Borrelia miyamotoi
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''Borrelia miyamotoi'' is a
bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
of the
spirochete A spirochaete () or spirochete is a member of the phylum Spirochaetota (), (synonym Spirochaetes) which contains distinctive diderm (double-membrane) gram-negative bacteria, most of which have long, helically coiled (corkscrew-shaped or s ...
phylum in the genus ''
Borrelia ''Borrelia'' is a genus of bacteria of the spirochete phylum. Several species cause Lyme disease, also called Lyme borreliosis, a zoonotic, vector-borne disease transmitted by ticks. Other species of ''Borrelia'' cause relapsing fever, and are t ...
''. A
zoonotic A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...
organism, ''B. miyamotoi'' can infect humans through the bite of several species of hard-shell ''
Ixodes ''Ixodes'' is a genus of hard-bodied ticks (family Ixodidae). It includes important disease vectors of animals and humans ( tick-borne disease), and some species (notably '' Ixodes holocyclus'') inject toxins that can cause paralysis. Som ...
'' ticks, the same kind of ticks that spread ''B. burgdorferi'', the causative bacterium of
Lyme disease Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by the ''Borrelia'' bacterium, which is spread by ticks in the genus ''Ixodes''. The most common sign of infection is an expanding red rash, known as erythema migran ...
. Ixodes ticks are also the primary
vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...
in the spread of
babesiosis Babesiosis or piroplasmosis is a malaria-like parasitic disease caused by infection with a eukaryotic parasite in the order Piroplasmida, typically a ''Babesia'' or '' Theileria'', in the phylum Apicomplexa. Human babesiosis transmission via ...
and
anaplasmosis Anaplasmosis is a tick-borne disease affecting ruminants, dogs, and horses, and is caused by ''Anaplasma'' bacteria. Anaplasmosis is an infectious but not contagious disease. Anaplasmosis can be transmitted through mechanical and biological vector ...
. ''B. miyamotoi'' causes ''Borrelia miyamotoi'' disease (BMD) in humans. BMD is a
relapsing fever Relapsing fever is a vector-borne disease caused by infection with certain bacteria in the genus '' Borrelia'', which is transmitted through the bites of lice or soft-bodied ticks (genus ''Ornithodoros''). Signs and symptoms Most people who ar ...
illness that has been reported across the world, often in the same geographic areas where Lyme disease is endemic. Treatment currently follows that of Lyme disease.


Microbiology


History and morphology

''B. miyamotoi'' was discovered in 1995 when it was isolated from a population of '' Ixodes persulcates'' ticks on the
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
ese island of
Hokkaido is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The la ...
. The organism was named for Kenji Miyamoto, who initially discovered ''Borrellia'' spirochetes in Japan. It was first detected in the United States in 2001. ''B. miyamotoi'' is a
gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...
,
anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...
, obligate parasitic bacterium with a spiraling corkscrew shape.


Genetics

The bacterial
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
is physically made up of one linear
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
, twelve linear
plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...
s, and two circular plasmids, which encode a total of 1362
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
s. Four distinct
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
s of ''B. miyamotoi'' have been demonstrated based on examples isolated from Asia, Europe, and North America. ''Borrelia'' species that cause human disease are classified into two genetic
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
s, the Lyme borreliosis (LB) clade, and the relapsing fever (RF) clade. ''B. miyamotoi'' is a member of the relapsing fever (RF) clade. The ''glpQ'' gene and its resulting GlpQ protein are conserved in the RF clade of ''Borrelia'', which makes it possible to distinguish them from LB group ''Borrellia'' in testing.


Transmission

Unlike ''B. burgdoferi'', ''B. miyamotoi'' exhibits
transovarial transmission Transovarial or transovarian transmission (transmission from parent to offspring via the ovaries) occurs in certain arthropod vectors as they transmit pathogens from parent to offspring. This process, used by a wide variety of parasites, is also kn ...
, whereby the bacterium is passed from an adult tick directly into the eggs of new larvae within the ovaries. This mode of transmission has implications for diagnosis of disease because a very small larva can attach to a human host and go undetected.


Virulence factors

''B. myomotoi'' employs
antigenic variation Antigenic variation or antigenic alteration refers to the mechanism by which an infectious agent such as a protozoan, bacterium or virus alters the proteins or carbohydrates on its surface and thus avoids a host immune response, making it one of ...
and variable membrane proteins (VMPs) that help it to evade the human immune system. It is also known to evade components of the
complement cascade The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and ...
, part of
innate immune system The innate, or nonspecific, immune system is one of the two main immunity strategies (the other being the adaptive immune system) in vertebrates. The innate immune system is an older evolutionary defense strategy, relatively speaking, and is the ...
, which mounts the initial response to an infection.


Disease


History

''Borellia miyamotoi'' disease (BMD) in humans was first described in Russia in 2011, then subsequently in Japan, China, North America, Western Europe, and Asia.


Reservoirs

Several variations of
mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
and
vole Voles are small rodents that are relatives of lemmings and hamsters, but with a stouter body; a longer, hairy tail; a slightly rounder head; smaller eyes and ears; and differently formed molars (high-crowned with angular cusps instead of low-c ...
s are known rodent reservoirs for ''B. miyamotoi'', including ''
Apodemus ''Apodemus'' is a genus of Muridae (true mice and rats). The name is unrelated to that of the '' Mus'' genus, instead being derived from the Greek ἀπό-δημος (literally ''away from home''). Taxonomy Related to the Ryūkyū spiny rat ...
''
spp. In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate se ...
, ''Myodes glareolus'', and ''Peromyscus leucopus''. There is also some preliminary evidence for various avian and several large animal reservoirs such as wild boar and deer.


Vector

The primary vector for ''B. miyamotoi'' transmission is the hard-shell ''
Ixodes ''Ixodes'' is a genus of hard-bodied ticks (family Ixodidae). It includes important disease vectors of animals and humans ( tick-borne disease), and some species (notably '' Ixodes holocyclus'') inject toxins that can cause paralysis. Som ...
'' tick. Specific species of the tick have been identified in different parts of the world.


Clinical presentation

BMD presents approximately two weeks after infection with non-specific
flu-like symptoms Influenza-like illness (ILI), also known as flu-like syndrome or flu-like symptoms, is a medical diagnosis of possible influenza or other illness causing a set of common symptoms. These include fever, shivering, chills, malaise, dry cough, loss ...
including a relapsing-remitting fever in excess of 40C (104F), malaise, myalgias (muscle pain), arthralgias (joint pain), nausea, vomiting, and headache. Some patients may have elevated liver transaminases, thrombocytopenia, and leukopenia. Cases involving an
erythema migrans Erythema migrans or erythema chronicum migrans is an expanding rash often seen in the early stage of Lyme disease, and can also (but less commonly) be caused by southern tick-associated rash illness (STARI). Page last reviewed: October 22, 2015 ...
rash, which is a classic feature of Lyme disease, have been reported, but are believed to likely be the result of co-infection with ''B. burgdorfer''i and the development of co-morbid Lyme disease. ''B. miyamotoi'' has also demonstrated a slower onset neurological syndrome including meningitis in some immunocompromised patients. Since ticks in all phases of their life cycle, including very small larvae, can transmit the disease to humans, the bite and tick can easily go undetected. ''B. miyamotoi'' also transmits faster than ''B. burgdorfi'', often within 24 hours of tick attachment.


Diagnosis

No widely available diagnostic test made specifically for ''B. miyamotoi'' exists currently.
Polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) t ...
(PCR) testing for the 16S
ribosomal DNA Ribosomal DNA (rDNA) is a DNA sequence that codes for ribosomal RNA. These sequences regulate transcription initiation and amplification, and contain both transcribed and non-transcribed spacer segments. In the human genome there are 5 chromos ...
, ''fla,'' or p66 genes have been used in specialized labs. PCR for the glpQ gene can be used to rule out Lyme disease since LB clade Borrelia species don't contain it, however a positive test doesn't necessarily indicate ''B. miyamotoi'' infection because the gene exists in all RF clade ''Borrelia'' species. An investigational method of detection involving combined serologic testing for
IgG Immunoglobulin G (Ig G) is a type of antibody. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. IgG molecules are created and released by plasma B cells. Each IgG ...
and
IgM Immunoglobulin M (IgM) is one of several isotypes of antibody (also known as immunoglobulin) that are produced by vertebrates. IgM is the largest antibody, and it is the first antibody to appear in the response to initial exposure to an antig ...
antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
against both the GlpQ and VMP proteins has recently shown high sensitivity and specificity.


Treatment

No specific evidence-based treatment regimen or protocol currently exists for BMD. Treatments in use are currently similar to those used in Lyme disease. Courses of doxycycline or ceftriaxone have been reported as effective. A general resistance to amoxicillin was noted in one study. The Jarisch-Herxheimer reaction has been noted at the start of antibiotic treatment for BMD.


References


External links


CDC - Borrelia miyamotoi Disease
{{Taxonbar, from=Q3330965 miyamotoi Bacteria described in 1995