Sylvatic Typhus Associated with Flying Squirrels (Glaucomys volans) in New York State, United States

Spotted Fever and Typhus Group Rickettsiae in Dogs and Humans, Mexico, 2022

We found serologic evidence of spotted fever group Rickettsia in humans and dogs and typhus group Rickettsia in dogs in Reynosa, Mexico. Our investigation revealed serologic samples reactive to spotted fever group Rickettsia in 5 community members, which highlights a potential rickettsial transmission scenario in this region.

The Rickettsioses: A Practical Update

Rickettsia are small, obligately intracellular, gram-negative bacilli. They are distributed among a variety of hematophagous arthropod vectors and cause illness throughout the world. Rickettsioses present as an acute undifferentiated febrile illness and are often accompanied by headache, myalgias, and malaise. Cutaneous manifestations include rash and eschar, which both occur at varying incidence depending on the infecting species. Serology is the mainstay of diagnosis, and the indirect immunofluorescence assay is the test of choice. Reactive antibodies are seldom present during early illness, so testing should be performed on both acute-phase and convalescent-phase sera. Doxycycline is the treatment of choice.

Emerging and re-emerging rickettsial infections

Rickettsial organisms are a diverse group of obligate intracellular bacteria; all species known to cause human disease are dependent on an arthropod vector and many are considered zoonotic diseases. Typical vectors of rickettsia are fleas, ticks, mites or lice. Humans become infected either when bitten or upon contact of broken skin or mucous membranes by infected secretions from an arthropod vector. The emergence and re-emergence of rickettsial diseases is a serious public health concern in the United States and abroad. Herein, the clinical and pathologic features of rickettsial diseases are described in tandem with the current scientific underpinnings. The histopathology of emerging and re-emerging rickettsiosis with species-specific discussion relating to vector issues and control are explored. Concepts of endemicity are addressed in the context of climate change and its impact on vector and sylvatic reservoirs, underscoring the need for clinical vigilance and broad consideration for encounters with these potentially life threating human pathogens.

Suspected and Confirmed Vector-Borne Rickettsioses of North America Associated with Human Diseases

The identification of pathogenic rickettsial agents has expanded over the last two decades. In North America, the majority of human cases are caused by tick-borne rickettsioses but rickettsiae transmitted by lice, fleas, mites and other arthropods are also responsible for clinical disease. Symptoms are generally nonspecific or mimic other infectious diseases; therefore, diagnosis and treatment may be delayed. While infection with most rickettsioses is relatively mild, delayed diagnosis and treatment may lead to increased morbidity and mortality. This review will discuss the ecology, epidemiology and public health importance of suspected and confirmed vector-transmitted Rickettsia species of North America associated with human diseases.

Fluorescence Activated Cell Sorting of Rickettsia prowazekii-Infected Host Cells Based on Bacterial Burden and Early Detection of Fluorescent Rickettsial Transformants

Rickettsia prowazekii, the causative agent of epidemic typhus, is an obligate intracellular bacterium that replicates only within the cytosol of a eukaryotic host cell. Despite the barriers to genetic manipulation that such a life style creates, rickettsial mutants have been generated by transposon insertion as well as by homologous recombination mechanisms. However, progress is hampered by the length of time required to identify and isolate R. prowazekii transformants. To reduce the time required and variability associated with propagation and harvesting of rickettsiae for each transformation experiment, characterized frozen stocks were used to generate electrocompetent rickettsiae. Transformation experiments employing these rickettsiae established that fluorescent rickettsial populations could be identified using a fluorescence activated cell sorter within one week following electroporation. Early detection was improved with increasing amounts of transforming DNA. In addition, we demonstrate that heterogeneous populations of rickettsiae-infected cells can be sorted into distinct sub-populations based on the number of rickettsiae per cell. Together our data suggest the combination of fluorescent reporters and cell sorting represent an important technical advance that will facilitate isolation of distinct R. prowazekii mutants and allow for closer examination of the effects of infection on host cells at various infectious burdens.