Coccidia : The Next Battle for the Fantastic Four Kittens

Coccidia oocysts in a fecal flotation from a c...

Image via Wikipedia - Coccidia in fecal flotation from cat

Yesterday afternoon upon arriving at the hospital and doing one of many sweeps of the front area, I found my favorite kitten quartet missing. I soon found out that they’re with an employee because the poor babies have coccidia.

Scientific Classification

This parasite has a one host life cycle. The Eimeria species has a single host, meaning you can’t infect a cow with chicken coccidia. The Cystoisospera species has also a single host but most can use a paratenic host. Dogs, cats, humans and other carnivore infecting coccidia use 2 hosts in their cycle. Coccidia is extremely host specific. It is also site specific once inside the host. Each species has specific a location in the intestine where it will develop or maybe even a specific part of a cell.

In terms of multiplication, coccidia are sexual OR asexual (schizogony). The sexual multiplication uses macrogamonts (female) and microgamonts (male). Upon fertilization, a zygote is produced that becomes an oocyst.

The oocyst is the environmentally stable cyst stage of the parasite. They are excreted unsporulated and sporulate once in the environment. The particular species of coccidia is identified based on the structure of the sporulated oocyst. Not all species are pathogenic and it is the sporozoites that actively invade cells. Excystation out of the oocyst and sporocyst occurs when the bile and trypsin in the stomach and intestine activate the sporozoites. The Eimeria species has 4 sporocysts with 2 sporozoites each while the Cystoisospera have 2 sporocysts with 4 sporozoites each.

This parasite follows a fecal-oral transmission (i.e. ingesting something contaminated by infected fecal material). This parasite is important in industries such cattle, poultry and swine. Pathogenicity (how severe the infection is) can depend on many factors such as:

  • Species of coccidia
  • Number of occysts ingested
  • Age of animal
  • Presence of immunosuppression
  • Environmental conditions

The disease may result in:

  • Diarrhea
  • Weight loss
  • Tissue destruction by rupture of infected cells (merozoites released)
  • Vilous atrophy – malabsorption
  • Hemorrhage – blood loss
  • Death

Hopefully the kittens aren’t too heavily infected and will recover soon.

:: Information from this post is from my notes from an Introductory Parasitology class taught by Dr. Zajac at Virginia Tech ::


The Stages of Toxoplasma gondii

T. gondii constructing daughter scaffolds with...

Image via Wikipedia

As stated in Toxoplasma gondii, today I’m going to break down the stages of the parasite. Those stages are:

  • Sporulated oocysts (sporozoites) from environment
  • Tissue cysts containing bradyzoites in raw/undercooked meat
  • Tachyzoites in tissues
  • Entero-epithelial stages (only in cats)

Oocysts are produced non-sporulated but will sporulate in about 2 days. They are about 10×10 µm and millions can be produced within days. Cats can develop strong immunity to this stage.

In the intermediate host, the life cycle is as follows:

  • Excystation of sporozoites
  • Sporozoites –> Tachyzoites
  • Tachyzoites disseminate infection and eventually become bradyzoites or tissue cysts
  • Latent infection
  • Endodyogeny (a form of sexual reproduction)

Tachyzoites have a fondness for neural and cardiac tissue but can infect any nucleated cell in the body. This is the stage that crosses into the placenta and causes congenital infections. Rapid division of tachyzoites is what causes tissue destruction, the spread of infection and lesions.

Bradyzoites (“brady” = slow) are responsible for tissue cysts. They can be present in any organ and survive for the life of the infected animal since they are resistant to the drugs used to treat Toxoplasmosis. If the host is immunocompromised, infection can be reactivated and intermediate hosts can infect one another. Bradyzoites are at fault for initiating meat induced infection, on top of being the only stage to give rise to entero-epithelial stages.

Once again, the etero-epithelial stages are only found in cats. There are 5 types of entero-epithelial schizonts (which will not be listed). This is where the sexual stages/oocysts are produced.

Overall, Toxoplasma gondii was the most successful parasite discussed in my Intro Parasitology course.

:: Information from this post is from my notes from an Introductory Parasitology class taught by Dr. Zajac at Virginia Tech ::