''Theileria parva'' is a species of parasites, named in honour of

Arnold Theiler Sir Arnold Theiler KCMG (26 March 1867 – 24 July 1936) Pour le Mérite is considered to be the father of veterinary science in South Africa. He was born in Frick, Canton Aargau, Switzerland. He received his higher education, and later qu ...

, that causes

East Coast fever East Coast fever, also known as theileriosis, is a disease of cattle which occurs in Africa and is caused by the protozoan parasite '' Theileria parva''. The primary vector which spreads ''T. parva'' between cattle is a tick, '' Rhipicephalus ap ...

(theileriosis) in cattle, a costly disease in Africa. The main

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 ...

for ''T. parva'' is the

tick Ticks (order Ixodida) are parasitic arachnids that 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 ...

Rhipicephalus appendiculatus ''Rhipicephalus appendiculatus'', the brown ear tick, is a hard tick found in Africa where it spreads the parasite ''Theileria parva'', the cause of East Coast fever East Coast fever, also known as theileriosis, is a disease of cattle which o ...

''. Theiler found that East Coast fever was not the same as redwater, but caused by a different protozoan.

Life cycle

Sporozoites from the tick secrete into the feeding site of the animal. Sporozoites enter lymphoblasts to form a schizont. There is a clonal expansion of schizonts and then multiply by merging to form merozoites. The merozoites go into erythrocytes and invade the cells and are now in the piroplasm stage. When a tick ingests the piroplasms, the parasites undergo syngamy in the gut and can move to hemolymph. The motile kinetes can infect the salivary glands. From this, sporogony occurs to create sporozoites to continue the life cycle.

In definitive host

In the cattle host ''T. parva'' is an intracellular parasite. Hullinger et al 1964, von Schubert et al 2010 and Woods et al 2013 find the parasite to place itself close to the

spindle apparatus In cell biology, the spindle apparatus refers to the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells. It is referred to as the mitotic spindle during mitosis, a p ...

during mitosis. This position allows it to follow the spindle through into the next generation of cells.

Genetics

The

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 g ...

was sequenced by Gardner et al 2005, finding just over 4,000 resulting

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

s. Analysis performed by Bishop et al 2005 shows at least of those are expressed during or prior to

schizont Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...

. Bishop also contains a cell study using ''T. parva''-specific

immune cell White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multi ...

s to identify

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune respons ...

Signs and symptoms

''Theileria parva'' causes East Coast fever which results from infected lymphocytes. East Coast fever has symptoms of

anorexia Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gre ...

fever Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...

, enlarged lymph nodes which can cause lymphadenopathy. Less common symptoms include diarrhea and nasal discharge. A disorder called "turning sickness" can occur and is when the parasites in cells block the blood vessels in the brain and causes brain damage. This disease usually results in death but is very uncommon.

Diagnosis

Xenodiagnosis can be used to confirm the tick vectors but is not used routinely. Blood smears can be performed to detect ''Theileria'' but can be hard to differentiate from other species. Serological assays, including indirect fluorescent antibody test, IFAT, and enzyme-linked immunosorbent assays, ELISA, are being used in research. For IFAT test, schizont or piroplasms are used from infected animals to identify transforming parasites. This method is economically friendly but is hard to differentiate between ''Theileria parva'' and other close species. ELISA is able to detect more specific antigens. Molecular assays such as PCR are continuing on the rise to be used but require more specialized equipment.

Treatment and control

Parvaquone and buparvaquone are used for the early stages of the disease and are very effective. As the disease progress, treatment is much harder to control and parvaquone and buparvaquone are less effective. Immunization for ''Theileria parva'' is available and consist of strains of ''Theileria'' from infected ticks with oxytetracycline, a type of antibiotic. This inhibits the parasite to develop. It is recommended to immunize cattle approximately 3-4 weeks before turning cattle out on to infected pasture.

Genomics

''Theileria parva'' has four chromosomes and a

plastome Chloroplast DNA (cpDNA) is the DNA located in chloroplasts, which are photosynthetic organelles located within the cells of some eukaryotic organisms. Chloroplasts, like other types of plastid, contain a genome separate from that in the cell n ...

. In 2005 the sequencing of its

was announced. ''T. parva'' has genes that allow it to attach to white blood cell (leukocyte) membranes, enter the cells and take them over. It then activates the host cells' mitotic pathway, and multiplies along with the host cells. When the genome of ''

Babesia bovis ''Babesia bovis'' is an Apicomplexan single-celled parasite of cattle which occasionally infects humans. The disease it and other members of the genus ''Babesia'' cause is a hemolytic anemia known as babesiosis and colloquially called Texas catt ...

'', another protozoan parasite that infects red blood cells (erythrocytes) and causes

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 ...

(Redwater) in cattle, was sequenced in 2007 their genomes were found to be remarkably similar.

Future outlook

Research is being done to create a more effective vaccine for ''Theileria parva''. Approximately 70% of cattle provided with the immunization were protected in a laboratory study. Research is being done to create a vaccine with a mixture of many antigens from sporozoite and schizont stage to increase immunity.

References

{{Taxonbar, from=Q7777788 Piroplasmida Parasites of mammals