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PARASITES
PROTOZOA



Babesia

Babesia Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC
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 ticks are endemic.
    • Occurs sporadically in the UK and Ireland causing losses of around £8 million per year

Life Cycle

  • Each female tick produces 3000 eggs
  • The 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 'Difquik' 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 adsorbs onto other red blood cells
  • 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 ticks seeking a blood meal (tick pressure)
    • Calves under 9 months are refractory to disease
      • Can develop immunity if exposed without showing clinical signs
    • 'Premunity' (a good protective immunity) develops quickly in infected cattle causing a 'carrier state'
    • Immunity can wane in the absence of re-infection
    • Uninfected cattle remain susceptible
  • Predisposing factors:
    • Susceptible animals introduced into an infected area
    • Infected ticks introduced into a clean area
    • Infected cattle introduced into an area with clean ticks
    • Temporary reduction in the 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 tick activity
    • Occurs mostly in stressed cattle under 2 years old on rough grazing
    • B. divergens the most common species
    • Ixodes ricinus is the vector
    • Trans-ovarial transmission to the next generation occurs
    • B. major occurs in South East England but is not pathogenic
  • Overseas
    • B. bovis causes considerable losses in cattle in many tropical and sub-tropical areas
      • In Australia an attenuated vaccine is used
      • Vector is Boophilus
    • B. bigemina causes problems in Africa and South America
  • Dogs
    • Complex epidemiology
    • Recognised species are extending their endemic ranges due to the discovery of the small Babesia species, pet passport scheme and increased overseas travel
    • Large species comprises 3 subspecies
      • B. canis canis is the most important
        • Dermacentor vector
        • Largely confined to southern Europe but is spreading
      • B. canis uses Rhipicephalus as a vector and is spreading northwards through Europe
      • B. gibsoni is now established in the USA and South-East Asia
    • British dogs have no immunity as no species are endemic to the UK so are highly susceptible if taken abroad
    • Prevention of tick bites by use of an 'Amitraz' collar is currently the best method of protection
  • Horses
    • 2 species occur
    • B. equi is the most pathogenic
    • Not endemic to the UK
    • Serology using ELISA or IFAT to diagnose
  • Sheep and goats
    • Several species
    • Little clinical significance

Enzootic Instability

  • Low rate of transmission
  • 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

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
    • In Theileria the exoerythrocytic stage occurs primarily within 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

Pathogenicity

  • 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, dyspnoea, 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 lung, heart, lymph nodes and on mucous membranes, splenomegaly, lymphadenomegaly, and hydropericardium
  • Microscopically, numerous large schizonts are present within the cytoplasm of endothelial-associated macrophages
    • Infected macrophages become markedly enlarged (up to 75μm) and may occlude the lumen of numerous vessels of many tissues, in particular the lungs
    • Minimal inflammatory reaction is present in tissues

Diagnosis

  • Merozoites within 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

Theileria

Theileria parva Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC
File:Lymph node smear East Coast Fever.jpg
Lymph node smear of a cow with East Coast Fever - Drs. Elizabeth Howerth and Bruce LeRoy, Department of Pathology, UGA College of Veterinary Medicine
File:H and E stain brain East Coast Fever.jpg
H and E stain of brain and meningal vessels of a cow with East Coast Fever - Drs. Elizabeth Howerth and Bruce LeRoy, Department of Pathology, UGA College of Veterinary Medicine
Theileria cervi (deer) - Drs. Elizabeth Howerth and Bruce LeRoy, Department of Pathology, UGA College of Veterinary Medicine
  • Main species of veterinary importance is Theileria parva
  • Other Theileria species cause 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 node first infected then spreads through body
    • Occurs in week two
  • Lymphoid depletion
    • Lymphocytes killed
    • Decreases lymphopoiesis
    • Occurs in week 3
  • Total incubation period takes about 18 days

Diagnosis

  • Examine Giemsa stained smears of:
    • Local lymph node aspirated for schizonts
    • Blood smears for piroplasms in red blood cells
  • Post-mortem

Control

  • Current 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

Piroplasmida Flashcards