Manifestations and Management of Flea-Borne Rickettsioses

Salivary glands of the cat flea, Ctenocephalides felis: Dissection and microscopy guide

Fleas are morphologically unique ectoparasites that are hardly mistaken for any other insect. Most flea species that feed on humans and their companion animals, including the cat flea (Ctenocephalides felis), have medical and veterinary importance. Besides facilitating blood acquisition, salivary biomolecules can modulate pathogen transmission. Thus, dissection of salivary glands is essential for comprehensive studies on disease vectors like the cat flea. Herein, we present the pictorial dissection protocol assisting future research targeting individual flea organs, for revealing their roles in vector competence and physiology. We provide a comprehensive guide, allowing researchers, even with limited practical experience, to successfully perform microdissection for collecting cat flea salivary glands. Furthermore, the protocol does not require expensive, sophisticated equipment and can be accomplished with routinely available tools. We illustrated expected results with morphological changes of salivary glands upon blood feeding as well as fluorescently stained these organs.

Case Report: Cardiovascular Manifestations due to Flea-Borne Typhus

Flea-borne typhus is a vector-borne disease caused by Rickettsia typhi that occurs worldwide, except in Antarctica. In the United States, most cases are restricted to California, Hawaii, and Texas. The syndrome is characterized by nonspecific signs and symptoms: fever, headache, rash, arthralgia, cough, hepatosplenomegaly, diarrhea, and abdominal pain. Although flea-borne typhus can cause pulmonary, neurological, and renal complications, the cardiovascular system is rarely affected. We present a case of endocarditis resulting from flea-borne typhus diagnosed by blood microbial cell-free DNA testing that required valve replacement and antibiotic therapy for 6 months. In addition, we review 20 cases of presumed and confirmed cardiovascular manifestations resulting from flea-borne typhus in the literature.

Seroprevalence of Orientia tsutsugamushi and Rickettsia typhi in water buffaloes (Bubalus bubalis) from Southern Thailand

Background and Aim

Scrub typhus and murine typhus are globally distributed zoonoses caused by the intracellular Gram-negative bacteria Orientia tsutsugamushi and Rickettsia typhi, respectively. Numerous studies have been undertaken on rickettsial illnesses in humans and animals, including arthropod vectors, in Thailand. However, the reports on the seroprevalence of antibodies to O. tsutsugamushi and R. typhi in buffaloes is extremely rare. Thus, this study aimed to estimate the seroprevalence of both rickettsial infections in water buffaloes (Bubalus bubalis) in Phatthalung Province, southern Thailand.

Materials and Methods

From February to March 2023, a total of 156 serum samples were collected from 156 water buffaloes on 29 farms in Phatthalung province. The sera were screened for antibodies against O. tsutsugamushi and R. typhi using an indirect immunofluorescence assay.

Results

The seroprevalence of antibodies against O. tsutsugamushi and R. typhi in individual water buffaloes was 4.49% (95% confidence interval [CI]: 2.19%-8.97%) and 3.85% (95% CI: 1.77%-8.14%), respectively, whereas 31% (9/29) of the herds had buffaloes with antibodies. The number of buffaloes with scrub typhus infection and ectoparasite infestation was statistically significant (p < 0.05; odds ratio = 6.25 [95% CI: 1.19-33.33]). Intriguingly, the prevalence of scrub typhus antibodies in buffaloes that were not infested with ectoparasites was much higher than those that were.

Conclusion

This is the first report of O. tsutsugamushi and R. typhi antibodies in water buffalo sera in Southern Thailand. Two serum samples showed a high antibody titer against O. tsutsugamushi. Seroprevalence mainly occurred in non-ectoparasite-infested buffaloes, especially for O. tsutsugamushi antibodies. At the herd level, one-third of the studied farms showed seroprevalence. Additional research on the occurrence of these pathogens in vectors and in other animal reservoirs is necessary.

Is vertical transmission the only pathway for Rickettsia felis?

The genus Rickettsia encompasses several species grouped into two main clusters, Typhus and the Transitional groups. The latter group contains Rickettsia felis, an endosymbiont of several arthropods with an uncertain human pathogenicity and whose most efficient transmission mechanism described thus far is transovarial. The aim of this study was to evaluate whether this pathway exists using phylogenetic analysis and partial sequences of the 17kDa and gltA genes and comparing them with host phylogeny using the cytb region. This is the first study that evaluates the vertical transmission of R. felis. In general, both phylogenies of R. felis showed no polytomies, as suspected if this pathway was the only pathway occurring. When phylogenies of the invertebrates and the gltA of R. felis were compared for strong coevolutionary insight, intricate relationships were observed, suggesting that other transmission pathways must occur, such as horizontal transmission. Further studies are needed to determine which other transmission routes occur in hematophagous arthropods.

Moonlighting in Rickettsiales: Expanding Virulence Landscape

The order Rickettsiales includes species that cause a range of human diseases such as human granulocytic anaplasmosis (Anaplasma phagocytophilum), human monocytic ehrlichiosis (Ehrlichia chaffeensis), scrub typhus (Orientia tsutsugamushi), epidemic typhus (Rickettsia prowazekii), murine typhus (R. typhi), Mediterranean spotted fever (R. conorii), or Rocky Mountain spotted fever (R. rickettsii). These diseases are gaining a new momentum given their resurgence patterns and geographical expansion due to the overall rise in temperature and other human-induced pressure, thereby remaining a major public health concern. As obligate intracellular bacteria, Rickettsiales are characterized by their small genome sizes due to reductive evolution. Many pathogens employ moonlighting/multitasking proteins as virulence factors to interfere with multiple cellular processes, in different compartments, at different times during infection, augmenting their virulence. The utilization of this multitasking phenomenon by Rickettsiales as a strategy to maximize the use of their reduced protein repertoire is an emerging theme. Here, we provide an overview of the role of various moonlighting proteins in the pathogenicity of these species. Despite the challenges that lie ahead to determine the multiple potential faces of every single protein in Rickettsiales, the available examples anticipate this multifunctionality as an essential and intrinsic feature of these obligates and should be integrated into available moonlighting repositories.

The enigmatic biology of rickettsiae: recent advances, open questions and outlook

Rickettsiae are obligate intracellular bacteria that can cause life-threatening illnesses and are among the oldest known vector-borne pathogens. Members of this genus are extraordinarily diverse and exhibit a broad host range. To establish intracellular infection, Rickettsia species undergo complex, multistep life cycles that are encoded by heavily streamlined genomes. As a result of reductive genome evolution, rickettsiae are exquisitely tailored to their host cell environment but cannot survive extracellularly. This host-cell dependence makes for a compelling system to uncover novel host-pathogen biology, but it has also hindered experimental progress. Consequently, the molecular details of rickettsial biology and pathogenesis remain poorly understood. With recent advances in molecular biology and genetics, the field is poised to start unraveling the molecular mechanisms of these host-pathogen interactions. Here, we review recent discoveries that have shed light on key aspects of rickettsial biology. These studies have revealed that rickettsiae subvert host cells using mechanisms that are distinct from other better-studied pathogens, underscoring the great potential of the Rickettsia genus for revealing novel biology. We also highlight several open questions as promising areas for future study and discuss the path toward solving the fundamental mysteries of this neglected and emerging human pathogen.