Yabuuchi et al. 1993
Glanders bacillus Loeffler 1882
Burkholderia mallei is a Gram-negative, bipolar, aerobic bacterium, a human and animal pathogen of genus Burkholderia causing glanders; the Latin name of this disease (malleus) gave its name to the species causing it. It is closely related to B. pseudomallei, and by multilocus sequence typing it is a subspecies of B. pseudomallei. B. mallei evolved from B. pseudomallei by selective reduction and deletions from the B. pseudomallei genome. Unlike B. pseudomallei and other genus members, B. mallei is nonmotile; its shape is coccobacillary measuring some 1.5–3.0 μm in length and 0.5–1.0 μm in diameter with rounded ends.
Bacteria are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only about half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.
Humans are the only extant members of the subtribe Hominina. Together with chimpanzees, gorillas, and orangutans, they are part of the family Hominidae. A terrestrial animal, humans are characterized by their erect posture and bipedal locomotion; high manual dexterity and heavy tool use compared to other animals; open-ended and complex language use compared to other animal communications; larger, more complex brains than other animals; and highly advanced and organized societies.
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres (110 ft) and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal often refers only to non-human animals. The study of non-human animals is known as zoology.
Wilhelm Schütz and Friedrich Löffler first isolated B. mallei in 1882. –1909) gave the pathogen its binomial name, after analyzing samples of the bacterium. He further refined his observations with the pathogen in 1886.It was isolated from an infected liver and spleen of a horse. This bacterium is also one of the first to be identified containing a type VI secretion system which is important for its pathogenicity. In 1885, the German Botanist and Bacteriologist, Wilhelm Zopf (1846
FriedrichWilhelm Zopf was a well-known German botanist and mycologist. He dedicated to his whole life with fungal biology, particularly in classification of fungi and dye production in fungi and lichens. Besides, his textbook on fungi called “Die pilze in morphologischer, physiologischer, biologischer und systematischer beziehung ” in 1890 was also an outstanding work on the subject for many decades. Thus, his numerous contributions gave him a special status in mycological history.
Most organisms within the Burkholderiaceae live in soil; however, B. mallei does not. Because B. mallei is an obligate mammalian pathogen, it must infect a host mammal to live and to be transmitted from one host to another.
In biology, a pathogen, in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.
In biology and medicine, a host is an organism that harbours a parasitic, a mutualistic, or a commensalist guest (symbiont), the guest typically being provided with nourishment and shelter. Examples include animals playing host to parasitic worms, cells harbouring pathogenic (disease-causing) viruses, a bean plant hosting mutualistic (helpful) nitrogen-fixing bacteria. More specifically in botany, a host plant supplies food resources to micropredators, which have an evolutionarily stable relationship with their hosts similar to ectoparasitism. The host range is the collection of hosts that an organism can use as a partner.
B. mallei is very closely related to B. pseudomallei, being 99% identical in conserved genes when compared to B. pseudomallei. B. malllei has about 1.4 Mb less DNA than B. pseudomallei.B. mallei may have actually evolved from a strain of B. pseudomallei after the latter had infected an animal. The bacterium would have lost the genes that were not necessary for living in an animal host. This suggestion has found support from studies that compare strains of B. mallei to B. pseudomallei and indicate that their two respective genomes are very similar. The genes that allowed the bacterium to survive in a soil environment, like genes that gave B. mallei the capacity to protect against bactericidals, antibiotics, and antifungals, were likely deleted. Thus, the reason that B. mallei is not found outside of a host is because it lacks the genes necessary for survival in the soil. Genome comparisons also seem to indicate that the B. mallei is still evolving and adapting to an intracellular lifestyle.
Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses. DNA and ribonucleic acid (RNA) are nucleic acids; alongside proteins, lipids and complex carbohydrates (polysaccharides), nucleic acids are one of the four major types of macromolecules that are essential for all known forms of life.
In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".
The genome of B. mallei was sequenced in the United States by The Institute of Genomic Research. The size of the genome is smaller than that of B. pseudomallei. The B. mallei sequence revealed a chromosome of 3.5 mega base pairs (Mb) and a 2.3 Mb "megaplasmid”. Many insertion sequences and phase-variable genes were also found.The genome for B. mallei is made up of two circular chromosomes. Chromosome 1 is where genes relating to metabolism, capsule formation, and lipopolysaccharide biosynthesis are located. B. mallei has a polysaccharide capsule which indicates its potential as a pathogen. Chromosome 2 is where most of the information regarding secretion systems and virulence-associated genes are located. Multilocus sequence typing has revealed that B. mallei most likely evolved from a B. pseudomallei clone reduction. About 1000 B. pseudomellei genes are absent or varying in the B. mallei genome. B. mallei’s genome also has a large amount of insertion sequences.
The J. Craig Venter Institute (JCVI) is a non-profit genomics research institute founded by J. Craig Venter, Ph.D. in October 2006. The Institute was the result of consolidating four organizations: the Center for the Advancement of Genomics, The Institute for Genomic Research (TIGR), the Institute for Biological Energy Alternatives, and the J. Craig Venter Science Foundation Joint Technology Center. It has facilities in Rockville, Maryland and La Jolla, California.
A chromosome is a deoxyribonucleic acid (DNA) molecule with part or all of the genetic material (genome) of an organism. Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteins, bind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle.
A base pair (bp) is a unit consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA and RNA. Dictated by specific hydrogen bonding patterns, Watson-Crick base pairs allow the DNA helix to maintain a regular helical structure that is subtly dependent on its nucleotide sequence. The complementary nature of this based-paired structure provides a redundant copy of the genetic information encoded within each strand of DNA. The regular structure and data redundancy provided by the DNA double helix make DNA well suited to the storage of genetic information, while base-pairing between DNA and incoming nucleotides provides the mechanism through which DNA polymerase replicates DNA and RNA polymerase transcribes DNA into RNA. Many DNA-binding proteins can recognize specific base-pairing patterns that identify particular regulatory regions of genes.
B. mallei was first called "Bacillus mallei" and was in the genus Pseudomonas until the early 1990s. It has also been referred to as "farcy". It is now part of the genus Burkholderia.
No standardized system exists for differentiating between B. mallei and B. pseudomallei. The methods that have been used to differentiate and identify one strain from the other include ribotyping, pulsed-field gel electrophoresis, multilocus enzyme electrophoresis, random amplified polymorphic DNA analysis, and multilocus sequence typing.Comparing the DNA of B. mallei and B. pseudomallei must be done at the 23S rDNA level, however, since no identifiable difference is found between the two species at the 16S rDNA level.
Both B. mallei and B. pseudomallei can be cultured in a laboratory; nutrient agar can be used to grow the bacteria. When grown in culture, B. mallei grows in smooth, grey, translucent colonies. In a period of 18 hours at 37 °C, a B. mallei colony can grow to about 0.5–1.0 mm in diameter. B. mallei culture growth on MacConkey agar is variable. Many microbiologists are unfamiliar with B. mallei and as a result it has frequently been misidentified as a Pseudomonas species or as a contaminant in a culture.
The bacterium is susceptible to numerous disinfectants including benzalkonium chloride, iodine, mercuric chloride, potassium permanganate, 1% sodium hypochlorite, and ethanol. The micro-organism can also be destroyed by heating or ultraviolet light. Antibiotics such as streptomycin, amikacin, tetracycline, doxycycline, carbapenems, ceftazidime, amoxicillin/clavulanic acid, piperacillin, chloramphenicol, and sulfathiazole have been reported to be effective against the bacteria in vitro . B. mallei, like B. pseudomallei, is also resistant to a number of antibiotics including aminoglycosides, polymyxins, and beta-lactams. No vaccine is currently available for humans or animals to protect against B. mallei infection.An animal model that will predict immune responses necessary to create immunity to the bacterium is needed before a vaccine can be developed. Mice are fairly close to humans in their susceptibility to B. mallei and would be the ideal choice of animal for creating a model for the vaccine.
B. mallei is responsible for causing glanders disease, which historically mostly affected animals, such as horses, mules, and donkeys, and rarely humans. Horses are considered the natural host for B. mallei infection and are highly susceptible to it.B. mallei infects and gains access to the cell of its host through lysis of the entry vacuole. B. mallei has bacterial protein-dependent, actin-based motility once inside the cell. It is also able to initiate host cell fusion that results in multinucleated giant cells (MNGCs). The consequence of MNGCs has yet to be determined, but it may allow the bacteria to spread to different cells, evade responses by the infected host’s immune system, or allow the bacteria to remain in the host longer. B. mallei is able to survive inside host cells through its capabilities in disrupting the bacteria-killing functions of the cell. It leaves the vacuoles early, which allows for efficient replication of the bacteria inside the cell. Leaving the cell early also keeps the bacteria from being destroyed by lysosomal defensins and other pathogen-killing agents. MNGCs may help protect the bacteria from immune responses. B. mallei’s ability to live within the host cell makes developing a vaccine against it difficult and complex. The vaccine would need to create a cell-mediated immune response, as well as a humoral response to the bacteria in to be effective in protecting against B. mallei. In regards to a vaccine against B. mallei, the closeness of B. mallei to B. pseudomallei may make it possible that a vaccine developed for either type would be effective against the other.
Horses chronically infected with B. mallei with glanders disease typically experience mucus-containing nasal discharge, lung lesions, and nodules around the liver or spleen. Acute infection in horses results in a high fever, loss of fat or muscle, erosion of the surface of the nasal septum, hemorrhaging or mucus discharge. The bacterium mostly affects the lungs and airways.Human infection with B. mallei is rare, although it occasionally occurs among laboratory workers dealing with the bacteria or those who are frequently near infected animals. The bacteria usually infect a person through their eyes, nose, mouth, or cuts in the skin. Once people are infected, they develop a fever and rigors. Eventually, they get pneumonia, pustules, and abscesses, which prove fatal within a week to 10 days if left untreated by antibiotics. The way someone is infected by the bacteria also affects the type of symptoms that will result. If the bacteria enter through the skin, a local skin infection can result, while inhaling B. mallei can cause septicemic or pulmonary, muscular, hepatic, or splenous infections. B. mallei infection has a fatality rate of 95% if left untreated, and a 50% fatality rate in individuals treated with antibiotics.
In the first days of B. mallei infection, neutrophils, macrophages, and T cells go to the spleen in great quantities. The early cellular response to B. mallei infection involves Gr-1+ (antigen) cells, and implies their importance to immunity against this bacterial infection. T cells (nitric oxide) are actually more involved in combating B. mallei in the later stages of its infection of a host.
Lipopolysaccharide isolated from B. mallei demonstrated significantly lower biological activity as compared to the LPS from Escherichia coli , in agreement with the lower degree of acylation of its lipid A: the major forms of B. mallei lipid A were penta- and tetraacylated, whereas classical lipid A from E. coli was hexaacylated. In addition, lipid A from B. mallei contains 4-amino-4-deoxyarabinose residue in almost half of the molecules, which would partially neutralize the negative charge of the phosphate groups necessary for the interaction with the positively charged amino acids of TLR4. At the same time, lipid A acyl chains in B. mallei were on the average longer (14–16 carbon atoms) than those in E. coli (14 carbon atoms), yet LPS from B. mallei appeared to be a weaker activator. B. mallei may employ LPS with low biological activity to evade proper recognition by the TLR4/MD-2 complex of innate immune system, dampening the host immune response and increasing the risk of bacterial dissemination.
B. mallei has been eradicated in the United States and most Western countries, but still affects animals in Africa, Asia, the Middle East, Central America, and South America.Many Western countries were able to eliminate the disease through glanders control programs and laws requiring notification of cases of infection to health departments and the destruction of any animal affected with B. mallei.
B. mallei and B. pseudomallei have a history of being on a list of potential biological warfare agents. The Centers for Disease Control and Prevention classifies B. mallei as a category B critical biological agent.As a result, research regarding B. mallei may only be done in biosafety level 3 facilities in the US and internationally. Though it is so highly infective and a potential biological weapon, little research has been conducted on this bacterium. B. mallei and B. pseudomallei under the policy of Institutional Oversight of Life Sciences Dual Use Research of Concern would be subject to oversight to ensure the responsible investigation of these agents.
In March 2000, one of the first cases since the 1940s of glanders in the United States occurred in a young microbiologist working for the U.S. Army Medical Research Institute for Infectious Diseases. The researcher had type 1 diabetes and had been working with B. mallei for about two years, but he did not always wear gloves while conducting his research. The researcher experienced enlargement of the lymph nodes and a fever which lasted for 10 days even with antibiotic treatment. In the following weeks, the researcher experienced fatigue, rigors, night sweats, and loss of weight. The next month, his symptoms seemed to disappear after treatment with clarithromycin, but after the medication was stopped, the symptoms reappeared. After conducting multiple tests on cultures from the researcher’s blood and a biopsied portion of a liver abscess, the bacterium was identified as B. mallei. Once it was established what infected the researcher, another course of antibiotics was given (imipenem and doxycycline) with 6 months of treatment. After a year, the researcher made a full recovery.
This incident also showed how a cut or skin abrasion is not absolutely necessary to contract the disease, as the researcher had no recollection of any cut or accident while working in the laboratory. The case was significant as it showed the difficulty that microbiology laboratories have in identifying bioweapon agents and the potential consequences if measures are not taken to prepare for an actual biological attack.
B. mallei was intentionally used to infect animals and humans during World War I. The Germans used B. mallei to infect animals that were being sent from neutral countries to the Allies with glanders.The Germans' plans for biological warfare started in 1915 on the East Coast of the United States; they intended to infect and kill the livestock that were being sent to the Allies and facilitate the transfer of the disease to humans. The East Coast was where many animals were being assembled for shipment to the Allies fighting in Europe. The Germans also targeted Romania, Norway, and Spain's animal supplies with cultures of glanders. The German biological sabotage eventually spread to Argentina, where agents would rely on bacterial cultures from Spain to infect the cattle, horses, and mules that Argentina was supplying to the Allies. The German use of microbes as weapons is one of the only documented attacks of intentionally using biological weapons against neutral countries.
The Japanese used B. mallei in their biological warfare research units. The most notable and notorious unit, Unit 731, used the bacterium to conduct experiments on live human subjects. However, the Japanese did not end up creating a biological weapon out of B. mallei. They did actually use B. mallei to test its effectiveness in contaminating water supplies, and the results of these tests were successful.
The Russians' biological weapons program also took an interest in B. mallei and conducted field tests with it. Some of the researchers from the program were actually infected and killed by it during the course of their research. It has been suggested that the Russians eventually used B. mallei during their war in Afghanistan against the mujahideen .
Infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce. Infectious disease, also known as transmissible disease or communicable disease, is illness resulting from an infection.
Neisseria gonorrhoeae, also known as gonococcus (singular), or gonococci (plural) is a species of Gram-negative diplococci bacteria isolated by Albert Neisser in 1879. It causes the sexually transmitted genitourinary infection gonorrhea as well as other forms of gonococcal disease including disseminated gonococcemia, septic arthritis, and gonococcal ophthalmia neonatorum.
Neisseria is a large genus of bacteria that colonize the mucosal surfaces of many animals. Of the 11 species that colonize humans, only two are pathogens, N. meningitidis and N. gonorrhoeae. Most gonoccocal infections are asymptomatic and self-resolving, and epidemic strains of the meningococcus may be carried in >95% of a population where systemic disease occurs at <1% prevalence.
Melioidosis is an infectious disease caused by a Gram-negative bacterium, Burkholderia pseudomallei, found in soil and water. It is of public health importance in endemic areas, particularly in northeast Thailand, Vietnam, and northern Australia. It exists in acute and chronic forms. Signs and symptoms may include pain in chest, bones, or joints; cough; skin infections, lung nodules, and pneumonia.
Glanders is an infectious disease that occurs primarily in horses, mules, and donkeys. It can be contracted by other animals, such as dogs, cats, goats and humans. It is caused by infection with the bacterium Burkholderia mallei, usually by ingestion of contaminated feed or water. Signs of glanders include the formation of nodular lesions in the lungs and ulceration of the mucous membranes in the upper respiratory tract. The acute form results in coughing, fever, and the release of an infectious nasal discharge, followed by septicaemia and death within days. In the chronic form, nasal and subcutaneous nodules develop, eventually ulcerating. Death can occur within months, while survivors act as carriers.
Haemophilus influenzae is a Gram-negative, coccobacillary, facultatively anaerobic pathogenic bacterium belonging to the Pasteurellaceae family. H. influenzae was first described in 1892 by Richard Pfeiffer during an influenza pandemic.
Burkholderia is a genus of Proteobacteria whose pathogenic members include the Burkholderia cepacia complex which attacks humans and Burkholderia mallei, responsible for glanders, a disease that occurs mostly in horses and related animals; Burkholderia pseudomallei, causative agent of melioidosis; and Burkholderia cepacia, an important pathogen of pulmonary infections in people with cystic fibrosis (CF).
Francisella tularensis is a pathogenic species of Gram-negative coccobacillus, an aerobic bacterium. It is non-spore forming, non-motile and the causative agent of tularemia, the pneumonic form of which is often lethal without treatment. It is a fastidious, facultative intracellular bacterium which requires cysteine for growth. Due to its low infectious dose, ease of spread by aerosol, and high virulence, F. tularensis is classified as a Tier 1 Select Agent by the U.S. government, along with other potential agents of bioterrorism such as Yersinia pestis, Bacillus anthracis and Ebola virus. When found in nature, Francisella tularensis can survive for several weeks at low temperatures in animal carcasses, soil, and water. In laboratory, F. tularensis appears as small rods, and is grown best at 35-37°C.
Neisseria meningitidis, often referred to as meningococcus, is a Gram-negative bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life-threatening sepsis. It has also been reported to be transmitted through oral sex and cause urethritis in men. The bacterium is referred to as a coccus because it is round, and more specifically, diplococcus because of its tendency to form pairs. About 10% of adults are carriers of the bacteria in their nasopharynx. As an exclusively human pathogen it is the main cause of bacterial meningitis in children and young adults, causing developmental impairment and death in about 10% of cases. It causes the only form of bacterial meningitis known to occur epidemically, mainly Africa and Asia. It occurs worldwide in both epidemic and endemic form. N. meningitidis is spread through saliva and respiratory secretions during coughing, sneezing, kissing, chewing on toys and even through sharing a source of fresh water. It infects its host cells by sticking to them with long thin extensions called pili and the surface-exposed proteins Opa and Opc and has several virulence factors.
Adhesins are cell-surface components or appendages of bacteria that facilitate adhesion or adherence to other cells or to surfaces, usually the host they are infecting or living in. Adhesins are a type of virulence factor.
Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction. Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formations of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally. The genetic material of the bacteriophage, called a prophage, can be transmitted to daughter cells at each subsequent cell division, and at later events can release it, causing proliferation of new phages via the lytic cycle. Lysogenic cycles can also occur in eukaryotes, although the method of DNA incorporation is not fully understood.
Burkholderia pseudomallei is a Gram-negative, bipolar, aerobic, motile rod-shaped bacterium. It is a soil-dwelling bacterium endemic in tropical and subtropical regions worldwide, particularly in Thailand and northern Australia. It infects humans and animals and causes the disease melioidosis. It is also capable of infecting plants.
Viral vectors are tools commonly used by molecular biologists to deliver genetic material into cells. This process can be performed inside a living organism or in cell culture. Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect. Delivery of genes, or other genetic material, by a vector is termed transduction and the infected cells are described as transduced. Molecular biologists first harnessed this machinery in the 1970s. Paul Berg used a modified SV40 virus containing DNA from the bacteriophage λ to infect monkey kidney cells maintained in culture.
Antigenic variation refers to the mechanism by which an infectious agent such as a protozoan, bacterium or virus alters its surface proteins in order to avoid a host immune response. It is related to phase variation. Immune evasion is particularly important for organisms that target long-lived hosts, repeatedly infect a single host and are easily transmittable. Antigenic variation not only enables immune evasion by the pathogen, but also allows the microbes to cause re-infection, as their antigens are no longer recognized by the host's immune system. When an organism is exposed to a particular antigen an immune response is stimulated and antibodies are generated to target that specific antigen. The immune system will then "remember" that particular antigen, and defenses aimed at that antigen become part of the immune system’s acquired immune response. If the same pathogen tries to re-infect the same host the antibodies will act rapidly to target the pathogen for destruction. However, if the pathogen can alter its surface antigens, it can evade the host's acquired immune system. This will allow the pathogen to re-infect the host while the immune system generates new antibodies to target the newly identified antigen. Antigenic variation can occur by altering a variety of surface molecules including proteins and carbohydrates. There are many molecular mechanisms behind antigenic variation, including gene conversion, site-specific DNA inversions, hypermutation, as well as recombination of sequence cassettes. In all cases, antigenic variation and phase variation result in a heterogenic phenotype of a clonal population. Individual cells either express the phase-variable protein(s) or express one of multiple antigenic forms of the protein. This form of regulation has been identified mainly, but not exclusively, for a wide variety of surface structures in pathogens and is implicated as a virulence strategy.
Lyme disease, or borreliosis, is caused by spirochetal bacteria from the genus Borrelia, which has 52 known species. Three main species are the main causative agents of the disease in humans, while a number of others have been implicated as possibly pathogenic. Borrelia species in the species complex known to cause Lyme disease are collectively called Borrelia burgdorferisensu lato (s.l.) not to be confused with the single species in that complex Borrelia burgdorferi sensu stricto which is responsible for all cases of Lyme disease in North America.
Burkholderia thailandensis is a nonfermenting motile, Gram-negative bacillus that occurs naturally in soil. It is closely related to Burkholderia pseudomallei, but unlike B. pseudomallei, it only rarely causes disease in humans or animals. The lethal inoculum is approximately 1000 times higher than for B. pseudomallei. It is usually distinguished from B. pseudomallei by its ability to assimilate arabinose. Other differences between these species include lipopolysaccharide composition, colony morphology, and differences in metabolism.
A virus is a biological agent that reproduces inside the cells of living hosts. When infected by a virus, a host cell is forced to produce thousands of identical copies of the original virus at an extraordinary rate. Unlike most living things, viruses do not have cells that divide; new viruses are assembled in the infected host cell. But unlike still simpler infectious agents, viruses contain genes, which gives them the ability to mutate and evolve. Over 5,000 species of viruses have been discovered.
Pathogen infections are among the leading causes of infirmity and mortality among humans and other animals in the world. Until recently, it has been difficult to compile information to understand the generation of pathogen virulence factors as well as pathogen behaviour in a host environment. The study of pathogenomics attempts to utilize genomic and metagenomics data gathered from high through-put technologies, to understand microbe diversity and interaction as well as host-microbe interactions involved in disease states. The bulk of pathogenomics research concerns itself with pathogens that affect human health; however, studies also exist for plant and animal infecting microbes.
Theileria parva is a species of parasites, named in honour of Arnold Theiler, that causes East Coast fever (theileriosis) in cattle, a costly disease in Africa. The main vector for T. parva is the tick Rhipicephalus appendiculatus. Theiler found that East Coast fever was not the same as redwater, but caused by a different protozoan.