Difference between revisions of "Piroplasmida"

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==Introduction==
 
 
 
The '''piroplasms''' are a group of blood-bourne protozoa which are transmitted by [[Suborder: Metastigmata, ticks|ticks]]. The two species most of veterinary importance are ''Babesia'', ''Cytauxzoon'' and ''Theileria''.
 
 
 
Piroplasms are apicomplexan protozoa which inhabit [[Erythrocytes - WikiBlood|erythrocytes]], and sometimes other cells of vertebrates, but do not form pigment from haemoglobin. All piroplasms are small and round or pear-shaped (erythrocyte forms) and are parasitic on fish, amphibians, birds and mammals.
 
 
 
==''Babesia''==
 
[[Image:Babesia Life Cycle.jpg|thumb|right|150px|''Babesia'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
 
[[Image:Alternative Babesia life cycle diagram.jpg|thumb|right|150px|''Babesia'' Life Cycle - Mariana Ruiz Villarreal]]
 
*Infects a wide range of host species in different areas of the world
 
 
 
*Babesiosis has severe effects on cattle production in parts of the world
 
**Prevents European breeds from being successful in tropical regions where [[Suborder: Metastigmata, ticks|ticks]] are endemic.
 
**Occurs sporadically in the UK and Ireland causing losses of around £8 million per year
 
 
 
'''Life Cycle'''
 
*Both [[Suborder: Metastigmata, ticks#Disease Transmission|trans-stadial]] and [[Suborder: Metastigmata, ticks#Disease Transmission|trans-ovarian]] occurs
 
 
 
*Each female [[Suborder: Metastigmata, ticks|tick]] produces 3000 eggs
 
 
 
*The [[Suborder: Metastigmata, ticks|tick]] is the definitive host
 
 
 
*''Babesia'' multiplies in the red blood cells by '''budding'''
 
**Forms 2-4 daughter cells (species dependent)
 
**Giemsa blood smears can differentiate between species using 'Diffquik' stain
 
 
 
*''Babesia'' species are either small or large depending on the size of the daughter cells
 
 
 
*Small ''Babesia''
 
**E.g. ''B. divergens''
 
**E.g. ''B. gibsoni''
 
**Peripheral nucleus
 
**Obtuse angle
 
 
 
*Large ''Babesia''
 
**E.g. ''B. major''
 
**E.g. ''B. canis-complex''
 
**Central nucleus
 
**Acute angle
 
 
 
*Daughter cells disrupt the red blood cell and are released
 
**Spread and infect other red blood cells
 
 
 
*Antigen is released which absorbs onto other red blood cells
 
**Causes haemolysis and [[General Pathology - Pigmentation and Calcification#Haemoglobin|haemoglobin pigmentation]]
 
**Causes haemolytic anaemia, haemoglobinuria and fever
 
 
 
*In cattle:
 
**Sudden onset
 
**Often fatal if untreated
 
**Causes 'pipestem' faeces
 
**Clumping of red blood cells in brain capillaries can occur causing neurological signs
 
 
 
'''Epidemiology'''
 
*Determined by:
 
**Number of infected [[Suborder: Metastigmata, ticks|ticks]] seeking a blood mean ('''tick pressure''')
 
**Calves under 9 months are refractory to disease
 
***Can develop immunity if exposed without showing clinical signs
 
**Premunity developes quickly in infected cattle which causes a 'carrier state'
 
**Immunity can wane in the absense of re-infection
 
**Uninfected cattle remain susceptible
 
 
 
*Predisposing factors:
 
**Sucseptible animals introduced into an infected area
 
**Infected [[Suborder: Metastigmata, ticks|ticks]] are intorduced into a clean area
 
**Infected cattle are introduced into an area with clean [[Suborder: Metastigmata, ticks|ticks]]
 
**Temporary reduction in the [[Suborder: Metastigmata, ticks|tick]] population decreasing the transmission rate (causing enzootic instability)
 
**Infected are transported or stressed in other ways, e.g. parturition
 
 
 
*In the UK:
 
**Sporadic disease
 
**Enzootic instability
 
**Occurs mostly during the spring and autumn during periods of greatest [[Suborder: Metastigmata, ticks|tick]] activity
 
**Occurs mostly in stressed cattle under 2 years old on rough grazing
 
**''B. divergens'' the most common species
 
**[[Suborder: Metastigmata, ticks#Ixodes spp.|''Ixodes ricinus'']] is the vector
 
**[[Suborder: Metastigmata, ticks#Disease Transmission|Trans-ovarial]] transmission to the next generation occurs
 
**''B. major'' occurs in South East England but is not pathogenic
 
***Vector is [[Suborder: Metastigmata, ticks#Important Hard Ticks|''Haemaphysalis'']]
 
 
 
===Enzootic Instability===
 
*Low rate of transmission
 
 
 
*Few infected [[Suborder: Metastigmata, ticks|ticks]]
 
 
 
*Infrequent exposure
 
 
 
*Immunity wanes or is completely absent in many individuals
 
 
 
*Low levels of herd immunity
 
 
 
*'''Higher''' incidence of disease
 
 
 
===Enzootic Stability===
 
*High rate of transmission
 
 
 
*Many infected ticks
 
 
 
*Frequent exposure boosts immunity
 
 
 
*High level of herd immunity
 
 
 
*'''Lower''' incidence of disease
 
 
 
==''Theileria''==
 
[[Image:Theileria parva life cycle.jpg|thumb|right|150px|''Theileria parva'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
 
*Main species of veterinary importance is ''Theileria parva''
 
**Causes '''East Coast Fever'''
 
***Severe, proliferative lymphatic disease of cattle
 
***Central and Eastern Africa
 
***Transmitted by [[Suborder: Metastigmata, ticks#Ticks of Veterinary Importance|''Rhipicephalus appendiculatus'']]
 
***[[Suborder: Metastigmata, ticks#Disease Transmission|Trans-stadial]] transmission
 
 
 
*Other ''Theileria'' species causes production losses in cattle and sheep in the Middle East, Mediterranean and in Northern Africa
 
 
 
'''Life Cycle'''
 
*Incubation phase lasts 1 week
 
 
 
*Lymphoblast proliferation
 
**Local [[Lymph Nodes - Anatomy & Physiology|lymph node]] first infected then spreads through body
 
**Occurs in week two
 
 
 
*Lymphoid depletion
 
**[[Lymphocytes - WikiBlood|Lymphocytes]] killed
 
**Decreases lymphopoiesis
 
**Occurs in week 3
 
 
 
*Total incubation period takes about 18 days
 
 
 
'''Diagnosis'''
 
*Clinical signs
 
**Pyrexia
 
**Enlarged local [[Lymph Nodes - Anatomy & Physiology|lymph node]]
 
***Usually parotid [[Lymph Nodes - Anatomy & Physiology|lymph node]] as [[Suborder: Metastigmata, ticks#Ticks of Veterinary Importance|''Rhipicephalus appendiculatus'']] feeds in the ear
 
**Loss of condition
 
 
 
*Examine Giemsa stained smears of:
 
**Local [[Lymph Nodes - Anatomy & Physiology|lymph node]] aspirated for schizonts
 
**Blood smears for pioplasms in red blood cells
 
 
 
*Post-mortem
 
**Pulmonary oedema
 
**Gut mucosal haemorrhages
 
**[[Lymph Nodes - Anatomy & Physiology|Lymph node]] and [[Spleen - Anatomy & Physiology|spleen]] cellular atrophy
 
 
 
'''Control'''
 
*Integrated control of both the [[Suborder: Metastigmata, ticks|tick]] and vector
 
**[[Vaccines - WikiBlood|Vaccination]] and [[ectoparasiticides]]
 
 
 
*Current [[Vaccines - WikiBlood|vaccination]] is live unattentuated
 
**Contains frozen stabilate of ground up tick gut containing infective sporozoites
 
**Long lasting oxytetracycline administered at the same time to slow down schizogony giving the immune response time to develop
 
 
 
==''Cytauxzoon felis''==
 
 
 
*Cytauxzoon is classified in the order ''Piroplasmida'' and family ''Theileriidae''
 
**This family has both an erythrocytic and a tissue (leukocytic) phase
 
 
*The ''Babesiidae'', a related family, is characterized by having a primarily erythrocytic phase in the mammalian host
 
**Its morphological features are indistinguishable from the erythrocytic form of Cytauxzoon
 
 
 
*''Cytauxzoon felis'', ''B. equi'', and ''B. rodhaini'' have been linked to both the babesias and theilerias by RNA gene sequence analysis
 
**It has been suggested that these organisms be reclassified within a separate family
 
 
 
'''Life Cycle'''
 
*Large schizonts of ''C. felis'' develop in [[Macrophages - WikiBlood|macrophages]]
 
**In Theileria the exoerythrocytic stage occurs primarily within [[Lymphocytes - WikiBlood|lymphocytes]]
 
 
 
*In ''C. felis'', schizonts develop within mononuclear phagocytes, initially as indistinct vesicular structures and later as large, distinct nucleated schizonts that actively undergo division by true schizogony and binary fission
 
 
 
*Later in the course of the disease, schizonts develop buds (merozoites) that separate and eventually fill the entire host cell
 
 
*Each schizont may contain numerous merozoites
 
**Ultrastructurally, schizonts lack a parasitophorous vacuole, and individual merozoites possess rhoptries
 
 
 
*The host cell ruptures, releasing merozoites into the tissue fluid and blood
 
 
 
*Merozoites are then believed to enter erythrocytes to form the intraerythrocytic stage
 
 
*Merozoites appear in [[Macrophages - WikiBlood|macrophages]] one to three days before they are observed in [[Erythrocytes - WikiBlood|erythrocytes]]
 
 
'''Pathogenicity'''
 
*[[Suborder: Metastigmata, ticks|Ticks]] are implicated as the natural vector for ''Cytauxzoon''
 
**Most cases of infection have been associated with the presence of these parasites on the hosts
 
**Experimentally, ''Dermacentor variabilis'' can transmit the organism from bobcats to domestic cats.  In a white tiger that developed a natural, fatal infection in Florida, two female Lone Star ticks (''Amblyomma americanum'') were present on the inguinal skin. 
 
 
 
*Clinically, the disease in cats is characterized by fever, depression, dyspnea, anorexia, lymphadenopathy, anaemia, and icterus leading to death in three to six days
 
 
 
*Gross findings include pale or icteric mucous membranes, petechiae and ecchymoses in the [[Lungs - Anatomy & Physiology|lung]], [[Heart - Anatomy & Physiology|heart]], [[Lymph Nodes - Anatomy & Physiology|lymph nodes]] and on mucous membranes, splenomegaly, lymphadenomegaly, and hydropericardium
 
 
*Microscopically, numerous large schizonts are present within the cytoplasm of endothelial-associated [[Macrophages - WikiBlood|macrophages]]
 
**Infected macrophages become markedly enlarged (up to 75μm) and may occlude the lumens of numerous vessels of many tissues, especially the [[Lungs - Anatomy & Physiology|lungs]]
 
**Minimal inflammatory reaction is present in tissues
 
 
 
'''Diagnosis'''
 
*Merozoites within [[Erythrocytes - WikiBlood|erythrocytes]], best seen on peripheral blood or tissue impressions, are variable in morphology and can occur as round, oval, or signet ring-shaped bodies
 
**Are 1-5 micrometers in diameter
 
**Small, peripherally placed basophilic nucleus
 
 
 
*Organisms that must be distinguished from the intraerythrocytic phase of ''C. felis'' include ''Babesia'' and ''Hemobartonella''
 
**The blood stage may appear similar to the ring forms of ''Hemobartonella'' and to the piriforms of ''Babesia''
 
**Unlike ''Cytauxzoon'', ''babesiosis'' and ''hemobartonellosis'' do not have a tissue stage of infection
 
 
 
*Differential diagnosis for the tissue phase of ''cytauxzoonosis'' includes other small (less than 5 μm), intrahistiocytic organisms such as ''Toxoplasma'', ''Leishmania'' and ''Histoplasma''
 

Latest revision as of 22:38, 9 April 2010