CYCLOSPORA: A RECENTLY DISCOVERED PARASITE
Dr. Charles Sterling, Department of Veterinary Science, University of Arizona
Overview
Public health officials are seeking the cause of a recent outbreak of Cyclospora
cayetamensis, a protozoan parasite. The microbe can cause cramping, abdominal pain,
severe diarrhea, nausea, fever and extreme fatigue; it is treatable with antibiotics
sold as Bactrim or Septra, and is generally not fatal. A number of fresh fruits and
vegetables have been suggested as a carrier, but, at this point, there is no compelling
evidence and no common thread that can point to any cause.
What is Cyclospora?
Cyclospora, once thought to be linked to blue-green algae, has been identified as a new
protozoan parasite and is a relative of Cryptosporidium. Whereas Cryptosporidium can be
transmitted from one infected human to another human, Cyclospora requires a period of
time to work into the environment and must be ingested. Based on our research, we are
certain humans are most likely infected through ingestion of water containing the
infectious stage of the parasite, commonly called the oocyst stage. Once acquired, it
takes from four days to a week before signs of infection are noted. The infection may
last anywhere from one to four weeks. People who are immune compromised are at greater
risk, and therapeutic intervention is required. Strong evidence indicates that humans
are the only likely host of Cyclospora.
Epidemiology of Cyclospora
After 20 years of research, we are starting to define the epidemiological link of
Cyclospora to water. In Nepal, the organism was actually detected in water.
Cyclospora passes from an infected individual in unsporulated (immature) state and
requires one to two weeks time under ideal conditions to become infectious. Ideal
conditions which lead to Cyclospora becoming infectious include exposure to moisture and
temperatures of at least 25 degrees C,(77 to 89 degrees F). A moist environment is
necessary for the organism to sporulate, and become infectious.
Identifying Cyclospora
Cyclospora is an extremely difficult organism to identify, which may account for some of
the problems in pinpointing a cause of the illnesses recently observed. Without
confirmation, it is difficult to be sure that we are, in fact, confronting a Cyclopspora
outbreak in all instances. The most important element in the identification is an
attempt to sporulate the organism in order to see the defining characteristics of the
infectious stage. One must look at the internal structure of the oocyst after it
sporulates, and only then can one be 100 percent certain that the organism is
Cyclospora. If it turns out that some of the outbreaks have been caused by another
parasite, the ability to determine the source of the contamination will be severely
compromised.
Can Cyclospora be spread by food?
It is highly unlikely that fruits or vegetables could be the primary source of infection
in terms of growing or shipping practices. They would literally have to be grown in
human fecal waste and exposed to direct surface contact. It is also unlikely that the
organism can be transmitted from infected food handlers because if their hands were
contaminated with feces, the organisms would still be in an unsporulated and immature
stage. Cyclospora would still need up to two weeks to become infectious.
Virtually every past outbreak has occurred near water, whether it was a lake, a
reservoir tank on the top of a building or a cellar contaminated with sewer water.
At this point in the investigation, of the current outbreaks it is premature to
hypothesize about any specific food as a possible carrier of the parasite. In fact,
such speculation could compromise ongoing investigation.
*Dr. Sterling and his colleague, Dr. Ortega are credited with identifying the Cyclospora
parasite and determining its maturation process. His team is recognized as among the
foremost authorities on the parasite.
