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Coccidiosis In Rabbits – Part Two

Coccidiosis. If you’ve been learning about rabbits more than about two minutes you’ve heard of it.

And, if you believe everything you’ve read, you’re probably terrified. Well, don’t be. Once you understand the parasite, you’ll see that while it IS a serious concern, it can be controlled.

To begin, let’s talk about what coccidia actually are. I’ll say this again in case you missed it in Part One – there will be some complicated, science-ish terms used in this section, so I will break them down a bit. I’m not assuming you can’t understand the technical lingo, I just want to be sure you 100% know what I’m talking about.

Coccidia are microscopic, single-celled “obligate intracellular parasites.”

An “obligate intracellular parasite” absolutely MUST be inside an animal cell to live and reproduce. I want to repeat this: inside an animal CELL. That’s important to understand because you’re not going to SEE coccidia like you might see roundworms (the long spaghetti-like parasites puppies will often pass after their first worming..yes, rabbits can get those too!). They are absolutely microscopic at all stages.

There are literally thousands of types of coccidia, but the beauty of them is that they are almost always species specific. Almost (there are some that will infect species other than their normal host, even humans). The genus that WE are concerned about with rabbits is Eimeria.

According to the Merck Veterinary Manual, 11th Edition, the following are the most common species that affect rabbits (this is not ALL of the species that affect rabbits, just the most common):

E stiedae

E magna

E irresidua

E media

E perforans

E flavescens

E intestinalis

All of the Eimeria species undergo essentially the same process that turns them from non-infectious eggs to disease causing, active parasites. Here’s how it works:

Oocytes are the coccidia eggs, and those are the only form that can survive OUTSIDE the cell of an animal host. They have a thick, tough “shell” that protects them from…well, everything.

When they are first released into the environment in the rabbit’s feces, they are not infectious – in fact, you can think of them sort of like a chicken egg at first. All the material is there to make the parasite, but it has to go through some processes to be a problem.

Sporulation is an asexual form of reproduction of many protozoans, also known as meiosis. As soon as the coccidia eggs enter the environment, the presence of oxygen and moisture que the process of cell division known as sprorulation. For those who already know the term meiosis, sporulation IS meiosis (which, for those who don’t know, is a process of cell division which produces reproductive cells and makes sexual reproduction possible).

Through meiosis, four sporocysts form, and then inside of those sporocysts, two sporozoites form. In the end, after 24 hours to seven full days (depending on the Eimeria species), each coccidia egg contains eight sporozoites. That oocyte is now called a sporulated oocyte, and it is infectious.

So now, one egg has turned into eight infectious….parts. Let’s call them that for now. Then, along comes your rabbit and ingests just one of those sporulated oocytes (infectious eggs). How does that happen?! Well, it’s pretty simple – anything that feces has even TOUCHED can have oocytes on it.

I don’t know about you, but I’m always cleaning water bowls because there’s a floater in there (how does a 14 pound doe fling poop into her water bowl  EVERY DAY?!), or I’m digging little baby turds out of feeders because as soon as I take away nest boxes the WHOLE litter has to try to sleep in the j-feeder.

So, we clean waterers and feeders pretty regularly, right? Well, sort of. See, oocytes are NOT killed by just soap and water. Bleach doesn’t kill them, air doesn’t kill them, sun doesn’t kill them, the friction of scrubbing doesn’t kill them….there are only two things that are proven to work without fail….fire and a 10% ammonia solution.

I certainly don’t torch my rubber water bowls every day, and I don’t scrub them with 10% ammonia solution every day either, so even though I don’t SEE any contamination, it’s still there. And that’s not even considering resting mats, floor wire, nest boxes, the rabbit itself (feet, nails, and fur), or the scoop I use to feed that has surely fallen to the floor a hundred times just this week, etc.!

So, your rabbit has ingested a sporulated oocyte. Crap, now what?!

Once the oocyte reenters the digestive system, it’s shell begins to break down. By the time it leaves the stomach, the oocyte has opened up and the four sporocysts have been released, and they too have opened releasing the total of eight sporozoites into the duodenum (the very first part of the small intestine, just after the stomach).

Those eight sporozoites then travel through the intestine to the part that their particular Eimeria species infects. While it has not been totally determined for every single Eimeria species exactly HOW they know where to go, it’s thought that each species has membrane-bound structures on their surface that release secretions that are then recognized by the host cell’s receptors – until the sporozoites reach those cells and their secretions are recognized, they just glide along inside the intestine. The host cell receptors then recognize the secretions and draw the sporozoites to the cell like a magnet.

Once the sporozoites reach the host cells, they invade them and start feeding. At this stage, they are called trophozoites.

I really want you to remember this part – trophozoites are the initial feeding stage of the coccidia parasite, and it develops AFTER the cell is already invaded. Got it? Great!

Once the trophozoite has fed, the process of schizogony begins. Schiz  WHAT?!

Schizogony is an asexual form of reproduction where the nucleus of the trophozoite divides by mitosis into two identical nuclei. At this point, the trophozoite is now called a schizont. The process of mitosis continues over and over again, resulting in potentially thousands of nuclei inside of each schizont.

So let’s slow down just a second and go over this all again real quick!

  1. An oocyte is expelled with the feces of the rabbit.

  2. At some point between 1 and 7 days later, the oocyte has sporulated and now contains 8 sporozoites, and is now infectious.

  3. The rabbit consumes the infectious oocyte, which bursts open and releases the 8 sporozoites.

  4. The sporozoites float along in the intestine of the rabbit until the magnet-like host cell receptors pull them close. All 8 sporozoites invade separate host cells (each oocyte ingested initially results in eight infected cells).

  5. The sporozoites begin feeding on the hosts nutrients and are called trophozoites.

  6. Once trophozoites finish feeding, they begin reproducing by dividing their nucleus and making two identical ones; each of those two nuclei divide as well, and so on and so forth from two to seven generations depending on species. After the very first nucleus divides, the sporozoites are not called trophozoites anymore, they are called schizonts.

Each nuclei within the schizont becomes a merozoite, which is a new cell in and of itself. The schizonts eventually burst due to the number of merozoites, which kills the host cell they were in and releases all of those potentially thousands of merozoites into the intestine.

The now free merozoites do one of three things….they either invade a new host cell and begin reproducing again into more merozoites, or invade a new host cell and become either macrogametes (female reproduction cells) or microgametes (male reproduction cells).

When some of them become male and female gametes, the parasite is now capable of sexual reproduction (all stages before this have been asexual). A male and a female gamete then come together and form an oocyte. That new oocyte is then passed through the intestine in the feces and the process starts all over.

To recap one final time:

  1. one single sporulated oocyte led to eight infected intestinal wall cells.

  2. Those eight cells hosted potentially thousands of merozoites EACH until the number of merozoites caused the cell to rupture and die.

  3. Each of the merozoites released by that now dead initial host cell go on to invade their own, new host cell.

  4. Some of those merozoites continue to reproduce and create thousands more merozoites, some become female gametes and some become male gametes.

  5. One male and one female gamete come together and create an oocyte which is passed out of the rabbit, and begins the process all over again.

Now, the scary part. A rabbit ingests potentially thousands of oocytes every day. If enough sporulated oocytes are ingested, of the more serious species, and enough damage is done, you may see signs of the disease we call coccidiosis.

Some rabbits never show ANY signs. Ever. They don’t get sick, they don’t go off feed or lose condition, and they appear completely, totally normal. But, they still shed oocytes into the environment. Other rabbits get very ill, very quickly, and before you can do much to figure out what exactly is wrong, they are dead.

Here is a list of the prepatent periods (the time from ingestion of an oocyte to the production of new ones inside the rabbit)  for each of the above, and a graphic showing the location in the digestive tract where each species reproduces.

Click to enlarge

E stiedae       PP: 14 – 18 days

Sporulation: 3 days

Symptoms:    In mild cases of liver coccidiosis (this is the only species known to infect the liver) there may be no signs, but in more severe ones the animals lose their appetites and grow thin. There may be diarrhea, and the mucous membranes may be jaundiced. The disease is more severe in young animals than in old. It may be chronic, or death may occur in 21 to 30 days.

Some of the symptoms are due to interference with liver function. The liver may become really big, and white to yellowish bumps or strings appear in it. At first they are well defined…an obvious round bump for example, but later as they get larger and there are more of them, they are harder to tell one from the other. The enlarged bile ducts are filled with the developing parasites. Under a microscope,you will see a massive enlargement  of the bile duct epithelial cells. Instead of forming a simple, narrow tube, the epithelium is thrown into big, tree-like folds, and each of those epithelial cells contains a parasite.

E magna       PP: 6 – 8 days

Sporulation:  2 – 3 days

Symptoms:    The principal signs are loss of weight, lack of appetite and diarrhea. A good deal of mucus may be passed. The animals lose their appetites and grow thin. The intestinal lining has decreased blood flow and is inflamed, and epithelial sloughing may occur.

E irresidua    PP: 9 – 10 days

Sporulation: 2 – 2.5 days

Symptoms:    This is one of the more pathogenic of the intestinal coccidia of rabbits. This is a BAD one. It causes the usual signs of intestinal coccidiosis. The affected areas of the intestine have a decreased blood flow, there may be leaking of blood from the intestinal lining, and the epithelium may slough and become denuded.

E media         PP: 4.5 – 6 days

Sporulation: 2 days

Symptoms:    It may cause the usual outward signs of intestinal coccidiosis such as watery, blood streaked, or mucous-laden diarrhea. The affected parts of the intestinal lining may be swollen, with greyish spots.

E perforans  PP: 5 – 6 days

Sporulation: 2 days

Symptoms:    E. perforans is one of the least dangerous intestinal coccidia of rabbits, but it may still cause mild to moderate signs if the infection is heavy enough. The duodenum may be enlarged by edema (fluid in the tissues), sometimes chalky white in color; the jejunum and ileum may contain white spots and streaks, and there may be small areas of broken bloodvessels the cecum.

E flavescens            PP: 7 – 9 days

Sporulation: 4 days

Symptoms:    Often presents dually with E intestinalis, so symptoms and necropsy findings are similar.

E intestinalis            PP: 9 days

Sporulation: 2 days

Symptoms:    According to Pellerdy (1953, 1954), experimental infections with this species cause more or less severe intestinal inflammation and diarrhea, and may kill young rabbits. At necropsy, edema and greyish-white foci which may come together to form a, sticky, pus- like layer  in the intestine.

I’ve given you a LOT to think about and absorb, I know. In the next, and final part, I’m going to discuss various prevention and treatment protocols at some depth, using the most recent information I can get my hands on. I’ll include ways to clean and sanitize your rabbits environment, as well as specific products used to treat and prevent the parasite in rabbits.

In the mean time, what I’d like for you to do is carefully consider whether you would be willing to use medications, including antibiotics, to deal with this problem should is present in your rabbitry. There are of course advantages, and disadvantages, both ways so give it very careful consideration.

I’ll have Part Three available for you very soon!

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