Hideous under the microscope, they loom large; and they're on the warpath! Intestinal parasites, Cyclospora cayetanensis, look like colossal, blood-red cysts swimming in a swirling, globulous sea of blue-green algae. Not only are they monsters in a microscopic universe, but they are also the nemesis of globetrotters and one of the culprits in what's known as "Traveler's Diarrhea," protracted, relapsing gastroenteritis acquired by ingesting contaminated food or water. Recognized as an emerging pathogen, the opportunistic parasite cyclospora not only affects people worldwide with a disease known as cyclosporiasis — it's also been diagnosed in dogs.
With a short recorded history, cyclospora gained medical attention with the first three human cases of cyclosporiasis in 1977 and 1978, but it wasn't formally characterized or named until 1994. Associated with travel, it primarily affected people who visited developing countries in the 1970s and 1980s. But since the 1990s, outbreaks in North America have also been linked to imported contaminated raspberries, strawberries, lettuce and herbs. As recently as 2017, there was a major spike in the infection in humans in the U.S. and Canada. Still, no definitive source can be established. So how in the world do dogs get infected with cyclospora? And why is there so little information about the canine version of the infection available?
The history of cyclospora in dogs.
Rich in architectural and cultural tradition, vibrant São Paulo, Brazil holds the distinction of being the most populous city in the Southern Hemisphere — and the place where the first two cases of cyclospora in dogs were discovered; the first in 1995, the second in 1996. Around the same time in the U.S., an outbreak of cyclosporiasis was taking its toll on people who didn't even have to leave home to acquire it. Although there are several species of cyclospora, the strain responsible for the South American dogs' infections was cayetanensis, the same as in human cases of the disease. Back then, in the early days of the disease, the seeds of suspicion were planted — was cyclospora zoonotic, that is, able to be transmitted from dogs to people? Decades later, there is still little proof either way, and research unearths scant statistical data on the infection in dogs.
So, as cyclospora emerges, perched on the horizon of parasitic abominations, and rapidly becoming mainstream, it has wrestled with an identity crisis since first coming to light. And although it's undergone extensive studies in humans, the protozoan is still described by the medical community as obscure, confusing, and enigmatic. Often mistaken for other parasites such as cryptosporidium, especially in the early days, this parasitic organism is confounding because, in the world of pathogenic disease, it is so new. Over the years, time-consuming and labor-intensive testing has been replaced by polymerase chain reaction (PCR) in the 1980s that detects the DNA sequence of organisms, and other more recent technologically advanced diagnostics can pretty much nail down when it's cyclospora. At this stage, it seems that humans are the main reservoirs of the parasite with limited evidence in other animals, including dogs.
As for the incidence of the infection in dogs, it seems virtually lost in space with no definitive collection of data. But, like other coccidias, it's infectious only in its sporulated form which occurs under specific environmental conditions outside the body after being excreted in the stool. It takes from seven to 20 days to percolate and become infectious. And like other numerous genera of coccidia that infect dogs, these microscopic protozoans spend part of their life cycle in the lining cells of the upper small intestinal tract.
Cyclospora modus operandi and how will I know if my dog is infected with cyclospora?
You can't spot them with the naked eye, but tiny cyclospora appear cyst-like, spherical and ominous beneath the magical lens of a microscope. Single-celled or unicellular cyclospora are members of a nasty family of organisms that must live and reproduce in an another animals' cells to survive, causing not only cyclosporiasis but other coccidia-based diseases such as coccidiosis, cryptosporidiosis and toxoplasmosis.
While this particular genus, Cyclospora cayetanensis, lacks sufficient background in canine infections, it is a coccidia and as such is spread through feces. Moreover, it shares the same MO as other coccidias, for example, Isospora, the most common in dogs_,_ which indicates the same or similar symptoms can be expected. Namely, the following symptoms in-common may be observed in puppies —susceptible due to their immature immune systems — and old, debilitated, or immunosuppressed mature dogs:
- Severe, watery diarrhea.
- Abdominal distress.
- Distended abdomen.
- Weight loss.
Harking back to the well-documented cases of the first two dogs ever diagnosed with a cyclospora infection in the 1990s, the first was a 4-month-old husky pup who experienced watery diarrhea for a 20-day period along with vomiting, loss of weight and lethargy. In the second case, a 1-year-old Rottweiler had a five-day history of watery diarrhea, dehydration, anorexia and abdominal sensitivity. Both young dogs were subsequently treated with antibiotics such as Tinidazole and fully recovered from the infections.
Keep in mind that most coccidia-caused infections are sub-clinical and have no observable symptoms in healthy dogs.
Diagnosis of cyclospora infection in dogs and treatment protocol.
Your veterinarian will review your dog's medical history, ask you questions about the symptoms you may have observed, and where you think the infection was acquired, and he'll perform a thorough physical examination. Remember to take a stool sample along with you to the vets.
A coccidia infection will ultimately be diagnosed via a microscopic examination of a stool sample. Oocysts of coccidia are much smaller than the eggs of intestinal worms, so fecal zinc sulfate solution aids fecal evaluations. Infection with some of the less common coccidial parasites such as cyclospora may also be diagnosed with a blood test.
How is the coccidial infection cyclosporiasis treated?
Fortunately, coccidial infections such as those from cyclospora are self-limiting and in healthy dogs require little medical intervention. Sulfa-type antibiotics, such as sulfadimethoxine are typically administered for five to 20 days. Severe infections may require repeated or longer-term treatment. However, reinfection may be an issue, particularly in a dog with coprophagia who consumes his stools.
Is there any way to prevent cyclospora infections in my dog or get rid of the parasites in and around my home?
You can reduce the chances of your dog picking up cyclospora or any other coccidial parasite by removing feces as quickly as possible from your yard to prevent reinfection. Inside, steam cleaning rugs will destroy oocysts. For floor areas and other surfaces, you can use diluted chlorine bleach to eliminate the parasites — one cup of bleach in one gallon of water will work, but be sure to test the solution in a small area first since bleach can also damage surfaces.
Can I get cyclosporiasis from my dog?
You may be wondering if you can pick up cyclosporiasis from your dog. The answer is — there's no definitive proof, as of 2018, that cyclosporiasis is a zoonotic disease (transmissible from animals to humans). However, one of the parasite's cousins, cryptosporidium, is zoonotic. On the other hand, isospora, the most common coccidia found in dogs is not transmissible to humans. From all accounts, it seems that dogs are not vectors of the disease.
Bottom line, the most common coccidias are not infectious to humans, but oddball parasites like cryptosporidium are. And cyclosporiasis, an emerging pathogenic disease, has a long road ahead before it's fully understood. It makes good sense to be a little more cautious if your dog is recovering from an intestinal parasite infection if you are:
- A pregnant woman.
- A cancer patient who is undergoing chemotherapy or radiation therapy.
- An older adult.
- A person with a chronic disease or a congenital immune system deficiency.
- A person who has received an organ or bone marrow transplant.
- American Society for Microbiology: Update on Cyclospora cayetanensis, a Food-Borne and Waterborne Parasite
- Wonder How To: CDC Warns About a Big Spike in Cyclospora Infections
- Scielo: The First Two Cases of Cyclospora in Dogs, São Paulo, Brazil
- U.S. National Library of Medicine: Cyclospora cayetanensis: A Review of an Emerging Parasitic Coccidian
- U.S. National Library of Medicine: Detection of Cyclospora cayetanensis in animal fecal isolates from Nepal using an FTA filter-base polymerase chain reaction method.
- Revival Animal: Coccidia in Dogs and Cats