Clindamycin in the Treatment of Babesia gibsoni Infections in Dogs

Introduction

Among Babesia species that infect a wide variety of animals, Babesia canis (B. canis) and Babesia gibsoni (B. gibsoni) are known as causative agents of canine babesiosis.^1–6 Clinical findings of canine babesiosis are weakness, depression, lethargy, anorexia, malaise, anemia, fever, splenomegaly, and hemoglobinuria.^25–11 Babesia canis induces more acute and rapid hemolysis than does B. gibsoni.¹⁰ Babesia gibsoni infection in dogs has long been problematic in Japan, especially in the western region, and in recent years, the geographic range of infection has spread to include the eastern region of Japan as well. Chemotherapeutic agents used for treatment of canine babesiosis are diminazene aceturate,^a phenamidine isethionate,^b and imidocarb.^c Only the first two drugs (i.e., diminazene aceturate and phenamidine isethionate) have demonstrated efficacy against B. gibsoni.^311–13 In Japan, diminazene aceturate has been utilized for treatment of B. gibsoni infection. Although this medicine is effective against B. gibsoni, it sometimes induces side effects such as weakness, irritability, paralysis, profound depression, and fatal central nervous system hemorrhage.^11–13 Treatment of or spontaneous recovery from an acute episode of Babesiosis frequently fails to clear the organism from the host, resulting in a carrier stage,³ with the potential for relapse.^2391314 Clinicians in Japan often have little choice but to repeat therapy using this medicine, despite concern about side effects, which can be induced by repeated administration. Recently, diminazene aceturate production has been halted in Japan; therefore, an alternative chemotherapeutic agent effective against B. gibsoni and having few side effects is urgently needed. Clindamycin has been successfully used for the treatment of Babesia microti (B. microti) infection in hamsters and humans and for the treatment of B. canis infection.^215–17 In the authors’ previous study, it was determined that clindamycin might be useful as an alternative drug for the treatment of Babesia rodhaini (B. rodhaini) infection in mice, and it was found to induce resistance to challenge infection in cured mice.¹⁴

Clindamycin administration has resulted in few side effects in dogs. No clinical problems were observed in dogs that were orally administered a high dose (300 mg/kg body weight) of clindamycin for 6 months.¹⁸ Based on these findings, the authors investigated the potential therapeutic effects of clindamycin on B. gibsoni in experimentally infected dogs.

Materials and Methods

Results

Percentages of parasitized red blood cells of untreated and clindamycin-treated groups on day 7 after inoculation (pretreatment value) were (mean±SD) 1.40%±0.50% and 1.50%±0.91%, respectively. Treated and untreated dogs showed peak parasitemia levels of 3.37%±0.40% and 4.53%±1.50%, respectively, on the 14th day after infection (no significant difference was found between them). Then the levels of parasitemia in treated dogs tended to be lower than those of untreated dogs until 73 days after infection [Figure 1].

The majority (approximately 70%) of B. gibsoni parasites in erythrocytes of untreated dogs demonstrated typical morphology (e.g., small and rounded shape with clear cytoplasm and a clear nucleus in the edge of the cell) in May-Grünwald and Giemsa-stained blood smears in untreated dogs on day 14 [Figure 2A] and on day 19 [Figure 2D]. Conversely, B. gibsoni parasites in clindamycin-treated dogs demonstrated morphological changes that indicated a significant incidence (approximately 85%) of parasite degeneration; these degenerative changes included a torn nucleus [Figures 2B, 2F], a segmented nucleus localized within the limbic region of the organism [Figure 2C], a size-reduced nucleus [Figure 2E], and a swollen organism cytoplasm [Figure 2E] or a decrease [Figures 2B, 2E] or disappearance of the cytoplasm [Figure 2E].

Packed cell volume (PCV) of untreated and treated dogs before infection were 50.7%±4.8% and 49.1%±6.7%, respectively (reference range, 33% to 58%). Their levels began to decrease by day 7. The PCV of untreated dogs decreased markedly, reaching nadir values of 14.4%±1.6% on day 28. In contrast, after reaching nadir values of 25.4%±6.5% on day 14, the PCV of treated dogs increased to 28.4%±10.1% on day 21 and 38.63%±6.9% on day 36. However, the PCV in the treated group began to decrease again, as evidenced by a decline to 36.67%±7.8% on day 42 and a subsequent decline to 26.57%±9.9% on day 49, after which they increased. On day 108, untreated dogs still showed a slight anemia (PCV, 38.7%±3.3%), whereas treated dogs showed almost full recovery (46.3%±4.0%) from anemia. The hemoglobin concentration and the erythrocyte counts paralleled the PCV [Figure 1].

Percentages of reticulocytes began to increase on day 7 after infection. On days 21, 35, 42, and 49, reticulocytosis in untreated dogs was significantly (P<0.01) higher (8.8%±4.2%, 10.4%±1.9%, 10.3%±3.2%, and 6.9%±3.0%, respectively) than the reticulocytosis of treated dogs (2.6%±0.6%, 1.4%±0.1%, 1.3%±0.1%, and 2.2%±0.4%, respectively). Mean corpuscular volume paralleled the degree of reticulocytes.

Clinical findings were evaluated daily. Hemoglobinuria was observed for 12 days (from days 16 to 28) in untreated dogs, but only for 4 days (from days 14 to 18) in treated dogs. In all dogs, pyrexia was observed from day 1 after infection to approximately day 7. Temperatures of clindamycin-treated dogs decreased with the start of medical treatment and returned to normal after day 14, while the temperatures of untreated dogs fluctuated and were significantly higher than temperatures of the treated dogs, especially on days 21 and 24 (data not shown). Other clinical findings included anorexia, listlessness, and pallor of the mucous membranes; these findings were more prevalent in untreated than treated dogs, especially from days 21 to 35. No side effects to clindamycin were observed in treated dogs.

Discussion

The authors’ study demonstrated clindamycin to be an effective treatment for babesiosis without concurrent side effects; to date, no medication has demonstrated this dual benefit.^211–14 Clindamycin is believed to act by binding to the 50S ribosomal subunit of the susceptible microorganisms, thereby inhibiting peptide bond formation.²⁰ In the present study, clindamycin therapy suppressed the development of parasitemia and therefore reduced the clinical symptoms characteristic of Babesia infection, such as anemia, anorexia, and listlessness; however, it did not completely eliminate the parasites from the peripheral blood at the dosage used. The present results agreed well with those of other reports regarding the benefits of clindamycin treatment for B. microti infection in humans and B. canis infection in dogs; principally, that clindamycin used alone or in combination with quinine effected an earlier resolution of infection.^2915–17

While parasitemia levels showed no significant difference between untreated and clindamycin-treated experimentally infected dogs, there were marked differences in organism morphology between these groups. Clindamycin-treated dogs showed morphological changes that indicated degeneration of parasites, such as segmentation, size reduction, localization in the cell limbic and/or torn state of the nucleus, and decrease or disappearance of the cytoplasm; these degenerative changes might be indicative of reduced organism viability and, therefore, the improvement in clinical symptoms following clindamycin treatment.

Clindamycin treatment resolved anemia and other clinical findings following the acute stage of infection, despite a transient relapse and the lack of complete parasite elimination. This finding indicates that a certain level of host exposure to parasitic antigen is necessary for the host to acquire a protective immunity. A drug such as clindamycin, which appears to have a static rather than cidal effect on B. gibsoni, may be able to work synergistically with the host’s protective immune responses.² At the end of this study, clindamycin-treated dogs still demonstrated weak parasitemia, a slight increase in reticulocyte counts, and a slight decrease of platelet counts, although the dogs had recovered from anemia and other clinical symptoms. Dogs that survive an acute crisis of babesiosis develop a state of premunition. Premunition is referred to as the immunity to infection and is a delicate balance between the host’s immune response and the parasite’s ability to induce clinical disease.³ Therefore, the purpose and strategy of babesiosis therapy, rather than to quickly and completely eliminate the parasites from hosts, have been to suppress the proliferation of parasites without any adverse side effects.¹⁴ Based on the results of this study, clindamycin appears to be effective at accomplishing this.

Severe thrombocytopenia appeared in the early stage of babesiosis prior to peak parasitemia, was closely related to the development of parasitemia, and was evident throughout the experiment in all infected dogs. This decline is postulated to be due to splenic sequestration secondary to Babesia-induced splenomegaly, and the occurrence of thrombocytopenia has been suggested as a good parameter for assessing the status of disease due to B. gibsoni infection.⁸²¹

The administration of clindamycin did not induce any adverse side effects in the dogs of this study. In the authors’ previous study, clindamycin was found to be an effective drug for the treatment of babesiosis in mice and to induce resistance to challenge infection in cured mice.¹⁴ The finding in the present study suggests that clindamycin might be useful as a therapeutic medicine for canine B. gibsoni infection, especially for relapse after treatment with diminazene aceturate.

Acknowledgments

The authors thank Dr. Naochika Matsunuma, the director of Medicinal Safety Research Laboratories, Sankyo Co., Ltd., Sizuoka, Japan, for the gift of beagles.