Cytauxzoonosis in Dogs and Cats: A Comprehensive Guide

Cytauxzoonosis in Dogs and Cats: A Comprehensive Guide

Introduction

Cytauxzoonosis is a severe, often fatal tick-borne disease affecting domestic cats, caused by Cytauxzoon felis, a protozoan parasite. While cytauxzoonosis is primarily a feline disease, recent studies have indicated potential infections in dogs. The disease is prevalent in the southeastern and south-central United States but has been reported in other regions as well. Due to its rapid progression and high mortality rate, cytauxzoonosis is a critical concern for veterinarians and pet owners.

What is Cytauxzoonosis?

Cytauxzoonosis is a tick-borne hemoprotozoal disease caused by Cytauxzoon felis in cats. The disease is often rapidly fatal in domestic cats, whereas bobcats (Lynx rufus) serve as natural reservoirs and typically experience subclinical infections.

Although cytauxzoonosis has primarily been documented in felines, emerging research suggests that dogs can also be susceptible to a similar infection caused by Cytauxzoon spp. However, cases in canines remain rare, and the pathogenicity in dogs is not well understood.

Transmission of Cytauxzoonosis

Cytauxzoonosis is transmitted through the bite of infected ticks. The primary vectors of Cytauxzoon felis are the Amblyomma americanum (lone star tick) and Dermacentor variabilis (American dog tick). These ticks acquire the parasite from infected bobcats or other wild felids and transmit it to domestic cats during a blood meal.

Lifecycle of Cytauxzoon felis

  1. Tick Ingestion of Infected Blood: A tick feeds on an infected bobcat or wild felid and ingests Cytauxzoon felis organisms.
  2. Parasite Development in the Tick: The parasite undergoes replication within the tick’s salivary glands.
  3. Transmission to Domestic Cats: When the infected tick bites a domestic cat, Cytauxzoon felis enters the bloodstream.
  4. Schizogony in Macrophages: The parasite multiplies in macrophages, leading to widespread endothelial blockage and severe systemic illness.
  5. Erythrocytic Stage: The parasite also invades red blood cells, leading to hemolysis, anemia, and death if untreated.

While direct transmission between cats is not known to occur, studies suggest that blood transfusions from infected cats could be a potential risk.

Clinical Signs of Cytauxzoonosis in Cats

Cytauxzoonosis in cats progresses rapidly, with symptoms appearing 5 to 14 days after infection. The disease can be divided into three phases:

  1. Prepatent Phase (Asymptomatic Period)

    • Occurs within the first few days of infection
    • The parasite undergoes schizogony within macrophages

  2. Acute Phase (Symptomatic Period)

    • Sudden onset of lethargy and anorexia
    • High fever (104–106°F)
    • Pale or icteric mucous membranes (jaundice)
    • Tachypnea and dyspnea (labored breathing)
    • Lymphadenopathy (enlarged lymph nodes)
    • Splenomegaly and hepatomegaly (enlarged spleen and liver)
    • Severe dehydration and weakness

  3. Terminal Phase

    • Hypothermia and profound lethargy
    • Multi-organ failure
    • Disseminated intravascular coagulation (DIC)
    • Death within 1–2 days of severe clinical signs

Without treatment, mortality rates exceed 90%, making early diagnosis and intervention crucial.

Cytauxzoonosis in Dogs: Emerging Evidence

While cytauxzoonosis is well-documented in felines, recent studies have identified Cytauxzoon spp. in dogs, particularly in regions where feline cytauxzoonosis is endemic. However, unlike in cats, the disease in dogs appears to be subclinical or mild, with limited reports of severe cases.

Possible Clinical Signs in Dogs

  • Mild fever
  • Lethargy
  • Anemia
  • Enlarged spleen
  • Occasional thrombocytopenia

Because canine cytauxzoonosis is still being researched, its true impact on dogs remains uncertain. More studies are needed to determine whether Cytauxzoon spp. pose a significant threat to canines.

Diagnosis of Cytauxzoonosis

Early diagnosis is critical to improving survival rates in infected cats. Diagnosis is based on clinical signs, blood tests, and advanced laboratory techniques.

Diagnostic Tests for Cytauxzoonosis

  1. Blood Smear Examination

    • Giemsa-stained blood smears reveal piroplasms (ring-shaped organisms) within red blood cells.
    • Schizonts may be visible in macrophages from blood, spleen, or liver aspirates.

  2. Polymerase Chain Reaction (PCR) Test

    • Detects Cytauxzoon felis DNA in blood samples.
    • Highly sensitive and specific.

  3. Complete Blood Count (CBC) and Biochemistry Panel

    • Severe anemia and thrombocytopenia.
    • Hyperbilirubinemia and elevated liver enzymes due to liver damage.

  4. Histopathology

    • Examination of tissues post-mortem reveals widespread macrophage infiltration with schizonts.

Treatment of Cytauxzoonosis

Cytauxzoonosis is a medical emergency that requires aggressive treatment. While historically considered untreatable, new therapeutic protocols have improved survival rates.

Standard Treatment Approach

  1. Combination Antiprotozoal Therapy

    • Atovaquone (15 mg/kg PO q8h) + Azithromycin (10 mg/kg PO q24h) for 10 days
    • This combination has increased survival rates to 60% or higher.

  2. Supportive Care

    • Intravenous fluid therapy to manage dehydration and electrolyte imbalances.
    • Oxygen therapy for respiratory distress.
    • Blood transfusions in severe anemia cases.

  3. Pain Management and Nutritional Support

    • Pain relief with opioids (buprenorphine, fentanyl).
    • Assisted feeding or enteral nutrition if needed.

Despite treatment, prognosis remains guarded, and early intervention significantly improves outcomes.

Prevention of Cytauxzoonosis

Because cytauxzoonosis has a high fatality rate, prevention is the best strategy.

Effective Preventive Measures

  1. Tick Control

    • Use veterinarian-approved tick preventatives (fluralaner, selamectin, fipronil).
    • Inspect pets for ticks daily and remove them promptly.

  2. Restrict Outdoor Access

    • Keep cats indoors to minimize tick exposure.
    • Avoid wooded areas where ticks are prevalent.

  3. Environmental Management

    • Treat yards with acaricides to reduce tick populations.
    • Maintain short grass and remove leaf litter to discourage tick habitats.

  4. Regular Veterinary Check-ups

    • Routine screenings for at-risk cats in endemic areas.

Conclusion

Cytauxzoonosis is a deadly tick-borne disease in cats, with emerging evidence of canine infections. Due to its high mortality rate, early diagnosis, aggressive treatment, and effective tick prevention are crucial for managing this disease. Pet owners should be vigilant in tick control measures, while veterinarians must stay updated on evolving diagnostic and treatment strategies.

By raising awareness and implementing preventive measures, we can reduce the impact of cytauxzoonosis on feline and canine populations.  

References

  1. Birkenheuer, A. J., Le, J. A., Valenzisi, A. M., Tucker, M. D., Levy, M. G., & Breitschwerdt, E. B. (2006). Cytauxzoon felis infections are present in Bobcats (Lynx rufus) in North Carolina. Journal of Clinical Microbiology, 44(4), 1621-1624.

  2. Brown, H. M., Latimer, K. S., Erikson, L. E., Cashwell, M. E., & Britt, J. O. (2008). Detection of Cytauxzoon felis infection in cats by polymerase chain reaction. Journal of Veterinary Diagnostic Investigation, 20(3), 282-285.

  3. Cohn, L. A., Birkenheuer, A. J., Brunker, J. D., Ratcliff, E. R., & Craig, A. W. (2011). Efficacy of atovaquone and azithromycin or imidocarb dipropionate in cats with acute cytauxzoonosis. Journal of Veterinary Internal Medicine, 25(1), 55-60.

  4. Meinkoth, J., Kocan, A. A., Whitworth, L., Murphy, G., Fox, J. C., & Woods, J. P. (2000). Cats surviving natural infection with Cytauxzoon felis: 18 cases (1997–1998). Journal of Veterinary Internal Medicine, 14(5), 521-525.

  5. Reichard, M. V., Meinkoth, J. H., Edwards, A. C., Snider, T. A., Meinkoth, K. R., Heinz, R. E., & Little, S. E. (2009). Transmission of Cytauxzoon felis to a domestic cat by Amblyomma americanum (Acari: Ixodidae). Journal of Medical Entomology, 46(3), 537-540.

  6. Sherrill, M. K., & Cohn, L. A. (2015). Cytauxzoonosis: Diagnosis and treatment of an emerging disease. Journal of Feline Medicine and Surgery, 17(11), 940-948.

  7. Shock, B. C., Birkenheuer, A. J., Patel, R., Olfenbuttel, C., Beringer, J., Grove, D. M., Peek, M., & Beall, M. J. (2012). Occurrence of Cytauxzoon felis infections in bobcats and piroplasmic infections in cougars from 18 states across the USA. Veterinary Parasitology, 190(3-4), 469-473.

  8. Woods, J. P., & Reichard, M. V. (2019). Cytauxzoon felis infections in domestic cats: The role of reservoir hosts and implications for disease management. Veterinary Parasitology: Regional Studies and Reports, 18, 1000349


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