Transmission

 

 

Introduction to Transmission

The specific means to transmission are still unresolved.  However, there are some important aspects of transmission which are known.  There are two major types of transmission:  Waterborne and Foodborne.  It is known that transmission of Cyclospora directly from person to person is unlikely because the oocysts that infected persons excrete in their feces is not infectious.  It requires up to 2 weeks for the oocysts to be come infectious, therefore it is unlikely that one infected person directly transmits the parasite to another

person.  Indirect transmission, on the other hand, can occur.  Cyclospora may be transmitted by ingestion of water or food contaminated with oocysts. 

 

Waterborne Transmission

 

The ability of Cyclospora to exist in water depends on whether or not the water source has become contaminated and also the potential for water treatments to kill or remove the oocysts.  It is known that Cyclospora oocysts are highly chlorine resistant.

 

In 1994 in a waterborne outbreak in Nepal, a group British expatriates became ill after drinking out of the military water supply. The water which was partly river and municipal water

had been chlorinated and pumped into tanks beside the houses.  Cyclospora oocysts were found in the chlorinated tanks. 

 

There have been up to three cases of outbreaks caused by contaminated water in the United States.  The first documented case was in 1990 which occurred in a dormitory in Chicago.  Similar to the situation in Nepal, it was a case of contaminated water storage tanks. 

 

Foodborne Transmission

Foodborne transmission of Cyclospora is responsible for a large majority of the publicity of the parasite.  In the 1990s, there have been at least 11 foodborne outbreaks of cyclosporiasis in North America, affecting nearly 3600 people.  Although the incidence of foodborne outbreaks is subject to underrecognition and underreporting, the national outbreaks and publicity is unprecedented for other protozoan parasites.

The following types of produce are most often responsible for the outbreaks:

 

 

Raspberries

Basil

Mesclun

Understanding the epidemiology of transmission is complicated by the fact that by the time the outbreak is recognized by the public health officials it is unlikely that any food from the incident will be left.

 

However, there have been two outbreaks in which raspberries were concretely identified as the responsible agent.  In the spring of 1995, in New York and Florida, Guatemalen raspberries were served at various social events, causing the two outbreaks.  Probably because New York and Florida were already experienced in identifying the Cyclospora oocysts, they were the first to recognize the highly publicized 1996 national outbreak.  The outbreak resulted in 1465 cases that were reported to the CDC as well as the cover of Newsweek.  Raspberries make particularly good transporters of the parasite because of the many crevices and hairs on the berry’s surface.  Additionally, the raspberries are kept cool during transport which probably delays sporulation.  Ironically, it is hypothesized that the berries were contaminated by water when the berries were sprayed with various insecticides and fungicides.

* http://www.journals.uchicago.edu/CID/journal/issues

/v31n4/000497/000497.text.html

This picture indicates the contrast between the surface of a raspberry (left) and a blackberry (right), as viewed by scanning electron microscopy.