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Babesia
- 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
- 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
- B. canis canis is the most important
- 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
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
- 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
- Causes East Coast Fever
- 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
- 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