Rickettsioses are caused by species of Rickettsia, a genus comprising organisms characterized by their strictly intracellular location and their association with arthropods. Rickettsia species are difficult to cultivate in vitro and exhibit strong serological cross-reactions with each other. These technical difficulties long prohibited a detailed study of the rickettsiae, and it is only following the recent introduction of novel laboratory methods that progress in this field has been possible. In this review, we discuss the impact that these practical innovations have had on the study of rickettsiae. Prior to 1986, only eight rickettsioses were clinically recognized; however, in the last 10 years, an additional six have been discovered. We describe the different steps that resulted in the description of each new rickettsiosis and discuss the influence of factors as diverse as physicians' curiosity and the adoption of molecular biology-based identification in helping to recognize these new infections. We also assess the pathogenic potential of rickettsial strains that to date have been associated only with arthropods, and we discuss diseases of unknown etiology that may be rickettsioses.

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Rickettsioses as paradigms of new or emerging infectious diseases.

Rodents are the most abundant and diversified order of living mammals in the world. Already since the Middle Ages we know that they can contribute to human disease, as black rats were associated with distribution of plague. However, also in modern times rodents form a threat for public health. In this review article a large number of pathogens that are directly or indirectly transmitted by rodents are described. Moreover, a simplified rodent disease model is discussed.

Rodent-borne diseases and their risks for public health

Morbidity and mortality caused by rickettsioses have had a major influence on military activities and public health for >2000 years. The threat posed by the rickettsioses is reviewed, focusing on the impact and epidemiology of those that have adversely influenced wartime operations and the current challenges posed by these diseases. With their uneven worldwide distribution, the discovery of drug-refractory strains of Orientia tsutsugamushi, the increased threat of their use in acts of bioterrorism, frequent deployment of troops to regions of endemicity, and exposures due to increased humanitarian missions, these diseases continue to be a threat to military personnel in the field. Effective strategies to reduce the impact of these diseases include development of effective vaccines, enhanced surveillance, and development of new safe, effective, and odorless repellants. The continuation of a proven, highly productive military infectious disease research program is essential for providing solutions to these daunting tasks.

The past and present threat of rickettsial diseases to military medicine and international public health.

A wide variety of stains are useful for detection of different organisms or, for viruses, the cytopathologic changes they induce, in smears prepared directly from clinical specimens and in tissue sections. Other types of stains, such as hematoxylin and eosin, are used routinely to stain tissue sections and are most valuable for assessing the immunologic response of the host to the invading pathogen. In many cases, the pattern of inflammation provides important clues to diagnosis and helps to guide the selection of additional "special" stains used predominantly for diagnosis of infectious diseases. A stain may be nonspecific, allowing detection of a spectrum of organisms, as do the Papanicolaou stain and silver impregnation methods, or detection of only a limited group of organisms, as do the different acid-fast techniques. Some nonspecific stains, such as the Gram stain, are differential and provide valuable preliminary information concerning identification. Immunohistochemical stains, on the other hand, are specific for a particular organism, although in some cases cross-reactions with other organisms occur. Despite the wealth of information that can be gleaned from a stained smear or section of tissue, however, the specific etiology of an infection often cannot be determined on the basis of only the morphology of the organisms seen; culture data are essential and must be considered in the final diagnosis.

Detection of infection or infectious agents by use of cytologic and histologic stains.

Among the etiologic agents of emerging infectious diseases are several bacterial organisms that naturally reside in animal and arthropod hosts. The most compelling emerging bacterial zoonotic and vector-borne diseases in the United States are Lyme disease; a Southern erythema migrans-like illness; human monocytic ehrlichiosis; human granulocytic ehrlichiosis; a novel cat flea-associated typhus group rickettsiosis; bartonelloses of immunocompetent and immunocompromised persons, particularly with AIDS; and sylvatic plague. Some of these antimicrobial-treatable infections are life threatening. During the acute stage of illness when antimicrobial agents are most effective, the flulike clinical signs and symptoms and available laboratory tests frequently do not point to a particular diagnosis. Epidemiological factors determined by the ecology of the bacteria are often the most useful diagnostic clues. The recognition of these evolving problems emphasizes the need for development of better laboratory diagnostic methods, for surveillance for and tracking of disease, and for continued research into factors contributing to transmission of the organisms. The continual appearance of previously unidentified bacterial infections requires prospective national strategies for timely recognition of the syndrome, identification of the agent, establishment of criteria and methods for diagnosis, optimization of the treatment regimen, and determination of successful approaches to prevention and control.

https://jamanetwork.com/journals/jama/articlepdf/396310/jama_275_6_039.pdf

Emerging Bacterial Zoonotic and Vector-Borne Diseases: Ecological and Epidemiological Factors

Background Rickettsialpox is caused by Rickettsia akari, which is transmitted from rodents to humans by bloodsucking mites. The initial skin lesion forms an eschar and is followed by the development of fever, malaise, myalgia, and 5 to 40 maculopapules and papulovesicles. The disease, which responds to tetracycline, can be mistaken for chickenpox. The diagnosis has been based on an increase in serum antibody titers against R. akari over a period of three to eight weeks. We discuss a more rapid technique that uses direct immunofluorescence to identify R. akari in paraffin-embedded tissue, and we describe the histopathological findings of lesional skin. Methods We studied 13 patients (age, 11 months to 58 years) who were seen at Lincoln Hospital in New York City from 1980 to 1989 and were suspected of having rickettsialpox. In nine patients serum samples were obtained during the acute and convalescent phases of the illness for indirect fluorescent-antibody testing. Punch-biopsy specimens of skin lesions wer...

Rickettsialpox in a New York city hospital, 1980 to 1989

Gouty panniculitis in a healthy male

We describe the first case of rickettsialpox in a patient infected with HIV. Immunohistochemical staining of biopsied lesions showed a relatively large number of rickettsiae within the papulovesicular rash. Rickettsialpox is easily treated and may resemble more serious cutaneous eruptions in patients infected with HIV. This diagnosis should be considered in immunocompromised city-dwellers, with fever and a papulovesicular rash.

https://www.jaad.org/article/S0190-9622(02)61469-0/pdf

James Leach

Papers

Rickettsialpox in a New York city hospital, 1980 to 1989

Gouty panniculitis in a healthy male

Rickettsialpox in a patient with HIV infection