Babesiosis in Animals

• What it is:

  • A clinical disease.

  • Caused by infection with protozoa of the genus Babesia.

  • A blood parasite.

  • Affects domestic animals (cattle, horses, sheep, goats, pigs, dogs, and cats), wildlife, and occasionally humans.

  • Can be a zoonotic disease affecting humans.

  • Typically characterized by fever and intravascular hemolysis.

  • Intravascular hemolysis leads to progressive anemia, hemoglobinuria, and jaundice.

  • May result in death (the disease may be fatal).

• Etiology (Cause):

  • Protozoan parasites of the genus Babesia.

  • Intraerythrocytic parasites (found inside red blood cells).

  • Phylum Apicomplexa, Order Piroplasmida.

  • More than 100 species exist.

  • Traditionally classified by morphology, vector, and host specificity, but molecular characterization suggests greater complexity.

  • Examples of species in different hosts:

    • Cattle: B. bovis (virulent), B. bigemina (less virulent strains), B. divergens, B. major.

    • Horses: Theileria (formerly Babesia) equi (small, more pathogenic), B. caballi.

    • Sheep/Goats: B. ovis, B. motasi.

    • Pigs: B. trautmanni (severe disease), B. perroncitoi.

    • Dogs: B. canis, B. vogeli, B. rossi (varying severity), B. gibsoni (smaller, chronic disease, severe anemia, not readily treated).

    • Cats: B. felis (illness of varying severity, mostly southern Africa, unusual lack of response to normal babesiacides), B. leo, B. lengau, less-well defined species.

    • Humans: B. microti (North America), B. divergens (Europe), B. duncani, B. venatorum, less well-defined species.

• Hosts:

  • Domestic animals.

  • Wildlife.

  • Humans (occasionally).

  • Specific hosts listed above under Etiology.

• Transmission & Epidemiology:

  • Transmitted by ixodid ticks.

  • Geographic distribution is determined by the distribution of tick vectors.

  • Main vectors for B. bigemina and B. bovis are 1-host Rhipicephalus (Boophilus) spp ticks (widespread in tropical/subtropical areas).

  • Other vectors mentioned: Ixodes ricinus (B. divergens), Haemaphysalis punctata (B. major), Rhipicephalus, Dermacentor, Hyalomma (equine), Rhipicephalus bursa (B. ovis), Haemaphysalis spp (B. motasi), Rhipicephalus spp (B. trautmanni), Dermacentor reticularis (B. canis), Rhipicephalus sanguineus (B. vogeli), Haemaphysalis elliptica (B. rossi).

  • Transmission occurs transovarially in Rhipicephalus spp ticks. Blood stages ingested by tick, undergo multiplication, infect eggs.

  • Transmission to host when larvae (B. bovis) or nymphs and adults (B. bigemina) feed.

  • Experimental transmission by blood inoculation is possible.

  • Mechanical transmission by insects or surgery has no practical importance.

  • Intrauterine infection reported, but is rare (more common with T. equi).

  • Oral and direct "cat-to-cat" transmission does not occur [implied by contrast with experimental methods in previous source about Cytauxzoonosis].

  • In endemic areas for cattle, factors determining risk include calf immunity (~6-8 months), acquired immunity after recovery, and breed susceptibility (Bos indicus more resistant).

  • Outbreaks can occur with reduced tick numbers (leading to naive adults), introduction of susceptible cattle, or incursion of infected ticks.

  • Historical epizootics linked to movement of infected cattle and ticks.

  • Zoonotic transmission to humans via infected tick bites or contaminated blood transfusion.

• Pathogenesis:

  • Intraerythrocytic parasites.

  • Pathogenic effects primarily relate to erythrocyte destruction.

  • Virulent strains (B. bovis) cause hypotensive shock syndrome, generalized inflammation, coagulation disturbances, and erythrocytic stasis in capillaries.

  • CNS involvement can occur with B. bovis due to adhesion of parasitized erythrocytes in brain capillaries.

• Clinical Findings:

  • Acute babesiosis typically runs a course of ~1 week or less.

  • First signs: lethargy, weakness, depression, and fever (frequently ≥106°F [41°C]).

  • Later signs: inappetence, anemia, jaundice, weight loss.

  • Final stages: hemoglobinemia and hemoglobinuria.

  • Less often: CNS signs (B. bovis), abortion (late-term cows), temporary infertility (bulls).

  • Many animals recover, but some may die if not treated.

  • Recovered animals remain infected for years (B. bovis) or months (B. bigemina) in a carrier state with no clinical signs.

• Postmortem Lesions (particularly with B. bovis):

  • Enlarged and friable spleen.

  • Swollen liver with enlarged gallbladder containing thick granular bile.

  • Congested, dark-colored kidneys.

  • Generalized anemia and jaundice.

  • Often hemoglobinuria (B. bigemina).

  • Congestion or petechiae in other organs (brain, heart).

• Diagnosis:

  • Based on clinical findings and history (presumptive, requires confirmation).

  • Light microscopic evaluation of blood smears is essential to confirm.

    • Rapid and inexpensive, but requires expertise.

    • Smears from capillaries (ear, tail tip) improve B. bovis detection.

    • Postmortem smears from kidney, spleen, extremity blood vessel.

    • Poor sensitivity for detecting carrier state.

    • Species identification by morphology possible with expertise. B. bovis is small (~1–1.5 mcm), paired at an obtuse angle; B. bigemina is larger (3–3.5 mcm), paired almost parallel or acute angle. Single forms common.

  • PCR assay: More sensitive than light microscopy, useful for carrier state or chronic infection, and to differentiate/characterize isolates. Note: detection doesn't always mean it's the cause of current disease.

  • Serologic testing: Detect antibodies in carrier animals (indirect fluorescent antibody test, ELISA); not useful in acute stage.

  • Subinoculation: Blood into a susceptible animal (like a splenectomized calf) to confirm carrier state (occasionally justified).

• Treatment, Control, and Prevention:

  • Babesiacides:

    • Most common treatments are imidocarb dipropionate and diminazene aceturate. (Availability and use may be restricted; follow manufacturer recommendations).

    • Dosages for cattle mentioned.

    • Note: B. felis (cats) and B. gibsoni (dogs) may lack response to normal babesiacides.

  • Supportive Treatment: Advisable, especially in valuable animals.

    • May include anti-inflammatory drugs, corticosteroids, and fluid therapy.

    • Blood transfusions may be lifesaving in very anemic animals.

  • Tick Control: Via acaricides or management practices.

    • Can reduce tick burdens and transmission rates.

    • Chemical control cannot be relied upon to prevent transmission.

    • Acaricide resistance is an increasing problem.

    • Useful before moving animals from tick-infested areas to prevent introduction to tick-free areas.

    • Eradication rarely feasible on premises, possible regionally.

  • Use of Resistant Breeds: Bos indicus-based breeds commonly used in cattle.

  • Vaccination: Using live attenuated strains available in some countries (Argentina, Australia, Brazil, Israel, South Africa, Uruguay).

    • Available in chilled or frozen form.

    • One vaccination produces adequate immunity for the typical productive lifespan.

    • Commercial vaccines based on recombinant antigens are not yet available.

• Key Points (Summary):

  • Widespread in domestic and wildlife populations, occasionally infects humans.

  • Ixodid ticks are the vectors.

  • Serious and economically important cause of illness and death in cattle in tropical and subtropical areas.

  • Control based on specific drug treatments, tick control strategies, and vaccination in some countries.