Cyclospora Information from those who Identified It

Ron Taylor ron.taylor at ketchum.com
Tue Jun 25 12:44:45 EST 1996

Dr. Charles Sterling, Department of Veterinary Science, University of Arizona

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 

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.

More information about the Microbio mailing list

Send comments to us at biosci-help [At] net.bio.net