An Overview of Feline Babesiosis

V. Bishop, DVM; H. M. Brown, DVM; K. S. Latimer, DVM, PhD, DACVP

Class of 2006 (Bishop) and Department of Pathology (Brown, Latimer), College of Veterinary Medicine, University of Georgia, Athens, GA, 30602-7388

Introduction

Babesiosis is a tickborne hemoprotozoal disease affecting a variety of domestic and wild animals and humans worldwide. Babesiosis in domestic cats has been reported sporadically from various countries including France, Germany, Thailand, India, and Zimbabwe. However, significant clinical disease is seen only in South Africa where feline babesiosis is reported regularly from coastal regions.¹ New Babesia species (B. leo, B. venatorum) have been discovered over the past decade, and the level of genetic divergence within other Babesia spp. suggests that new subspecies might be generated.² The use of molecular diagnostics and gene sequencing has disclosed a high level of genetic diversity and also unexpected hosts for Babesia spp.

Etiology

Several Babesia spp. are known to infect wild felids and domestic cats. Babesia herpailuri and B. pantherae are large intraerythrocytic piroplasms of wild felids in Africa that have been transmitted experimentally to the domestic cat.³ In the United States (U.S.), there has been a single report of feline babesiosis detected in Florida cougars.⁴ Infectivity and pathogenicity of this Babesia sp. for domestic cats currently is unknown. Babesia spp. detected in naturally infected domestic cats include B. felis and B. leo from Africa, B. cati from India, B. canis canis from Spain and Portugal, B. microti-like species from Portugal, and B. canis presentii from Israel.⁴ The most common Babesia species to affect domestic cats, B. felis, is a highly pathogenic, small piroplasm found mainly in the coastal areas of southern Africa and the Sudan.^3,4 B. felis usually occurs in cats less than three years of age and does not appear to have a predilection related to sex or breed.^5,6

Epidemiology

Generally, Babesia spp. are transmitted through the bites of infected ticks. Feline babesiosis is assumed to be tickborne, but the definitive vector has not been identified.¹ Once in the host, Babesia spp. infect erythrocytes and replicate to create merozoites. Ticks are infected by ingesting merozoites during feeding, and replication of the parasite within the tick’s salivary cells results in sporozoite formation. When infected ticks feed, the sporozoites are passed into circulation of the host.³ Although a significant host immune response is generated against most Babesia spp. infections, the immune system does not appear to completely eliminate the infection. Thus, animals that recover from babesiosis usually are chronic carriers of the parasite.³ The pathogenicity of Babesia organisms is determined primarily by the species and the strain involved.³

Clinical signs

Feline babesiosis often presents as a chronic, low-grade disease.¹ The most common clinical signs of symptomatic feline babesiosis are anorexia, lethargy, weakness, and a rough haircoat.^6,7 Unlike dogs with babesiosis, fever and icterus are uncommon in cats. In most instances when fever is present, concurrent illness is diagnosed.⁷ Complications of babesiosis include renal failure, pulmonary edema, hepatopathy, and central nervous system signs.^3,6 Many clinical signs are secondary to hemolytic anemia that results from intraerythrocyticinfection by the piroplasms.³ Cats, however, usually adapt to the anemia and may have only mild clinical signs until they are stressed.³ Concurrent infection with Mycoplasma hemofelis (previously known as Hemobartonella felis), feline leukemia virus (FeLV), or feline immunodeficiency virus (FIV) may contribute to the clinical presentation and severity of disease.

Clinicopathologic findings

In cats, the most consistent hematologic finding is a macrocytic, hypochromic, regenerative anemia with inconsistent presence of intraerythrocytic piroplasms.^3,5 The anemia is hemolytic, presumably from both intravascular and intravascular erythrolysis.⁵ In experimental infection, anemia was most profound approximately 3 weeks after infection.⁸ Blood smears reveal increased polychromatophils, Howell-Jolly bodies, nucleated erythrocytes, and anisocytosis indicative of regenerative anemia (Figures 1 and 2).⁷ Erythropagocytosis by monocytes may also be observed.⁷ Secondary IMHA is seen occasionally with a positive agglutination test.^3,5 Cats lack characteristic changes in the leukogram. Thrombocytopenia is common in other species with babesiosis but is an inconsistent finding in cats.^5,8

Serum ALT activity is significantly elevated in the majority of cases whereas ALP and GGT activities generally are within reference intervals.^1,3,5 Increased total bilirubin concentration is commonly detected^3,5 and is most likely a result of hemolysis, but secondary hepatocellular injury may be a contributing factor.¹ Polyclonal gammopathy has been observed in cats with hypergammaglobulinemia.^3,5 Feline babesiosis does not usually alter urea, creatinine, total protein, or cholesterol concentrations or change blood pH.⁹

Figure 1. Regenerative anemia in a feline blood smear. Note the increased polychromasia, anisocytosis, and single metarubricyte (arrow). Modified Wrights stain.	Figure 2. Regenerative anemia in a feline blood smear. Note the increased polychromasia and Howell-Jolly bodies (arrows). Modified Wrights stain.

Diagnosis

A tentative diagnosis of feline babesiosis may be made by identifying intracellular piroplasms within erythrocytes on a Romanowsky or Giemsa-stained peripheral blood smear. However, piroplasms of B. felis and other small piroplasms, including B. leo and Cytauxzoon felis, may be morphologically indistinguishable (Figure 3).⁴ Observing the organisms on a blood smear may also be difficult since the level of parasitemia may be low. Subsequently, the best strategy for definitive diagnosis of intraerythrocytic piroplasms is by molecular methods.²

Polymerase chain reaction (PCR) detection of Babesia spp. DNA is a useful technique to document infection and the test may be performed on a blood sample. Once the presence of piroplasms is ascertained, the individual species of organisms may be identified by comparing genetic sequences of the 18S ribosomal subunit of the parasite’s RNA.^2,4 Sequencing of the first and second internal transcribed spacer (ITS) regions and sequencing of the intervening 5.8S coding region of the rRNA gene is also used for subspeciation.¹⁰

Serologic testing has mainly been used to diagnose canine babesiosis.³ This technique cannot be used reliably in domestic cats because reference intervals for babesiosis-related serologic titers have not been established.

Figure 3. Intracellular piroplasms within erythrocytes in a feline blood smear. Wright-Giemsa stain.

Prognosis

In a published review of 20 cats with experimental babesiosis and 70 cats with naturally acquired babesiosis, all untreated animals eventually died.⁷ Response to appropriate treatment is generally good, but recurrence of clinical disease and chronic infection are possible.⁹ Concurrent infection with Mycoplasma hemofelis, FeLV, and FIV has been identified in a number of cats with feline babesiosis and may have profound effects on response to treatment and outcome of disease.⁵

Treatment

Evaluation of most drugs used to treat experimental infections of Babesia felis in domestic cats have provided variable and questionable results.^11,12 Primaquine phosphate, administered orally or as an intramuscular injection at 0.5mg/kg has been effective but frequently caused vomiting when administered orally and was lethal at dosages exceeding 1mg/kg.¹¹ Primaquine is capable of clearing the parasitemia but does not eliminate B. felis infections.¹² Buparavaquone, enrofloxacine, and danofloxacin have no significant anti-babesial effect.¹² Rifampicin and a sulfadiazine-trimethoprim combination appear to have an anti-parasitic effect but are inferior to primaquine administration.¹² Finally, repeated or chronic antiprotozoal therapy may be necessary to effectively treat feline babesiosis.¹

References

1. Penzhorn BL, Schoeman T, and Jacobson, LS. Feline babesiosis in South Africa: A review. Ann N Y Acad Sci. 2004;1026:183-186.

2. Criado-Fornelio A, Gonzalez-del-Rio MA, Buling-Sarana A, et al. The ‘expanding universe’ of piroplasms. Vet Parasitol. 2004;119:337-345.

3. Taboada J and Lobetti R. Babesiosis. In Greene CE (ed): Infectious diseases of the dog and cat, 3rd ed. Saunders Elsevier, St. Louis, 2006, pp. 722-733.

4. Yabsley MJ, Murphy SM, and Cunningham, MW. Molecular detection and characterization of Cytauxzoon felis and a Babesia species in cougars from Florida. J Wildl Dis. 2006;42:366-374.

5. Schoeman T, Lobetti RG, Jacobson LS, et al. Feline babesiosis: signalment, clinical pathology and co-infections. J S Afr Vet Assoc. 2001;72:4-11.

6. Jacobson LS, Schoeman T, and Lobetti RG. A survey of feline babesiosis in South Africa. J S Afr Vet Assoc. 2000;71:222.228.

7. Futter, GJ and Belonje PC. Studies on feline babesiosis 2. Clinical observations. J S Afr Vet Assoc. 1980;51:143-146.

8. Futter, GJ, Belonje PC, and Van Den Berg A. Studies on feline babesiosis 3. Haematological findings. J S Afr Vet Assoc. 1980;51: 271-280.

9. Futter, GJ, Belonje PC, Van Den Berg A., et al. Studies on feline babesiosis 4. Chemical pathology; macroscopic and microscopic post mortem findings. J S Afr Vet Assoc. 1981;52:5-14.

10. Baneth G, Kenny MJ, Tasker S, et al. Infection with a proposed new subspecies of Babesia canis, Babesia canis subsp. presentii, in domestic cats. J Clin Microbiol. 2004;24:99-105.

11. Potgieter FT. Chemotherapy of Babesia felis infection: Efficacy of certain drugs. J S Afr Vet Assoc. 1981;52:289-293.

12. Penzhorn, BL, Lewis BD, Lopez-Robollar LM, et al. Screening of five drugs for efficacy against Babesia felis in experimentally infected cats. J S Afr Vet Assoc. 2000;71:53-57.

Acknowledgement

The image of the Florida Panther, "Locked and Loaded" by Richard Sloan is featured on his website. Mr. Sloan is a member of Artists for Conservation . The image is copyrighted and used with permission of the artist.

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