December 2018

Diarrhea in a newly adopted kitten

Approximately 4-month-old domestic short-haired, intact female cat showed up to a small animal clinic with a 2-day history of soft stools/diarrhea and occasionally bloody diarrhea. This kitty was adopted from a local animal shelter a week ago, and besides diarrhea, she has been active and seemed happy. A centrifugal fecal flotation with 33% zinc sulfate solution was performed.

Numerous round to slightly oval-shaped objects with a thin, smooth, clear wall were observed. Original magnification, x100 (with x10 objective lens).

Size difference was also observed. Some were bigger - approximately 40-45 x 30 um, and some were smaller - approximately 20-25 x 20 um. Also some contained only a single, round cell inside, but some contained 2 round cells instead. Original magnification, x400 (with x40 objective lens).

A few of them even showed more details inside. Original magnification, x600.

What's your diagnosis?

Answer

Cystoisospora spp. oocysts - the bigger one was C. felis and the smaller one was C. rivolta. 
This protozoan parasite is commonly called as "coccidia" of dogs and cats although other parasites, such as Eimeria, Sarcocystis, Toxoplasma, and Neospora, also fall into this taxonomic group. When oocysts are freshly passed in feces, they typically contain a single, round cell (called "sporoblast"). Developing process (called "sporulation") occurs in the environment - oocyst with a single sporoblast (C. rivolta in photo #2) > sporoblast multiplies into 2 sporocysts (C. felis in photo #2) > each sporocyst contains 4 sporozoites with a single large, round residual body (photo #3). 
Cystoisospora infection is commonly found in young cats, and most of the time cats are asymptomatic. However, when kittens are stressed out due to weaning, change of owner, new environment, etc., clinical coccidiosis can occur and cause diarrhea, abdominal pain, and in a severe case, bloody diarrhea and anemia.  

Reference: 
Anne M. Zajac & Gary A. Conboy. 2012. Veterinary Clinical Parasitology 8th ed.