Causes of Coccidia
In all species except fish, the disease caused by coccidia, known as coccidiosis, is caused by one of three general categories of organisms: Eimeria, Isospora and Cryptosporidium. Dogs are predominantly infected with Isospora canis, while cats tend to become infected with Isospora felis. Eimeria species are not known to parasitize dogs or cats. Cryptosporidium organisms are still being evaluated as the cause of rapid-onset, potentially fatal coccidiosis in very young puppies and kittens. Cryptosporidium are known to be significant pathogens in people. Research studies confirm that dogs can transmit certain types of Cryptosporidium organisms to humans, such as those that normally infect cattle. Some of these parasites are species-specific, so that they are only found in dogs, cats or other host animals.
Young puppies that are malnourished, immunosuppressed or suffering from other concurrent diseases are much more likely to become sick from coccidiosis than are healthy puppies or more mature animals. Newborn puppies born into filthy, cold, damp, crowded or otherwise unsanitary conditions have the greatest risk of suffering from infection with coccidia. Young dogs typically become infected by ingesting the oocyte or cyst form of the parasite, which they pick up either from contaminated premises or from their carrier mother, who may or may not show any signs of disease. Stress, including stress associated with weaning, shipping, dietary changes, extreme weather changes, illness, infection with roundworms or other parasites and other traumatic circumstances, often triggers outbreaks of coccidial diarrhea.
The oocyte (cyst) form of coccidial parasites is eliminated in the feces of infected animals. Once they are free in the environment, the cysts sporulate and become infective to animals that pick them up. Especially in areas with poor environmental hygiene, puppies can even reinfect themselves by ingesting oocytes from their own feces. This is called “auto-infection.” Within about 5 to 7 days after taking in coccidia oocytes, the dog will start to excrete infective cysts in its own feces, creating even more potential sources of infection for other animals.
There are a number of complex changes that occur in coccidial organisms from the time that an oocyst is excreted in feces of an infected dog and the time that the organism matures and reproduces in another animal. The process is complicated but can be quite interesting; if the subject doesn’t interest you, please feel free to skip to the next paragraph or section. In a nutshell, after a coccidia oocyst is passed in the feces of an infected animal, it sporulates under the right temperature, weather and environmental conditions. This is what makes it infective to other animals. Several sporozoites (the infective form of the parasite) develop within secondary cysts inside of the oocyst. When another animal eats the sporulated oocyst, the sporozoites emerge and invade the lining of that animal’s intestines or other tissues. There, they transition into forms of the parasite called schitzonts, and then into merozoites, which undergo a number of asexual replications. The merozoites eventually become either macrogametocytes (females) or microgametocytes (males). When a macrogametocyte becomes fertilized by a microgametocyte, it develops into an oocyst. That oocyst will eventually be excreted in the infected dog’s feces. And the cycle will continue.
The best way to prevent coccidial infection is to prevent the intake of sporulated oocysts by young animals. A high-quality diet and attention to good hygiene will go a long way towards accomplishing this goal. Newborn puppies should receive colostrum from their mothers to strengthen their immune status. Young dogs (in fact, all dogs) should be housed in warm, dry, clean, well-ventilated areas with good bedding and free access to fresh water. Stress should be kept to a minimum in all ways possible.
Dogs that recover from coccidiosis usually remain carriers of the parasites. In other words, while they may no longer be sick, they retain the organisms in their gastrointestinal tract and can still shed infective coccidial cysts in their feces. Known carriers of coccidia should be isolated from other animals and treated with appropriate medications. Areas where infected animals have been housed should be disinfected with boiling water, steam and/or dilute solutions of bleach or chlorhexidine mixed with water to try and kill infective oocysts. Cleanliness is critical to controlling coccidiosis.
A healthy, well-balanced diet, with regular exercise, free access to fresh water and abundant human companionship, are important to managing infectious diseases. These things are always beneficial to our companion animals.