Environmental Engineering Reference
In-Depth Information
The “411” on Cyclospora
The CDC (1998) described
Cyclospora cayetanensis
as a unicellular para-
site previously known as cyanobacterium-like (blue-green algae-like) or
coccidia-like body (CLB). Since the first known cases of illness caused by
Cyclospora
infection were reported in the medical journals in the 1970s, cases
have been reported with increased frequency from around the world, in part
because of the availability of better techniques for detecting the parasite in
stool specimens. The transmission of
Cyclospora
is not a straightforward pro-
cess. When infected persons excrete the oocyst state of
Cyclospora
in their
feces, the oocysts are not infectious and may require from days to weeks
to become infectious (i.e., to sporulate). Transmission of
Cyclospora
directly
from an infected person to someone else is unlikely; however, indirect trans-
mission can occur if an infected person contaminates the environment and
oocysts have sufficient time, under appropriate conditions, to become infec-
tious.
Cyclospora
, for example, may be transmitted by ingestion of water or
food contaminated with oocysts. Outbreaks linked to contaminated water,
as well as outbreaks linked to various types of fresh produce, have been
reported in recent years (CDC, 1997a,b; Herwaldt et al., 1996; Huang et al.,
1995). How common the various modes of transmission and sources of infec-
tion are is not yet known, nor is it known whether animals can be infected
and serve as sources of infection for humans.
Persons of all ages are at risk for infection. Persons living or traveling in
developing countries may be at increased risk, but infection can be acquired
worldwide, including in the United States. In some countries of the world,
infection appears to be seasonal. The incubation period between acqui-
sition of infection and the onset of symptoms averages a week.
Cyclospora
infects the small intestine and typically causes watery diarrhea, with fre-
quent, sometimes explosive stools. Other symptoms can include loss of appe-
tite, substantial loss of weight, bloating, increased flatus, stomach cramps,
nausea, vomiting, muscle aches, low-grade fever, and fatigue. If untreated,
illness may last for a few days to a month or longer and may follow a remit-
ting-relapsing course. Some infected persons are asymptomatic.
Identification of this parasite in stool requires special, not routine, labo-
ratory tests to be done (discussed later). A single negative stool specimen
does not rule out the diagnosis; three or more specimens may be required.
Stool specimens should also be checked for other microbes that can cause a
similar illness. TMP-SMX has been shown in a placebo-controlled trial to be
effective treatment for
Cyclospora
infection (Hoge et al., 1995). No alternative
antibiotic regimen has been identified yet for patients who do not respond to
or are intolerant of TMP-SMX.
Based on currently available information, avoiding food or water that may
be contaminated with stool is the best way to prevent infection, and reinfec-
tion can occur.
