Giardia lamblia
(intestinalis)
Life
cycle is similar to that of Entamoeba histolytica:
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Images:
Cysts: http://www.k-state.edu/parasitology/625tutorials/Protozoa04.html
Trophozoites: http://www.k-state.edu/parasitology/625tutorials/Protozoa02.html
Phylogeny: Order Diplomonadida
Preferred
definitive host: Humans
Reservoir
hosts: Possibly dogs,
cats, rodents, cattle, beaver
Vector/intermediate
host: None
Geographical
location: Cosmopolitan, but
occurs most frequently
in
warm climates among children.
Organ
affected: Duodenum,
jejunum, and upper ileum.
Symptoms
and clinical signs: Mucus in stools,
diarrhea,
dehydration, intestinal pain,
flatulence, and weight loss.
Treatment: Quinacrine, Metronidazole
Note: European travel agents are advising THEIR
customers who arrange visits to the
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Prevalence of Cryptosporidium spp.
and Giardia intestinalis
in Swimming Pools, Atlanta, Georgia Joan M. Shields; Elizabeth R. Gleim;
Michael J. Beach Emerg Infect
Dis. 2008;14(6):948-950.
©2008 Centers for Disease Control and Prevention (CDC) Posted 06/30/2008
Abstract and Introduction
AbstractCryptosporidium spp. and Giardia intestinalis
have been found in swimming pool filter backwash during outbreaks. To
determine baseline prevalence, we sampled pools not associated with outbreaks
and found that of 160 sampled pools, 13 (8.1%) were positive for 1 or both
parasites; 10 (6.2%) for Giardia sp., 2 (1.2%) for Cryptosporidium spp.,
and 1 (0.6%) for both. Introduction
Giardia sp. and Cryptosporidium spp. are
gastrointestinal parasites spread through the fecal-oral route. In 2003-2004,
these parasites were responsible for 61.2% (Cryptosporidium spp. 55.6%; Giardia
sp. 5.6%) of gastroenteritis outbreaks associated with treated swimming
venues (e.g., swimming pools, water parks) in the United States.[1] Cryptosporidium's key
role in these outbreaks is likely because of its small size, low infectious
dose,[2] and high tolerance to chlorine,[3] which
is the major disinfectant used in swimming pools. Despite frequent outbreaks,
little is known about these parasites' occurrence in swimming pools in the
absence of outbreaks. Although the frequency of contamination is unknown,
4.4% of formed feces recovered from non-outbreak-related pools were positive
for Giardia
sp. and 0 were positive for Cryptosporidium
spp..[4] In the
Netherlands, 7 pools sampled for >1 year had a prevalence of 5.9% for Giardia
sp., 4.6% for Cryptosporidium
spp., and 1.3% for both pathogens.[5] In
Italy, 1 study found 28.6% (2/7) of tested pools were positive for both Giardia
sp. and Cryptosporidium
spp.[6] and another study found 40% (4/10) of tested pools positive for
either parasite.[7] No data exist on the occurrence of these parasites in US pools.
Further data on pool contamination would reinforce existing During
the past 2 decades, Cryptosporidium
spp. and Giardia
sp. have been associated with increasing outbreaks of swimming-associated
gastrointestinal illness in the United States; Cryptosporidium spp. is emerging as the
leading cause of swimming pool-associated outbreaks of gastrointestinal
illness.[1] However, the baseline prevalence of contamination in
non-outbreak-associated swimming pools is incomplete. The Study
A
convenience sample of 160 public swimming pools from 2 metropolitan Atlanta,
Georgia, counties was used to collect filter backwash samples for parasite
examination during a 7-week period (late August-October 2006). Information on
age of swimmers, pool type, pool size, and number of swimmers was gathered.
No facility identifiers were assigned. Filter
backwashing is a cleaning process by which the water flow through the filter
is reversed so that accumulated debris trapped in the filter is dislodged and
directed to waste. Filter backwash therefore tends to contain more
concentrated pathogens than does pool water. All selected pools had a sand
filter (most public pools in the metropolitan One-liter
samples of filter backwash were collected in wide-mouthed plastic bottles
shortly after the filter flow grew turbid and were transported and stored at
4°C before flocculation. The samples were calcium carbonate flocculated
within 2 weeks, typically within a few days, after collection.[8]
Pellets were stored in DNase, RNase-free,
sterile microcentrifuge tubes. DNA was extracted
from 250-350 mg of each pellet by using a FastPrep
DNA kit (MP Biomedical, Real-time
qPCR used the Stratagene
Mx3000P thermocycler (Stratagene,
La Jolla, CA, USA) and the triplex PCR reaction and amplification protocol
described for Entamoeba histolytica,
Giardia intestinalis,
and Cryptosporidium
spp. (primers and probe amplify both C.
parvum and C. hominis) with
a reported sensitivity and specificity of 100%.[9] DNA
from E. histolytica was added to each sample as a positive
internal control. Sample inhibition was alleviated by repeating the qPCR with 4.7 µg/µL of bovine serum albumin (Sigma, Of
the 160 filter backwash samples collected, 13 (8.1%) were positive for 1 or
both parasites; 10 (6.2%) were positive for G. intestinalis;
2 (1.2%) were positive for Cryptosporidium
spp.; and 1 (0.6%) was positive for both pathogen genera. Because of the
small amount of target DNA, speciation was not possible with most samples.
However, 1 C. hominis positive sample was identified. The
Table
1 summarizes parasite prevalence by age of swimmers, pool type,
pool size, and number of swimmers. Although 117 (73.1%) of all pools tested were
commonly used by children (28 were designated for children only, 89 for
children and adults), these pools accounted for 12 (92.3%) of 13 positive
pools sampled. In comparison, 43 (26.9%) of 160 pools designated for adult
use were associated with 1 (7.7%) of 13 positive pools. Of the positive
samples, 10 (76.9%) of 13 were found in community pools, although community
pools accounted for 40% (64/160) of pools assayed. Small-volume pools
(≤50,000 gallons) comprised 72 (45%) of 160 sampled pools but accounted
for 9 (69.2%) of 13 positive samples. Similarly, pools with ≤75
swimmers per week comprised 42.5% of pools but accounted for 10 (76.9%) of 13
positive samples. Although
this study was small and the power low, estimates of the prevalence odds
ratio (POR) were calculated. Those associations that were statistically
significant for finding protozoa-positive samples were as follows: community
pools (POR 5.7, 95% confidence interval [CI] 1.5-21.8) and weekly number of
swimmers of <75 (POR 5.1, 95% CI 1.4-19.4). Although the positive parasite
sample prevalence was higher in pools frequented by children and adults
(10.1%) than in pools designated for adults only (2.3%), the POR was not
significant (POR 4.8, 95% CI 0.6-38.1), likely because of the small sample size. Prior
analysis of 22,131 US pool inspections demonstrated that children's pools had
an increased incidence of critical pool code violations perhaps because their
smaller volumes and depths make maintaining appropriate levels of
disinfectant more difficult.[4,10] In
addition, younger children may be more likely to contaminate recreational
water as a result of being incontinent or having higher levels of perianal fecal contamination.[11] This
finding necessitates greater vigilance in maintaining water quality for this
population because they are more likely to contaminate the water and are more
vulnerable to the severe effects of diarrheal illnesses. Conclusions
This
study is a snapshot of contamination at the end of the swim season. Although
an earlier sampling schedule may have detected more contamination, these
findings suggest that contamination events in some pool types or with some
swimmer compositions may be relatively common during the swim season. The
prevalence of contamination found by this study is difficult to compare with
that found by other studies that focus on serial samples from a small number
of pools. However, the key finding, parasite detection, is repeated in all
the studies cited.[5-7] The risk for disease transmission is
difficult to ascertain because most studies, including this one, have not
measured viability of the parasites recovered from water or filter backwash.
However, intact Cryptosporidium
oocysts observed following hyperchlorination
to inactivate the parasite are commonly noninfectious (M.J. Arrowood, pers. comm.). This
study is limited by having a small sample size, by being a convenience
sample, and by using backwash collected from pools with a single filter
medium (i.e., sand) exclusively. In addition, the sensitivity and specificity
of PCR detection in pool-associated backwash samples is unknown, although
positive and negative controls reacted appropriately. Although these
deficiencies would likely lead to underestimates of the prevalence of
parasites in this sample, clearly such study results are neither generalizable to all types of pools nor an accurate
measure of national contamination levels. However, despite these
deficiencies, the finding of swimming pool filter contamination by Giardia
sp. and Cryptosporidium
spp. is key and reinforces the need for continued
emphasis on improving pool operation and maintenance (e.g., preventive hyperchlorination or flocculation on a routine basis).
These improvements should also include consideration of supplementary inline
disinfection systems known to inactivate Cryptosporidium
spp. (e.g., ultraviolet light, ozone) and other pathogens.[3,12-14] These
data also underscore the need for the general public, particularly immunocompromised persons, to understand recreational
water-associated illness transmission and adopt healthy swimming habits
(e.g., no swimming when ill with diarrhea, no swallowing of pool water,
improved hygiene[15]) that are needed to reduce the risk for pathogen transmission.
Table 1. Pathogen Distribution in 13 Cryptosporidium- and Giardia-positive
Swimming Pools (n = 13)
*G,
Giardia intestinalis;
C, Cryptosporidium
spp.; Ch, C. hominis; CG, both G. intestinalis
and Cryptosporidium
spp.
References
Acknowledgements We
thank the pool operators and managers who took the time to participate in
this study. We also thank Stanley L. Gaines and John Gormley
for their help in locating swimming pools. We especially thank Jacquelin Roberts for help with the statistical analysis. Funding Information This
project was supported by the CDC Foundation through a grant from the National
Swimming Pool Foundation. Reprint Address Joan
M. Shields, Centers for Disease Control and Prevention,
Joan M. Shields,*† Elizabeth
R. Gleim,* Michael J. Beach*
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