycycline) when therapy is started within the first few days of illness; however, untreated RMSF may result in severe illness and death. Persons aged <10 years have the highest age-specific incidence of RMSF. This report summarizes the clinical course and outcome of RMSF in four children from four regions of the United States and underscores the need for clinicians throughout the United States to consider RMSF in children with rash and fever, particularly those with a history of tick bite or who present during April-September when approximately 90% of RMSF cases occur.     

Isolation of an agent of the spotted fever group rickettsia from tick eggs in Madrid, Spain.

Ticks recovered from dogs in rural villages around Madrid (Spain) were processed to isolate rickettsiae. One sample containing mixtures of ticks and four containing eggs, in which rickettsiae had been detected by indirect immunofluorescence with a human serum highly reactive to Rickettsia conorii, were decontaminated, homogenized and inoculated onto Vero cells. Two egg samples yielded a cytopathic agent that reacted positively by immunofluorescence. One sample (14H) was successfully subcultured and identified as a member of the spotted fever group rickettsia. Tick eggs provide suitable material for isolation of rickettsia.     

Surface protein Adr2 of Rickettsia rickettsii induced protective immunity against Rocky Mountain spotted fever in C3H/HeN mice

Background

Rickettsia rickettsii is the pathogen of Rocky Mountain spotted fever (RMSF), a life-threatening tick-transmitted infection. Adr2 was a surface-exposed adhesion protein of R. rickettsii and its immunoprotection against RMSF was investigated in mice.

Methods

Recombinant Adr2 (rAdr2) was used to immunize C3H/HeN mice, and the rickettsial loads in organs of the mice were detected after challenge with R. rickettsii. The levels of specific antibodies of sera from the immunized mice were determined and the sera from immunized mice were applied to neutralize R. rickettsii. Proliferation and cytokine secretion of CD4⁺ and CD8⁺ T cells isolated from R. rickettsii-infected mice were also assayed after rAdr2 stimulation.

Results

After R. rickettsii challenge, the rickettsial loads in spleens, livers, and lungs were significantly lower and the impairment degrees of these organs in rAdr2-immunized mice were markedly slighter, compared with those in negative control mice. The ratio of specific IgG2a/IgG1 of rAdr2-immunized mice kept increasing during the immunization. After treatment with rAdr2-immunized sera, the total number of R. rickettsii organisms adhering and invading host cells was significantly lower than that treated with PBS-immunized sera. Interferon-γ secretion by CD4⁺ or CD8⁺ T cells and tumor necrosis factor-α secretion by CD4⁺ T cells from R. rickettsii-infected mice were respectively significantly greater than those from uninfected mice after rAdr2 stimulation.

Conclusion

Adr2 is a protective antigen of R. rickettsii. Protection offered by Adr2 is mainly dependent on antigen-specific cell-mediated immune responses, including efficient activity of CD4⁺ and CD8⁺ T cells to produce great amount of TNF-α and/or IFN-γ as well as rapid increase of specific IgG2a, which synergistically activate and opsonize host cells to killing intracellular rickettsiae.