Rickettsia is a genus of nonmotile, gram-negative, nonspore-forming, highly pleomorphic bacteria that may occur in the forms of cocci, bacilli, or threads. The genus was named after Howard Taylor Ricketts in honor of his pioneering work on tick-borne spotted fever.
Rocky Mountain spotted fever (RMSF) is a bacterial disease spread by ticks. It typically begins with a fever and headache, which is followed a few days later with the development of a rash. The rash is generally made up of small spots of bleeding and starts on the wrists and ankles. Other symptoms may include muscle pains and vomiting. Long-term complications following recovery may include hearing loss or loss of part of an arm or leg.
Ticks are parasitic arachnids of the order Ixodida. They are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. The timing of the origin of ticks is uncertain, though the oldest known tick fossils are from the Cretaceous period, around 100 million years old. Ticks are widely distributed around the world, especially in warm, humid climates.
The Ixodidae are the family of hard ticks or scale ticks, one of the three families of ticks, consisting of over 700 species. They are known as 'hard ticks' because they have a scutum or hard shield, which the other major family of ticks, the 'soft ticks' (Argasidae), lack. They are ectoparasites of a wide range of host species, and some are vectors of pathogens that can cause human disease.
Rickettsia rickettsii is a Gram-negative, intracellular, cocco-bacillus bacterium that was first discovered in 1902. Having a reduced genome, the bacterium harvests nutrients from its host cell to carry out respiration, making it an organo-heterotroph. Maintenance of its genome is carried out through vertical gene transfer where specialization of the bacterium allows it to shuttle host sugars directly into its TCA cycle.
Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. The economic impact of tick-borne diseases is considered to be substantial in humans, and tick-borne diseases are estimated to affect ~80 % of cattle worldwide. Most of these pathogens require passage through vertebrate hosts as part of their life cycle. Tick-borne infections in humans, farm animals, and companion animals are primarily associated with wildlife animal reservoirs. Many tick-borne infections in humans involve a complex cycle between wildlife animal reservoirs and tick vectors. The survival and transmission of these tick-borne viruses are closely linked to their interactions with tick vectors and host cells. These viruses are classified into different families, including Asfarviridae, Reoviridae, Rhabdoviridae, Orthomyxoviridae, Bunyaviridae, and Flaviviridae.
Orientia tsutsugamushi is a mite-borne bacterium belonging to the family Rickettsiaceae and is responsible for a disease called scrub typhus in humans. It is a natural and an obligate intracellular parasite of mites belonging to the family Trombiculidae. With a genome of only 2.0–2.7 Mb, it has the most repeated DNA sequences among bacterial genomes sequenced so far. The disease, scrub typhus, occurs when infected mite larvae accidentally bite humans. This infection can prove fatal if prompt doxycycline therapy is not started.
Amblyomma is a genus of hard ticks. Some are disease vectors, for example the Rocky Mountain spotted fever in United States or ehrlichiosis in Brazil.
Amblyomma americanum, also known as the lone star tick, the northeastern water tick, or the turkey tick, is a type of tick indigenous to much of the eastern United States and Mexico, that bites painlessly and commonly goes unnoticed, remaining attached to its host for as long as seven days until it is fully engorged with blood. It is a member of the phylum Arthropoda, class Arachnida. The adult lone star tick is sexually dimorphic, named for a silvery-white, star-shaped spot or "lone star" present near the center of the posterior portion of the adult female shield (scutum); adult males conversely have varied white streaks or spots around the margins of their shields.
African tick bite fever (ATBF) is a bacterial infection spread by the bite of a tick. Symptoms may include fever, headache, muscle pain, and a rash. At the site of the bite there is typically a red skin sore with a dark center. The onset of symptoms usually occurs 4–10 days after the bite. Complications are rare but may include joint inflammation. Some people do not develop symptoms.
Rickettsia parkeri is a gram-negative intracellular bacterium. The organism is found in the Western Hemisphere and is transmitted via the bite of hard ticks of the genus Amblyomma. R. parkeri causes mild spotted fever disease in humans, whose most common signs and symptoms are fever, an eschar at the site of tick attachment, rash, headache, and muscle aches. Doxycycline is the most common drug used to reduce the symptoms associated with disease.
Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infection caused by Dabie bandavirus also known as the SFTS virus, first reported between late March and mid-July 2009 in rural areas of Hubei and Henan provinces in Central China.
Dabie bandavirus, also called SFTS virus, is a tick-borne virus in the genus Bandavirus in the family Phenuiviridae, order Bunyavirales. The clinical condition it caused is known as severe fever with thrombocytopenia syndrome (SFTS). SFTS is an emerging infectious disease that was first described in northeast and central China 2009 and now has also been discovered in Japan, South Korea, Vietnam and Taiwan in 2015. SFTS has a fatality rate of 12% and as high as over 30% in some areas. The major clinical symptoms of SFTS are fever, vomiting, diarrhea, multiple organ failure, thrombocytopenia, leukopenia and elevated liver enzyme levels. Another outbreak occurred in East China in the early half of 2020.
Borrelia turdi, formerly known as Borrelia turdae, is a spirochete bacterium first isolated from specimens of Ixodes tanuki. Its name refers to its reservoir, Turdus merula.
Rickettsia monacensis is a tick-borne spotted fever group Rickettsia species.
Lone star bandavirus is a highly divergent bunyavirus, which is carried and transmitted by the lone star tick, Amblyomma americanum. This is the same vector that transmits the SFTS virus, and the newly discovered Bhanja and Heartland viruses.
Amblyomma triguttatum, commonly known as the ornate kangaroo tick, is a species of tick in the genus Amblyomma native to Australia, in Western Australia, parts of Queensland, and in New South Wales.
Amblyomma integrum is a hard-bodied tick of the genus Amblyomma. It is found in India and Sri Lanka. Adults parasitize various larger mammals such as buffalo and cattle, whereas nymphs and larvae use mostly larger and medium mammals. In Sri Lanka, tick was identified as an agent of human otoacariasis.
Haemaphysalis hystricis, the East Asian mountain haemaphysalid, is a hard-bodied tick of the genus Haemaphysalis. It is found in India, Sri Lanka, Vietnam, Myanmar, China, Japan, India, Indonesia, Laos, Taiwan and Thailand. It is an obligate ectoparasite of mammals. It is a potential vector of Kyasanur Forest disease virus, Coxiella sp., Ehrlichia sp., and Rickettsia japonica. In 2007, an unknown trypanosoma species known as Trypanosoma KG1 isolate was isolated from naturally infected H. hystricis ticks.
