Successful Treatment of Cryptosporidiosis in 2 Common Marmosets (Callithrix jacchus) by Using Paromomycin

Abstract

Two pair-housed, 1-y-old common marmosets (Callithrix jacchus) had intermittent loose feces and weight loss for approximately 2 mo. Cryptosporidum parvum was identified by ELISA in the feces of both animals. CBC and blood chemistry values, including liver enzymes, were within normal range. Both marmosets were treated with the antibiotic paromomycin (15 mg/kg PO) twice daily for 28 d. Resolution of clinical signs coincided with treatment. Three follow-up samples, taken 2 wk apart after treatment was finished, were negative for cryptosporidium ELISA in both animals. Paromomycin should be considered for treatment of cryptosporidiosis in marmosets.

Cryptosporidium was first described in laboratory mice by Tyzzer in 1907.²⁰ However, the organism was not considered to be pathogenic until the 1970s, when it was identified as causing disease in mammals, primarily calves.^15,18 Cryptosporidiosis continues to be a serious disease in dairy cattle, causing high morbidity and mortality in neonatal calves.²⁶ Cyptosporidiosis has been identified as a zoonotic disease, particularly among veterinary students caring for sick calves.^7,11,17 Cryptosporidiosis caused by Cryptosporidium parvum is now considered a serious pathogen in immunocompromised subjects and one of the most serious opportunistic infections complicating disease in AIDS patients.²² Several recent book chapters and review articles discuss the epidemiology, treatment, biology, and pathogenesis of human and veterinary cryptosporidiosis.⁵,^13,22,23

Cryptosporidiosis is considered to be a self-limiting disease in immunocompetent human patients,²¹ nursery-reared infant macaques (Macaca mulatta),¹⁴ and other animals.¹⁰ The disease has an acute onset in people (3 to 7 d), and diarrhea and abdominal cramping generally lasts 7 to 10 d. Cryptosporidiosis may be asymptomatic in marmosets (Callithrix jacchus)¹⁰ but has been reported to cause enterocolitis in immunocompetent marmosets, for which supportive therapy is the only published treatment.¹²

Paromomycin is an aminoglycocide antibiotic that has been one of the most widely used agents to treat cryptosporidiosis in immunosuppressed human patients.^3,4,13,19 The drug has shown efficacy in experimentally infected animal models,^1,8,24 for prophylaxis in outbreaks of ruminants,⁶ and in cats with clinical cryptosporidiosis,² although paromomycin toxicity in cats has been reported.⁹

Here we describe the use of paromomycin to treat cryptosporidiosis in 2 marmosets, with subsequent resolution of clinical signs.

Case Report

Two pair-housed marmosets arrived from a quarantine facility in good condition. Marmoset no. 1 was 17 mo and marmoset no. 2 was 12 mo of age at the time of arrival. One week after arrival, both marmosets were reported to have loose feces mixed with fresh blood and mucus. On physical examination, both marmosets were found to be thin but lacking any remarkable changes. Marmoset no. 1 had lost 34 g (8% of body weight) and the other had lost 64 g (25% of body weight) since they were weighed 2 wk previously at the quarantine facility. Blood was drawn and submitted to a commercial laboratory (IDEXX Laboratories, Fremont, CA) for CBC and blood chemistry analysis. Fecal samples were submitted for culture (Campylobacter, Salmonella, Shigella, and Yersinia), fecal flotation for ova and parasites, and ELISA for Crypotosporidium and Giardia. The marmosets were weighed daily and placed on a supplemental feeding schedule, which included hand-feeding nutritious, palatable foods. Weight loss diminished but the loose stool persisted during the wait to receive culture results (Figure 1).

Figure 1.

Marmoset weights during the course of treatment with paromomycin.

All the clinical data were normal except that the fecal samples were ELISA-positive for C. parvum. Furthermore, feces collected from 10 other marmosets housed in the same room were negative for C. parvum.

Review of the records from the quarantine facility revealed that the marmosets had arrived 6 wk previously from an outdoor facility in Florida. The marmosets had been noted as having diarrhea and low body weight on arrival into quarantine. Campylobacter coli had been cultured from the feces of the marmosets. Although treatment with tetracycline followed by cephalexin resulted in resolution of clinical signs, fecal cultures continued to yield Campylobacter coli. The marmosets were not tested for Cryptosporidium at that time.

At our facility, treatment with paromomycin began 2 wk after the first episode of loose, bloody feces was observed. Treatment dose and agent were based on the human literature and consisted of paromomycin (15 mg/kg PO) twice daily, initially for 2 wk. The antibiotic was mixed into a treat-food vehicle, administered by syringe directly into the mouth, and appeared to be tolerated well in that no adverse reactions were observed. Because feces remained loose on day 14 of treatment, we added 2 weeks to the treatment period. No additional loose feces were noted after completion of the full 28-d treatment, and both marmosets gained weight during the treatment period (Figure 1). Fecal samples collected and submitted for cryptosporidium ELISA at the end of the treatment period and 2 additional times, 2 wk apart, all were negative.

Discussion

Two marmosets with cryptosporidiosis were treated with paromomycin, and their treatment coincided with the resolutions of clinical signs and cessation of shed organisms detectable by ELISA. It is plausible that these animals ‘self-cured’ and that the paromomycin treatment was simply coincidental. Indeed the weight-loss in marmoset no. 2 stabilized prior to paromomycin treatment; however, loose feces persisted and were even increasing in frequency (Figure 1). Both marmosets were being handfed twice daily and this may have contributed to the weight gain. In addition, the long period of clinical disease (at least 2 mo; weight records were not available prior to arrival in quarantine) indicates that cryptosporidiosis was chronic in these 2 marmosets. Regardless, treatment did coincide with both resolution of clinical signs and with ceasing of shedding organisms.

Review of veterinary literature reveals few treatment options for animals with clinical cryptosporidiosis. The histopathology of cryptosporidiosis may provide some insight into the difficulty of treating the disease. Cryptosporidia are intracellular extracytoplasmic organisms with life cycles similar to those of many apicomplexan protozoan parasites. However, cryptosporidia are unique in that they alter the enterocyte membrane to create a niche for themselves between the cell membrane and cytoplasm (Figure 2). Cryptosporidia therefore are separated from the gut lumen by this parasitophorus vacuolar membrane (derived from the host cell membrane) and from the rest of the host cell cytoplasm by a structure unique to cryptosporidia, called the feeder organelle membrane. Neither the mechanisms of this process, nor the implications in terms of accessibility to the parasite in this unusual location, are understood. However, the location and nature of this dual sequestration from the lumen of the gut and from the cell cytoplasm may explain why the disease is difficult to target pharmaceutically.^13,22

Figure 2.

Schematic drawing of Cryptosopirium organism in host enterocyte. CO, cryptosporidial organism; FOM, feeder organelle; HM, host membrane; PV, parasitophorous vacuole.

Paromomycin is poorly absorbed from the gastrointestinal tract; the resulting high concentration in the gut may account for its ability to treat cryptosporiosis in some cases.¹³ Human patients with biliary crytosporidiosis are less likely to be treated successfully with paromomycin.²⁵ Elevated serum liver enzymes, indicating biliary involvement, is considered poor prognosis for treatment (other than immune reconstitution in AIDS patients) in human cryptosporidiosis cases.¹⁶ The decision to treat these marmosets with paromomycin was made after reviewing their serum chemistry results, which were within normal range.

Diarrhea in small primates can be life-threatening. Supportive treatment should always be instituted, but paromomycin should be considered as a treatment adjunct to potentially hasten clinical resolution of cryptosporidiosis.