Professor of Veterinary Medicine, School of Veterinary Medicine, Hebrew University, Rehovot, Israel
Borrelia are spirochete bacteria transmitted by arthropod vectors. The Borrelia species can be divided into 2 major groups, Lyme Disease Borrelia which include Borrelia burgdorferi and other closely related species, and Relapsing Fever (RF) Borrelia. RF in humans is an acute infectious disease. It is characterized by recurrent episodes of fever which often concur with spirochetemia. The RF borrelioses can be grouped into two forms: louse-borne epidemic RF caused by B. recurrentis and tick-borne endemic RF transmitted by Argasid soft ticks and caused by several Borrelia spp. including B. crocidurae, B. duttoni, B. hermsii, B. hispanica and B. persica.
Infection of humans with B. persica in the Middle East is known as Persian RF and has been reported also from Iran, Egypt, Kashmir, parts of the former USSR, and western China. B. persica is transmitted by the soft tick Ornithodoros tholozoni, whose distribution includes the Middle East, central Asia and northern India. O. tholozani feeds on warm-blooded animals and commonly lives in caves, rock crevices and man-made shelters, where livestock is housed.
Microscopic examination of blood smears from two cats and a dog whose blood was submitted for a complete blood count (CBC) to a veterinary diagnostic laboratory in Israel during 2003 revealed spirochetemia. EDTA-anticoagulated blood samples from these animals were further analyzed by molecular genotyping. A one-year-old male and a two-year-old female domestic shorthair cats from the Jerusalem area were admitted to veterinary care by separate owners and at different dates due to lethargy and loss of appetite. Both of them had normal body temperatures, however, CBC revealed thrombocytopenia and severe anemia with hematocrits of 17.0% and 20.8%, respectively. Heparinized blood from the male cat was sent to the University of Leipzig in Germany in attempt to cultivate Borrelia. This cat died on the evening of admission despite antibiotic therapy with an amoxicillin-clauvolonic acid injection, whereas the female cat recovered with clearance of spirochetemia one day following treatment with the same antibiotic. A one-year-old Siberian Husky dog from a village in northern Israel was examined because of lethargy and loss of appetite. The dog was febrile with a body temperature of 40.8°C (canine normal range 37.5-39.5°C), had thrombocytopenia and anemia with a hematocrit of 27.1% (canine reference range 35-55%). It recovered following oral antibiotic treatment with ciprofloxacin for 5 days.
Blood samples from 6 febrile human RF patients that were laboratory-confirmed with Borrelia spirochetemia by microscopy of thick blood smears were collected for molecular diagnosis and genotyping. All these patients recovered following treatment with doxycycline.
Molecular Biologic Analyses and Isolation
Polymerase chain reaction (PCR) for a fragment of the Borrelia 16S rRNA gene was positive in the blood samples of all animals and of the 6 infected humans. Partial sequencing and phylogenetic analysis of the 16S rRNA sequences indicated that they were most closely related to the 16S rRNA of B. persica originating from an O. tholozani tick in Iran (GenBank accession number U42297). Additional PCR amplifications of the Borrelia flagellin (fla) and glycerophosphodiester phosphodiesterase (GlpQ) genes yielded partial gene sequences with a high degree of similarity to the canine, feline and human samples. The GlpQ gene is specific for RF Borrelia spp. and is not found in Lyme disease Borrelia.
Culture of the male cat's blood was successful with motile dividing organisms observed 9 days after seeding of the sample. Isolates were cryopreserved and passaged multiple times. Analysis of a fragment of its 16S rRNA gene indicated that it was closely related to B. persica (GenBank accession no. U42297). Isolation and in-vitro maintenance of B. presica has not been reported from vertebrates to date.
This study provides evidence that RF occurs in domestic pets in the Middle East. Interestingly, a different Borrelia sp. in North America, B. turicatae, is a causative agent of human RF that was recently described as a pathogen of dogs in Florida and Texas. These findings highlight the pathogenic potential of RF Borrelia spp. in animals.
The high identity scores and the close clustering of the 16S rRNA DNA sequences from the humans and animals in Israel with the Iranian B. persica sequence strongly support the hypothesis that B. persica is the cause of infection. However, this does not preclude the possibility that more than one RF spp. may be present in Israel or neighboring Middle Eastern countries. Since this is the first report of suspected B. persica RF in domestic animals, these findings indicate that this RF infection found in humans and animals in the same region fits the term zoonosis which relates to a disease of animals transmissible to humans or in a broader sense, any disease shared by humans and other vertebrate animals.
Although Lyme borreliosis is not endemic to Israel or the Middle East, 10% of the dogs naturally exposed to ticks were serologically positive to B. burgdorferi antigen in a study from Israel. Western blot analysis of the sera indicated that these infections cannot be attributed to B. burgdorferi sensu lato sp. but to a different cross-reactive Borrelia spp., which might have been a RF Borrelia. Further research is warranted to further elucidate the epidemiology of this infection.
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