Piroplasmida

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

• Both trans-stadial and trans-ovarian transmission occurs

• 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
  • Causes haemolysis and haemoglobin pigmentation
  • Causes haemolytic anaemia, haemoglobinuria and fever

• 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
    • Vector is Haemaphysalis

• 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
    • Vector is Boophilus

• 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

• Few infected 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

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

• Merozoites appear in macrophages one to three days before they are observed in erythrocytes

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
  • Causes East Coast Fever
    • Severe, proliferative lymphatic disease of cattle
    • Central and Eastern Africa
    • Transmitted by Rhipicephalus appendiculatus
    • Trans-stadial transmission

• 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

• Clinical signs
  • Pyrexia
  • Enlarged local lymph node
    • Usually parotid lymph node as Rhipicephalus appendiculatus feeds in the ear
  • Loss of condition

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

• Post-mortem
  • Pulmonary oedema
  • Gut mucosal haemorrhages
  • Lymph node and splenic cellular atrophy

Control

• Integrated control of both the tick vector and disease
  • Vaccination and Ectoparasiticides

• 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