The Pallas’ cat (Otocolobus manul) is unique among the world’s 36 felid species in exhibiting an extreme susceptibility to toxoplasmosis.1-5 Female Pallas’ cats with chronic immunoglobulin titers to Toxoplasma frequently experience recurrent vertical transmission to developing fetuses or neonates with pronounced mortality.1,5 The objective of this study was to assess the efficacy and safety of a combination drug regimen (i.e., diclazuril and clindamycin) for preventing Toxoplasma transmission during pregnancy in seropositive Pallas’ cats. Two female Pallas’ cats with persistent Toxoplasma serotiters were paired with males during several breeding seasons, resulting in five term pregnancies and the birth of 19 kittens. Drug treatment during pregnancy consisted of either 1) diclazuril (Vecoxan®, Janssen Animal Health, High Wycombe, Buckinghamshire HP144HJ UK; 1 mg/kg p.o.) once per wk (pregnancy #1; 3 kittens), 2) diclazuril (1 mg/kg p.o) twice per wk (pregnancy #2; 5 kittens) or 3) diclazuril (1 mg/kg p.o) once per wk followed by clindamycin (Clintabs®, Virbac Animal Health, Inc., Fort Worth, TX 76137 USA; 16 mg/kg p.o. b.i.d.) for the last 3 wk of pregnancy (pregnancies #3–5; 5, 3 and 3 kittens, respectively). Kittens were removed 1–3 days after birth for hand-raising or fostering to a domestic queen, and treated either with diclazuril (1 mg/kg p.o) once or twice per wk for 12 wk (pregnancy #2) or injectible clindamycin (Hospira Inc., Lake Forest, IL 60045 USA; 10 mg/kg i.m. b.i.d.) for five days followed by a single dose of diclazuril (1 mg/kg p.o.) 2 days later (pregnancies #3–5). Kittens subsequently showing clinical signs suggestive of toxoplasmosis were treated with several antibiotics including ceftriaxone sodium (Rocephin®, Roche Pharmaceuticals, Nutley, NJ 07110 USA), trimethoprim-sulfamethoxazole (Bactrim®, Roche), atovaquone (Mepron®, GlaxoSmithKline, Research Triangle Park, NC 27709 USA) and/or clindamycin at varying dosages. Blood samples collected from Pallas’ cat dams on the day after parturition and kittens older than 12 wk of age were assessed by ELISA for Toxoplasma serotiters (IgM and IgG), and milk and whole blood from Pallas’ cat dams were tested via PCR for Toxoplasma DNA. All deceased kittens were evaluated for gross and histologic evidence of toxoplasmosis.
For the two pregnancies treated with diclazuril alone, only one of eight kittens (12.5%) survived to adulthood and toxoplasmosis was diagnosed histologically in at least one deceased kitten in each litter, suggesting Toxoplasma transmission from the dam. The one surviving kitten developed Toxoplasma titers indicative of exposure. For the three pregnancies treated with a combination of diclazuril and clindamycin, six of eleven (55%) kittens survived to adulthood and no evidence of toxoplasmosis was observed in any deceased kitten. The day after parturition, these Pallas’ cat dams had moderate Toxoplasma IgG titers, but milk and blood samples tested negative for Toxoplasma DNA. All six surviving kittens were seronegative for Toxoplasma exposure after 12 wk of age.
Our results suggest that diclazuril alone is ineffective in preventing Toxoplasma transmission in utero, but that a combination regimen of diclazuril and clindamycin used sequentially in pregnant females and their neonatal kittens may have some efficacy. However, it is unknown if this drug regimen had any effect on neonatal mortality unrelated to toxoplasmosis and further studies addressing drug safety may be warranted.
The assistance of the veterinary and animal care staff at the Cincinnati Zoo and Botanical Garden is gratefully acknowledged.
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