Coccidiosis (Isospora and Sarcocystis species) is an enteric infection, traditionally associated
with Isospora canis (dogs) and Isospora felis (cats) as potential pathogens. Other species of
Isospora may be present. Strictly host speciﬁc, i.e., no cross-transmission.
Coccidia is one of the most commonly seen parasites in cats, and is most common in young
kittens and more likely to be seen where conditions of poor sanitation, stress and crowding
exist. Several references in veterinary literature suggest that almost every cat will become
infected by coccidia at some point in their life. Cats acquire the parasite by ingesting any
source that has been contaminated by infected cat feces or by ingestion of infected rodents or
other meat sources. These organisms reproduce themselves inside the lining cells of the
intestinal tract. As the new organisms emerge from these host cells, the intestinal cell is killed
in the process. The life cycle of Coccidia takes only a few hours to a few days and new
organisms are again passed in the feces. This cycle is the major cause of re-infection which
may appear as a persistent infection.
Infected cats may exhibit weight loss, weakness, dehydration and diarrhea with possibly
blood and/or mucus being present. Kittens, immunocompromised or otherwise weakened cats
will have more severe symptoms. Older and otherwise healthy cats may exhibit no symptoms
Common name: Coccidia
The unsporulated oocyst leaves the cat in the feces. It takes 3 days in the environment to
develop to the infective, sporulated stage (which contains 4 sporozoites in each of 2
sporocysts). The cat can become infected by ingesting a sporulated oocyst or a mouse which
has ingested an infective oocyst. When a rodent ingests the infective oocyst, the sporozoites
invade intestinal cells and encyst as bradyzoites. The bradyzoite is infectious to the cat. When
the cat eats an infective oocyst or a rodent with bradyzoites in its tissues, the zoites invade
the intestinal cells and develop to the schizont stage. The schizonts release more zoites
which invade new cells and give rise to the next generation of schizonts. There are 3
generations of schizonts. Zoites released from the last generation of schizonts invade cells
and form gametocytes. The male gametocyte releases gametes which fuse with the female
gametocytes and form oocysts. The oocysts rupture out of the cells and are voided with the
feces. It is 7 or 8 days between the initial infection of the cat and the release of oocysts.
During its ﬁrst infection a cat will shed oocysts for 10 to 11 days.