Diagnostic Tests for Rocky Mountain Spotted Fever and Other Rickettsial Diseases

Case Report: Early Doxycycline Therapy for Potential Rickettsiosis in Critically Ill Patients in Flea-Borne Typhus-Endemic Areas

Flea-borne typhus (FBT), although usually perceived as a self-resolving febrile illness, actually encompasses a wide spectrum of disease severity, including fulminant sepsis with multi-organ failure. In endemic Texas and California, the incidence of FBT has more than doubled over the last decade. Clinicians remain unfamiliar with severe septic presentations of FBT when considering the etiologies of acute undifferentiated febrile syndromes. The diagnostic challenges of FBT include the nonspecific and variable nature of both history and physical examination and the lack of diagnostic testing that can provide clinically relevant information early in the course of infection. These barriers perpetuate misdiagnoses in critically ill patients and lead to delay in initiating appropriate antibiotics, which may contribute to preventable morbidity and mortality. This case series describes the clinical and diagnostic trajectories of three patients who developed FBT-associated multi-organ dysfunction. These patients achieved resolution of infection after receiving doxycycline in the context of a high clinical suspicion. Patients residing in FBT-endemic areas presenting with a febrile illness of unknown etiology with a suggestive constellation of hyponatremia, elevated transaminase levels, and thrombocytopenia should be suspected of having FBT. Clinicians should proceed to serologic testing with early doxycycline therapy for potential rickettsiosis. Familiarizing clinicians with the presentation of rickettsiosis-associated septic syndromes and its early and appropriate antibiotic treatment can provide lifesaving care and reduce health-care costs through prevention of the morbidity associated with FBT.

Murine typhus in a pregnant woman

BACKGROUND

Murine typhus is a flea-borne disease caused by Rickettsia typhi. Although uncommon in most of the United States, it is endemic in Southern California. Most cases are unrecognized given its nonspecific viral symptoms and rare complications.

CASE

A pregnant patient presented with complaints of fever and chills. Physical examination was benign. Laboratory abnormalities included elevated transaminases, proteinuria, and thrombocytopenia. The patient gave a history of exposure to cats and opossums in an area endemic for murine typhus. After empiric treatment with azithromycin, her clinical symptoms and laboratory abnormalities promptly improved. Serologies confirmed acute infection with R. typhi.

CONCLUSION

Although the signs and symptoms of murine typhus can mimic other pregnancy-related complications, a high index of suspicion in endemic areas can lead to the correct diagnosis and prompt treatment.

Application of immunohistochemistry to infections

CONTEXT

Pathologists play an important role in the diagnosis or exclusion of infectious diseases. Traditionally, the diagnosis of infectious diseases rely on serologic assays and cultures. Serologic results may be difficult to interpret in the setting of immunosuppression, fresh tissue is not always available for culture, and culture of fastidious pathogens can be difficult and may take weeks or months to yield a result. Although some microorganisms or their cytopathic effects may be readily identifiable on routine and/or histochemical stains, often these changes are not specific or are sparse in the sample evaluated. In these cases, additional immunohistochemical stains are often needed to establish the diagnosis of infection.

OBJECTIVE

To review the current value and limitations of the use of immunohistochemistry in the diagnosis of infectious diseases in formalin-fixed tissue samples.

DATA SOURCES

Literature in Medline and the authors' own experience.

CONCLUSIONS

Immunohistochemistry has proven to be a useful tool in the diagnosis of infectious diseases in tissue samples. Immunohistochemistry is especially useful in the identification of microorganisms that are present in low numbers, stain poorly, are fastidious to grow, are noncultivable, or exhibit an atypical morphology. Finally, it is important to remember that there may be widespread occurrence of common antigens among bacteria and pathogenic fungi and both monoclonal and polyclonal antibodies must be tested for possible cross-reactivity with other organisms.

Rocky Mountain spotted fever

Rocky Mountain spotted fever (RMSF) is a life-threatening disease caused by Rickettsia rickettsii, an obligately intracellular bacterium that is spread to human beings by ticks. More than a century after its first clinical description, this disease is still among the most virulent human infections identified, being potentially fatal even in previously healthy young people. The diagnosis of RMSF is based on the patient's history and a physical examination, and often presents a dilemma for clinicians because of the non-specific presentation of the disease in its early course. Early empirical treatment is essential to prevent severe complications or a fatal outcome, and treatment should be initiated even in unconfirmed cases. Because there is no vaccine available against RMSF, avoidance of tick-infested areas is still the best way to prevent the infection.

Rocky Mountain spotted fever

Rocky Mountain spotted fever (RMSF) is an unusual but important dermatological condition to identify without hesitation. The classic triad of headache, fever, and a rash that begins on the extremities and travels proximally to involve the trunk is found in a majority of patients. The cutaneous centripetal pattern is a result of cell to cell migration by the causative organism Rickettsia rickettsii. Such individuals should receive prompt antimicrobial therapy and supportive care to avoid serious and potentially fatal complications.

Caracterização de Rickettsia spp. circulante em foco silencioso de febre maculosa brasileira no Município de Caratinga, Minas Gerais, Brasil

O objetivo deste trabalho foi caracterizar Rickettsia spp. circulante em artrópodes vetores no Município de Caratinga, Minas Gerais, Brasil, por meio da PCR, e investigar a presença de anticorpos para riquétsias do grupo da febre maculosa em cães e eqüinos. 2.610 ectoparasitos foram coletados e identificados taxonomicamente. Amostras de DNA obtidas desses vetores foram submetidas à PCR e seqüenciamento. Em pulgas do gênero Ctenocephalides e em carrapatos Amblyomma cajennense foram identificadas seqüências com 100% de homologia com R. felis. Em carrapatos Rhipicephalus sanguineus uma seqüência apresentou 99% de homologia com R. felis e uma seqüência obtida de A. cajennense apresentou 97% de homologia com R. honei e R. rickettsii. Soros de cães (73) e de eqüinos (18) foram submetidos à imunofluorescência indireta (RIFI) usando-se antígeno de R. rickettsii. Apenas três dos soros de eqüinos (17%) mostraram-se positivos. A detecção molecular de riquetsias potencialmente patogênicas ao homem em vetores e a presença de sororeatividade para riquetsias do grupo da febre maculosa em eqüinos, demonstram o risco de transmissão de riquetsioses nessa área e a necessidade de se manter um sistema contínuo de vigilância epidemiológica.

Tick-borne encephalopathies : epidemiology, diagnosis, treatment and prevention

Tick-borne encephalopathies constitute a broad range of infectious diseases affecting the brain and other parts of the CNS. The causative agents are both viral and bacterial. This review focuses on the current most important tick-borne human diseases: tick-borne encephalitis (TBE; including Powassan encephalitis) and Lyme borreliosis. Rocky Mountain spotted fever (RMSF) and Colorado tick fever (CTF), less common tick-borne diseases associated with encephalopathy, are also discussed. TBE is the most important flaviviral infection of the CNS in Europe and Russia, with 10 000-12 000 people diagnosed annually. The lethality of TBE in Europe is 0.5% and a post-encephalitic syndrome is seen in over 40% of affected patients, often producing a pronounced impairment in quality of life. There is no specific treatment for TBE. Two vaccines are available to prevent infection. Although these have a good protection rate and good efficacy, there are few data on long-term immunity. Lyme borreliosis is the most prevalent tick-borne disease in Europe and North America, with >50 000 cases annually. Localised early disease can be treated with oral phenoxymethylpenicillin (penicillin V), doxycycline or amoxicillin. The later manifestations of meningitis, arthritis or acrodermatitis can be treated with oral doxycycline, oral amoxicillin or intravenous ceftriaxone; intravenous benzylpenicillin (penicillin G) or cefotaxime can be used as alternatives. The current use of vaccines against Lyme borreliosis in North America is under discussion, as the LYMErix vaccine has been withdrawn from the market because of possible adverse effects, for example, arthritis. RMSF and CTF appear only in North America. RMSF is an important rickettsial disease and is effectively treated with doxycycline. There is no treatment or preventative measure available for CTF.

Tularemia and Q fever

The zoonotic infections caused by Francisella tularensis and Coxiella burnetii, tularemia and Q fever, respectively, are two less commonly encountered clinical illnesses that are becoming increasingly recognized as epidemiologically important human diseases. The prevalence of tularemia and Q fever can be positively impacted by increased awareness of the clinical entities that arise from infection by these arthropod-borne organisms. Improved recognition of these clinical syndromes will lead to greater diagnostic accuracy in recognizing these diseases in patients. Ultimately, more stringent measures to prevent infection may be required, through raising public awareness, since current therapeutic regimens for these two diseases are limited, and knowledge of the pathogenesis of these two organisms are still in developing stages.

Rocky mountain spotted fever

Rocky mountain spotted fever (RMSF) is a fulminant tick-borne infection by Rickettsia rickettsii. The classical diagnostic triad is fever, headache and rash in a patient with a recent tick bite. With prompt, appropriate antimicrobial therapy, patient outcomes are excellent. However, RMSF is often misdiagnosed, particularly during the initial stages of illness, and as a result, patient outcomes are sometimes suboptimal.

Serious waterborne and wilderness infections

Serious waterborne and wilderness infections are common and usually treatable if diagnosed early. The differential diagnosis for these infections requires a careful and thorough history and physical examination. Common clinical presentations include acute febrile illnesses, altered mental status, diarrhea, or pneumonia. Pathogens causing serious infections include bacteria, fungi, viruses, and protozoa. Epidemiologic help can be obtained from local or state health departments as well as the Centers for Disease Control.

High incidence of Coxiella burnetii markers in a rural population in France

Since Coxiella burnetii, the causative agent of Q fever, is often transmitted from goats and sheep to humans through aerosols, we examined the sera from 168 persons involved in goat breeding in the Centre region of France and 40 members of veterinary and medical staff from the same region for the presence of antibodies against C. burnetii. An immunofluorescence assay was used to detect the presence of antibodies of the IgG isotope against epitopes from phase II of C. burnetii, which are the first antibodies to appear in infected people, and from phase I, which reflect more chronic stages of the infection. Our serological survey showed that most of the tested sera were positive for C. burnetii markers, indicating at least an encounter with the bacterium. In the overall population of 208 subjects, 71% of the sera had antibodies against phase II epitopes (titres > or = 1:40). Among the goat farmers and their immediate families, 78% had antibodies against phase II and 33% against phase I (titres > or = 1:40). Considering only high titres (> or = 1:320), though, only 37% of the farmers had antibodies against phase II and 15% against phase I. Only 3 out of 12 veterinarians working in the field had high titres of antibodies against phase II and phase I, while none of 28 members of veterinary and medical laboratories had significant levels of antibodies. These results emphasize the need for closer surveillance of populations at risk for Q fever, to prevent the infection by C. burnetii from reaching chronic stages of the disease.