Flying squirrel-associated Rickettsia prowazekii (epidemic typhus rickettsiae) characterized by a specific DNA fragment produced by restriction endonuclease digestion

Genotypic comparison of five isolates of Rickettsia prowazekii by multilocus sequence typing

Genetic traits of five Rickettsia prowazekii isolates, including the first from Africa and North America, and representatives from human and flying squirrels were compared using multilocus sequence typing. Four rickettsial genes encoding 17 kDa genus-common antigen (17 kDa gene), citrate synthase (gltA), OmpB immunodominant antigen (ompB) and 120 kDa cytoplasmic antigen (sca4) were examined. Sequence identities of 17 kDa gene and gltA were 100% among the isolates. Limited sequence diversity of ompB (0.02-0.11%) and sca4 (0.03-0.20%) was enough to distinguish the isolates, and evaluation of the combined four genes provided a method to easily differentiate R. prowazekii from other rickettsiae.

Real-time PCR duplex assay for Rickettsia prowazekii and Borrelia recurrentis

Rickettsia prowazekii, the etiologic agent for epidemic typhus, and Borrelia recurrentis, the etiologic agent of relapsing fever, both utilize the same vector, the human body louse (Pediculus humanus), to transmit human disease. We have developed an assay to detect both bacterial pathogens in a single tube utilizing real-time PCR. Assays for both agents are specific. The R. prowazekii and B. recurrentis assays do not detect nucleic acid from R. typhi, R. canada, or any of eight spotted fever rickettsiae. In addition they did not react with Neorickettsia risticii, N. sennetsu, Franciscella persica, Bartonella quintana, Legionella pneumophila, Proteus mirabilis, Salmonella enterica, Escherichia coli, and Staphylococcus aureus. Moreover, the B. recurrentis assay did not detect B. duttonii, B. coriaceae, B. afzelii, B. garinii, B. hermsii, or B. burgdorferi nucleic acid. Both assays detected repeatedly only R. prowazekii or B. recurrentis either when tested alone or together in one test tube.

Rickettsioses as paradigms of new or emerging infectious diseases

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.

An Anaplasma centrale DNA probe that differentiates between Anaplasma ovis and Anaplasma marginale DNA

An Anaplasma centrale genomic library was constructed in pUC13. Two clones pAC5 and pAC137 hybridising to A. centrale and A. marginale DNA were isolated from this library. One of these, pAC5, also hybridised to DNA from A. ovis. The total insert of pAC5 was subcloned into pBR322. This subclone, pAC5-12, could detect 1 ng A. centrale, 0.5 ng A. marginale and 3.9 ng A. ovis DNA. The hybridisation pattern obtained with pAC5-12 on digests of A. centrale, A. marginale and A. ovis DNA suggests that this probe detects EcoR1 and Hind111-polymorphisms. Probe pAC5-12 could detect A. ovis DNA in 36% of blood samples tested compared to the 33% detectability obtained with microscopy.

Molecular biology of rickettsiae

Our understanding of the biology of the rickettsiae, organisms that are the archetype of the obligate intracytoplasmic bacterial parasites, remains muddy and fragmentary. For example although we all appreciate that the rickettsiae can exploit their unique environment, the host cell cytoplasm, but are unable to grow axenically, the basis of this fact is still one of microbiology's central mysteries. It is unfortunate, but true, that because of the inherent difficulty of working within this system, progress on the answers to such questions will be slow and laborious. However, with the application of molecular biological methods, that is, the powerful modern approaches of genetics and biochemistry, the rickettsiology community has the realistic prospect that this field is far from being at a stand-still and that significant increases in our comprehension of the fundamental problems of rickettsial biology are occurring and will continue to occur at ever accelerating rates. Some examples, both in terms of scientific conclusions and technical approaches, of the progress made in recent years and expectations for the near future will be presented.

Genotypic identification of rickettsiae and estimation of intraspecies sequence divergence for portions of two rickettsial genes

DNA sequences from specific genes, amplified by the polymerase chain reaction technique, were used as substrata for nonisotopic restriction endonuclease fragment length polymorphism differentiation of rickettsial species and genotypes. The products amplified using a single pair of oligonucleotide primers (derived from a rickettsial citrate synthase gene sequence) and cleaved with restriction endonucleases were used to differentiate almost all recognized species of rickettsiae. A second set of primers was used for differentiation of all recognized species of closely related spotted fever group rickettsiae. The procedure circumvents many technical obstacles previously associated with identification of rickettsial species. Multiple amplified DNA digest patterns were used to estimate the intraspecies nucleotide sequence divergence for the genes coding for rickettsial citrate synthase and a large antigen-coding gene of the spotted fever group rickettsiae. The estimated relationships deduced from these genotypic data correlate reasonably well with established rickettsial taxonomic schemes.

Approaches to the molecular epidemiology of rickettsioses

This review deals with the developments of molecular approaches to the investigation of rickettsial disease epidemiology. The data presented include changes in the incidence and geographic distribution of endemic rickettsioses. Use of the DNA restriction enzyme technique, in combination with DNA probe analysis, for the molecular genetic differentiation of tick spotted fever--and typhus fever--group rickettsiae and correlation between with the analysis of polypeptide composition of the above group of rickettsiae are discussed. The data are presented on progress in the identification of various Coxiella burnetii strains as a result of restriction analysis of plasmid DNA as well as chromosomal DNA in combination with DNA probe. New and detailed characteristics of classified and newly isolated strains of rickettsiae and Coxiella burnetii revealed by molecular genetic differentiation techniques are discussed. New identification techniques using DNA probes in combination with restriction analysis of chromosomal from rickettsiae and both plasmid and chromosomal DNA from Coxiella burnetii are considered to have good prospects for future use in epidemiological assessment. The establishment of reference file banks containing restriction endonuclease data on the available typical and atypical strains of rickettsiae and Coxiella burnetii is suggested.

Flying squirrels and their ectoparasites: Disseminators of epidemic typhus

Information gathered during the past decade indicates that the eastern flying squirrel, Glaucomys volans, is a zoonotic reservoir of Rickettsia prowazekii - causative agent of louse-borne (epidemic) typhus. The sporadic cases o f typhus that have occurred in the USA in association with flying squirrels provide evidence that flying squirrels can transmit R. prowazekii infection to humons. Strains of R. prowazekii, isolated from flying squirrels multiply readily in human body lice, but flying squirrel lice, although readily infected, are very host specific and tend not to bite humans. It may be that the infection is spread to humans in infective ectoporasite faeces aerosolized when the flying squirrels groom themselves. As Joseph McDade emphasizes in this article, current concepts of typhus epidemiology and control must be re-evaluated to take into account this zoonotic aspect.