Content uploaded by Lief Erikson Diocampo Gamalo
Author content
All content in this area was uploaded by Lief Erikson Diocampo Gamalo on Mar 17, 2018
Content may be subject to copyright.
Eco. Env. & Cons. 23 (4) : 2017; pp. (1945-1951)
Copyright@ EM International
ISSN 0971–765X
*Corresponding author’s email: vvpaller@up.edu.ph
Prevalence of Cryptosporidium and Giardia in
selected recreational pools in Calamba, Laguna,
Philippines
Vachel Gay Paller*, Paulo Miguel Kim, Moses Edric Abadilla, Anna Monica Bordado,
Michael Galapon, Lief Erikson Gamalo and Constance Aurelle Macalinao
Parasitology Research Laboratory, Animal Biology Division, Institute of Biological Sciences
College of Arts and Sciences, University of the Philippines Los Baños 4031 Laguna, Philippines
(Received 17 April, 2017; accepted 20 July, 2017)
ABSTRACT
Water-borne protozoan parasites, (i.e. Cryptosporidium and Giardia), have received considerable attention
over the past few years because of their role as ubiquitous etiological agents of diarrhea and other related
diseases of humans and animals. Cryptosporidium oocysts and Giardia cysts have been found in water samples
collected from selected pools in Calamba, Laguna, Philippines. Though differing in terms of density between
different pools, Cryptosporidium has been found in all 12 pools (34-2600 oocysts/L) while 10 pools were
found to be positive for Giardia (67-700 cysts/L). Analysis of the physico-chemical parameters (temperature,
pH, conductivity, DO and pool volume) has shown no significant effects on the densities of both parasites.
Private pools were found to have the higher parasite density and prevalence. Children’s pools similarly
showed greater parasite contamination compared to adult pools. Correlation of parasite density and
prevalence with potential contamination factors (e.g. presence of animals, pool protocols, mixed pool use
etc.) derived from pool interviews showed no significant relationship between the two. However, qualitative
assessment of the study areas revealed that pools with the highest parasite densities were characterized by
low adherence to pool regulations.
Key words: Giardia, Cryptosporidium, Recreational pools, Immunofluorescence assay, Calamba, Laguna, Philippines
Introduction
Protozoan parasites are a medically important
group in studies of water-borne pathogens and are
known to cause diarrhea-like diseases. Contami-
nated waters which come into contact with humans
pose as a potential health hazard, particularly in fre-
quently visited recreational pools. Among these
protozoan parasites are two species which are con-
sidered as the primary cause of waterborne diarrhea
in environmental and recreational waters:
Cryptosporidium (Phylum Apicomplexa) and Giardia
(Phylum Sarcomastigophora). Cryptosporidium is a
coccidian parasite which causes the diarrheal dis-
ease known as cryptosporidiosis (CDC, 2015a). Oo-
cysts of Cryptosporidium are approximately 5 um
small and are the transmission form of the parasite.
Oocysts are capable of surviving in the environment
for periods of up to two years. According to Carey et
al. (2004), this form of the parasite is difficult to re-
move from water as it can pass through conven-
tional filters and are resistant to common water dis-
infectants such as chlorine. Therefore, it is easily
transmitted in contaminated mediums such as
drinking and pool waters. Furthermore, infection
may occur from ingestion of as few as two oocysts
1946 Eco. Env. & Cons. 23 (4) : 2017
among immunocompromised individuals. Giardia is
another protozoan parasite capable of causing diar-
rhea (i.e. giardiasis). Similar to Cryptosporidium, Gia-
rdia is tolerant to common water disinfectants and is
transmitted zoonotically or between humans
through exposure and ingestion of contaminated
waters (CDC, 2015b). Similarly, it passes through
the conventional systems used in water filtration of
pools and drinking water. As few as 10 Giardia cysts
are capable of causing diarrhea (Gardner and Hill,
2001).
In the Philippines, data on both parasites are lim-
ited and have often addressed contaminations from
stools of farm animals (Rivera et al., 2009; Natividad
et al., 2008) and of different bodies of water. The
study by Onichandra et al. (2014), for instance, rep-
resents one of the few expansive examinations of
Cryptosporidium and Giardia in different types of
water samples from the Philippines. However, their
study does not elaborate on the contamination of
recreational waters such as those found in swim-
ming pools. Considering the frequency of these loca-
tions as leisure areas, particularly in some localities
like Calamba during the summer, it is a vital field of
investigation which has far reaching consequence on
the future of health and tourism of the locality. Thus,
the objectives of this study are to detect the presence
of Cryptosporidium and Giardia in selected pools, to
compare their prevalence and density and to deter-
mine various factors that could contribute to the
contamination of these pools.
Materials and Methods
Study Site and Collection of Water Samples
The study was conducted in Brgy. Pansol, Calamba,
Laguna (N 14°11’43" E 121°10’19"). Calamba is a lo-
cality with 54 barangays and 9 sitios and is known
as the “Resort City of the Philippines” due to its
numerous resorts and pools, totaling up to 700 re-
sorts in the area (City Government of Calamba,
2015).
Twelve pools (6 private and 6 public pools) were
selected. Each pool type (public or private) con-
sisted of three adult pool (>40 m3) and three
children’s pool (≥40 m3). One hundred liters of wa-
ter samples were collected from the adult pools
while 50 liters were collected from the children’s
pool. Physico-chemical parameters of the water
samples were measured, such as pH (pH meter:
Milwaukee Instruments Inc, USA), temperature,
conductivity (conductivity meter: YSI Incorporated,
USA) and dissolved oxygen (DO) levels (DO meter:
YSI Incorporated, USA).
Additional data on pool parameters (i.e. source of
pool water, sampling point, and swimming pool
structure and volume capacity) were recorded. Sur-
vey on pool practices and conditions was conducted
at each pool. Three replicates were randomly col-
lected from each three sampling points with refer-
ence to the length of the pool. Pre-sterilized 10 L
polyethylene bottles were used for collecting water
samples (ALS Environmental Limited, 2014). Mem-
brane filtration was performed in situ using a flat-
bed membrane system. Samples were stored in 4°C
and were processed as soon as possible.
Processing and Detection of Cryptosporidium and
Giardia from Water Samples
Detection was performed through immunofluores-
cence assay using a Crypto/Giardia CEL staining kit
(Cellabs Pty Ltd, SYD, Australia) for identification of
Cryptosporidium oocysts and Giardia cyst and evalu-
ated using an epiflourescent Olympus DP70 digital
microscope (Olympus America Incorporated,
Melville, NY, America). Identification was based on
the shape (round, oval and ellipse) and size (2–6 μm
for Cryptosporidium and 8 to 14 μm for Giardia) of
bright green fluorescing bodies. The number of de-
tected oocyst/cyst per liter was noted (Fig. 1) and
calculated to obtain the quantity of oocyst/cyst per
liter.
Statistical analysis
Statistical treatments were performed using IBM
SPSS Statistics program (IBM® SPSS® Statistics
2016, Version 24.0). Prevalence (%) and density (oo-
cyst/cyst per L) of contamination were calculated
for each pool. Pearson correlation analysis was used
to establish the relationship between physico-chemi-
cal parameters and mean densities of
Cryptosporidium and Giardia. Normality of the
samples was ascertained using Shapiro-Wilkes Nor-
mality Test. Significance between the densities of the
parasite and the pool type (private and public) and
pool size (adult and children) was established using
paired t-test (parametric samples). Significance of
the prevalence of both parasites with the pool type
and size was established using Chi-square good-
ness-of-fit test. Survey of the pools was described
qualitatively and was correlated with the parasite
PALLER ET AL 1947
densities using point-biserial correlation. Test results
were considered significant if p<0.05. Graphs were
constructed using Sigma Plot 10.0 (Systat Software,
San Jose, CA).
Results and Discussions
Prevalence and Mean Density
Twelve random samples were collected (6 adult and
6 children pools) from Calamba and tested for
Cryptosporidium oocyst and Giardia cyst. Though
densities were found to differ considerably between
the twelve pools (Table 1), Cryptosporidium and
Giardia were both found to have the highest mean
density in both private (34 - 2,600 oocyst /L and 0 –
700 cyst/L) and children’s pool (34 - 2,600 oocyst/L
and 0 - 567 cyst/L). Cryptosporidium was shown to
be 100% prevalent in all pool types and pool sizes.
Giardia was found to have a higher prevalence
(83.33%) in private pools and children pools than in
Fig. 1. Cryptosporidium oocysts (A) and Giardia cyst (B) collected from swimming pool water samples in
Pansol, Calamba, Laguna
Table 1. Summary of mean physico-chemical parameters and density of Cryptosporidium and Giardia in selected
recreational pools.
Pools Type Size Mean
Temperature pH Conductivity DO Volume Parasite density
(oC) (pH) (µS/cm) (mg/L) (m3)(oocysts/L) (cysts/L)
1 Private Adult 32.17 7.4 1300 0.9 83.4 67 0
2 Private Adult 33.83 6.97 1400 0.7 78.5 34 534
3 Private Children 33 7.13 1400 1.73 11.83 34 567
4 Public Adult 33.93 7.2 1273.33 0.53 376.15 67 0
5 Public Children 32.67 7.3 683.33 0.37 35.17 100 267
6 Private Adult 33.67 7.03 1200 0.68 59.59 634 134
7 Private Children 30.83 7.03 1100 0.6 2 2600 700
8 Public Adult 34.17 7 1300 0.9 121.5 200 267
9 Private Children 32.5 7.87 550 0.1 5.32 300 67
10 Public Adult 32 7.73 1000 0.1 152.64 167 267
11 Public Children 38.5 6.8 1200 0.1 36.28 34 0
12 Public Children 32.83 7.17 900 0.1 23.08 34 134
1948 Eco. Env. & Cons. 23 (4) : 2017
public and adult pools (66.67%). In total, 100% of
both adult and children pools (private and public)
were found to be positive with Cryptosporidium
while 75% of all pools were found contaminated
with Giardia (Fig. 2).
old to harbor and transmit enteric protozoa from
perineal fecal contamination (Gerba, 2000). The
water volumes of both pools similarly act as a factor
to the discrepancy between pools. Though similarly
determined to be statistically insignificant, the
comparison between parasite densities of private
and public pools show that private pools in general
have higher densities and prevalence of both Giardia
and Cryptosporidium. In the case of Pansol, most
private pools are often used exclusively by the
renters and are often not monitored by the owners
and caretakers. Observations in some pool sites
confirm the presence of litter and other domestic
debris in the water, which may account for some
degrees of contamination.
A major factor which affects the contamination of
the pools is largely connected to the general
implementation of pool regulations. According to
the participants of the survey, pools (either adult or
children’s pools) which have mixing of swimmers
are frequently observed (75% of the pools). This
could result to higher possibility of contamination in
either pool as it could accommodate more
swimmers in any given scenario. The prevalence of
Giardia, in both public and private pools, was higher
in adult pools than in children’s pools and may
similarly be attributed to the same rationale. This
fact could be supported by the study of Shields et al.
(2008) where they observed that pools frequented by
both adults and children showed higher parasites
prevalence compared to pools which restricted to
adult swimmers from children swimmers.
Physico-Chemical Parameters
Analysis of the physico-chemical parameters (pH,
temperature, DO and conductivity) with the pres-
ence of Giardia cysts and Cryptosporidium oocysts
showed that all the parameters have weak to mod-
erate effect on the densities of the two parasites.
Further analysis using regression coefficient simi-
larly showed that no significant relationship exists
between the physico-chemical parameters and the
densities of Giardia and Cryptosporidium
(Table 2).
Mean pH levels were shown to be largely neutral
to low basic, conditions which are not ideal to inac-
tivate both Cryptosporidium oocyst and Giardia cyst.
While the chlorination levels were not measured, the
low pH levels obtained may be indicative that the
majority of the pool waters were treated with low
concentrations of the chemical. Both parasites are
Fig. 2. Mean density (A) and prevalence (B) of
Cryptosporidium spp. and Giardia spp. in 12 swim-
ming pool samples collected from Pansol,
Calamba, Laguna.
While these findings differ from previous studies
(Hsu et al., 1999; Castro_hermina et al., 2010) in that
Giardia cysts often outnumbers Cryptosporidium
oocysts in a given sample, the study by Shields et al.
(2008) corroborates the results of the present study.
Similarly, they found high prevalence and densities
of both Cryptosporidium and Giardia in children’s
pools (92.3%) than in adult pools (7.7%). Statistical
analysis, however, were not significant between the
prevalence of the two parasite species. The higher
prevalence and densities of both parasites in
children’s pools may be attributed to incontinence
and the greater likelihood of children below 18 years
PALLER ET AL 1949
highly resistant to low levels of alkalinity and basic-
ity and requires hyperalakaline (or hyper chlori-
nated) waters to become deactivated (Current and
Navin, 1986; Jarroll, Bingham and Meyer, 1981).
Thus, little to weak strength may be attributed to the
effect of pH on the density of oocysts and cysts de-
tected and no significant relationship may be de-
duced from the two.
Although some studies show significance be-
tween temperature and densities (Olson et al., 1999;
Paller, Salumbre and de la Cruz, 2013), a high tem-
perature gradient is the constant factor for the deac-
tivation of both Cryptosporidium and Giardia (Gómez
et al., 2011; Schaefer, Rice and Hoff, 1984). Mean
temperatures of the pools were found to have a
moderate negative correlative effect, though not sta-
tistically significant. Nevertheless, it could be im-
plied that as the temperature increases there is a
slight corresponding decrease in parasite density.
The density of Giardia cysts per liter show a weak
positive correlation to dissolved oxygen while
Cryptosporidium oocyst density shows a low signifi-
cant relationship. While literature shows little to no
relationship between Cryptosporidium and dissolved
oxygen, Giardia manifests low but positive correla-
tion (Lloyd et al., 2000). Giardia is an aero-tolerant
anaerobe which can adapt to oxygenated environ-
ments outside of its host (Marr and Mueller, 1995;
Paget, Manning and Jarrol, 1993), showing limited
oxygen uptake during trophozoite and (to a degree)
cysts stage.
Correlation of both Cryptosporidium and Giardia
with conductivity shows low significant relation-
ships but differing strengths of correlative power.
Cryptosporidium is often present in samples that have
significantly higher conductivity and total dissolved
solids (Feng et al., 2011). Consequently, a high con-
ductivity (and a high TDS) implies the greater po-
tential for inoculating microbial and algal growth in
water. Though high oxygenation combined with
high temperature may prove to inactivate cysts and
oocysts, no statistical significance may be attributed
to the resulting densities of the two parasites when
correlated with the water conductivity of the pools.
Results on the correlation between
Cryptosporidium and Giardia densities and the vol-
ume of the pools showed that there is a weak to mild
negative trend. Furthermore, there is no significant
relationship between pool volume and parasite den-
sity.
Larger volume pools necessitate an equally large
amount of samples in order to gain a precise and
accurate assessment and detection of
Cryptosporidium and Giardia. The rationale behind
this is that, as the volume of water grows larger, the
probability of obtaining oocyst/cyst grows smaller.
To compensate, it becomes necessary to collect large
amounts of the samples. The same rationale would
explain the theoretical values of the correlation.
Larger pool volumes with minute amounts of oocyst
and cysts would require an equally large volume of
water to sample in order to obtain said amounts
(Aljanahi and Ali Khan, 2014).
Survey of Pool Factors
Since the study was conducted during the sum-
mer season, the number of swimmers was higher.
Table 2. Pearson correlation analyses (r) between the
physico-chemical parameters and the densities
of Cryptosporidium oocyst and Giardia cyst.
Physico-chemical parameters Density
Cryptosporidium Giardia
oocyst cyst
Pool Volume -0.261 -0.355
pH -0.149 -0.244
Water Temperature -0.436 -0.42
DO level 0.004 0.463
Conductivity -0.053 0.233
Table 3. Point-biserial analyses (r) between the pool fac-
tors and the number of Cryptosporidium oocyst &
Giardia cyst.
Parameters Parasite (r)
Cryptosporidium Giardia
Water Source:
Mountain 0.483 0.263
Deep Well -0.483 -0.263
Frequency of visitors per week:
21 - 35 -0.461 -0.178
36 - 50 -0.151 -0.063
>56 0.45 0.178
Mixed swimming between pools 0.483 0.263
(adult and children)?
Mandatory use of shower before 0.316 0.003
swimming?
Cleaning Method
Detergent 0.316 0.003
Chemical 0.166 -0.246
Frequency of cleaning pool water
Immediately after use -0.593 -0.139
Follows a schedule 0.74 0.364
Continuous water flow -0.261 -0.282
1950 Eco. Env. & Cons. 23 (4) : 2017
Though no comparison performed between the
peak and non-peak seasons, it could be predicted
that the high number of swimmers, during the peak
season, could be related to the number of the para-
sites’ densities.
It was similarly observed among selected pools
that only 25% were cleaned immediately after use,
25% had continuous water flow and 50% followed a
cleaning schedule (varying from 2 days to > 1 week).
Furthermore, during cleaning, scrubbing with the
aid of detergent (100%) and chlorine (87.5%) were
used in majority of the pools. None of the pools
were found to use any type of filter to clean the wa-
ter. Pools with continuous water flow (25%) were
only routinely vacuumed at the bottom, likely de-
limiting the removal of cysts and oocysts which
have not settled to the bottom of the pool (Solo-
Gabriele et al., 1998). Chlorine as a disinfectant may
prove less effective in eradicating both
Cryptosporidium oocysts and Giardia cysts (Gómez et
al., 2011) particularly in low concentrations.
All of the pools (100%) were relatively open with
low fencing were observed to be frequented by ani-
mals like cats and birds. Moreover, some respon-
dents added that pet dogs were sometimes carried
by their owners to the pools. These could maximize
the probability of contamination as these animals
could be reservoir hosts and may transmit the para-
sites zoonotically (Dixon et al., 2011).
Analysis using point-biserial correlation shows
no significant relationship between parasite densi-
ties and the survey parameters (Table 3), which
could be attributed to the low sampling size. How-
ever, commonalities may be observed from the
qualitative interpretations of the survey. Among the
frequently cited factors which imply an effect to the
density and prevalence of the parasites are the prac-
tice of mixed bathing between adult and children’s
pool and the lax regulation of this practice. The
study by Shields et al. (2008) concurs higher detec-
tion of the two water-borne protozoans in mixed
pools rather than from adult or children’s pools
alone. It is likely that increased detection is related
to the high number of individuals which can poten-
tially harbor the parasite.
Conclusion
This research is a baseline study for protozoan para-
site contamination in recreational pools in the coun-
try. Few studies in the Philippines have addressed
the presence of protozoan parasites in recreational
pools particularly in frequently visited tourist areas.
The present study showed a high percent of con-
tamination in a number of public and private pools.
It also established a greater degree of contamination
in children’s pool compared to adults. Survey of
pool practices similarly allowed for establishment of
some factors which affected the contamination and
transmission of the Cryptosporidium oocysts and
Giardia cyst.
The absence of conventional backwash and sand
filters in all of the local pool facilities prevented the
collection of smaller concentrated samples and in-
stead necessitated on direct sampling of large vol-
umes of pool water. Comparison of the study with
other research which used serial or backwash
samples as well as on studies which focused on a
large sampling size of pools may prove difficult.
However, a key aspect of the study focuses on the
presence of Cryptosporidium sp. and Giardia sp. in
some swimming pools and emphasizes the necessity
of improvements of pool operation and mainte-
nance. The results highlight the need for pool own-
ers, caretakers and bathers to understand the health-
hazards posed by water-borne parasites and act to
adapt the necessary measures to reduce the risk of
transmission. Thus, the study suggests the formation
of policy brief to address the potential risks of the
parasites and suggest the ideal protocol which will
minimize the outbreak in both public and private
pools.
Acknowledgement
The authors are thankful to the pool operators and
owners who participated in this study. We are also
grateful to the Environmental Biology Division of
University of the Philippines Los Baños for the use
of the measuring instruments/meters, and to Ms.
Rowena Oane for her supervision of using the
epiflourescent microscope.
References
Aljanahi, A. A. A. and Khan, M.A. 2014. A Preliminary
Assessment of the Occurrence of Cryptosporidium
and Giardia in the School Swimming Pool Water in
Dubai, United Arab Emirates. International Journal of
Environmental Science and Development. 5(3): 303.
DOI: 10.7763/IJESD. 2014.V5.497.
ALS Environmental Limited. 21 May 2014. Analysis of
Cryptosporidium and Giardia in water. Retrieved from
<http://www.alsenvironmental.co.uk/media-uk/pdf/
datasheets/drinkingwater/als_dw_crypto_v1_2014.pdf>
City Government of Calamba. 2015. Brgy. Pansol. Re-
PALLER ET AL 1951
trieved from <http://www.calambacity.gov.ph/
index.php/11-government/82-barangay-pansol/>.
Carey, C. M., Lee, H. and Trevors, J. T. 2004. Biology, per-
sistence and detection of Cryptosporidium parvum
and Cryptosporidium hominis oocyst. Water research,
38(4): 818-862. DOI:10.1016/j.watres.2003.10.012.
Castro-Hermida, J.A. Garcia-Presedo, I., lez-Warleta, M.G
and Mezo, M. 2010. Cryptosporidium and Giardia
detection in water bodies of Galazia, Spain. Water
Research. 44: 5887-5896. DOI: 10.1016/
j.watres.2010.07.010
CDC. 1 April 2015a. Cryptosporidiosis: Sources of Infec-
tion and Risk Factors. Retrieved from <http://
www.cdc.gov/parasites/crypto/infection-
sources.html>.
CDC. 21 July 2015b. Giardiasis: Sources of Infection and
Risk Factors. Retrieved from <http://www.cdc.gov/
parasites/Giardia/infection-sources.html>.
Current, W.L. and Navin, T.R. 1986. Cryptosporidium: its
biology and potential for environmental transmis-
sion. Critical Reviews in Environmental Science and
Technology. 17 (1): 21-51. DOI: 10.1080/
10643388609388328.
Dixon, B. R., Fayer, R., Santin, M., Hill, D. E., Dubey, J. P.,
and Hoorfar, J. 2011. Protozoan parasites:
Cryptosporidium, Giardia, Cyclospora, and Toxoplasma.
Pp. 349-370. Rapid detection, characterization, and enu-
meration of foodborne pathogens. APMIS.
Fayer, R., Morgan, U. and Upton, S. J. 2000. Epidemiology
of Cryptosporidium: transmission, detection and
identification. International Journal for Parasitology.
30(12): 1305-22. DOI: 10.1016/S0020-7519(00)00135-
1.
Feng, Y., Zhao, X., Chen, J., Jin, W., Zhou, X., Li, N., Wang,
L. and Xiao, L. 2011. Occurrence, source, and human
infection potential of Cryptosporidium and Giardia
spp. in source and tap water in Shanghai, China.
Applied and Environmental Microbiology. 77 (11) :
3609-16.
Gerba, C. P. 2000. Assessment of enteric pathogen shed-
ding by bathers during recreational activity and its
impact on water quality. Quantitative Microbiology.
2(1): 55-68. DOI: 10.1023/A:1010000230103.
Gómez, M. S., GraceneaZugarramurdi, M., Ángel Ripoll,
L. and Beneyto, V. 2011. Cryptosporidium sp. in pub-
lic swimming pools in Barcelona. Recent Advances in
Pharmaceutical Sciences. Chapter 12. 275-282.
Hsu, B.M, Huang, C. and Hsu, C.L. 2001. Analysis for
Giardia cyst and Cryptosporidium oocyst in water
samples from small water systems in Taiwan.
Parasitol Res. 87(2): 163-168. DOI:10.1007/
PL00008570
Jarroll, E. L., Bingham, A. K. and Meyer, E. A. 1981. Effect
of chlorine on Giardia lamblia cyst viability. Applied
and Environmental Microbiology. 41 (2) : 483-487.
Lloyd, D., Harris, J., Maroulis, S., Biagini, G., Wadley, R.,
Turner, M. and MR Edwards. 2000. The microaero-
philic flagellate Giardia intestinalis: oxygen and its
reaction products collapse membrane potential and
cause cytotoxicity. Microbiology. 3109.
Marr, J. and Muller, M. 1995. Biochemistry and Molecular
Biology of Parasites. Academic Press Limited. Lon-
don. 20-23.
Natividad, F.F., Buerano, C.C., Lago, C.B., Mapua, C.A.,
de Guzman, B.B., Seraspe, E.B., Samentar, L.P. and
Endo, T. 2008. Prevalence rates of Giardia and
Cryptosporidium among diarrheic patients in the
Philippines. Southeast Asian J Trop Med Public Health,
39(6): 991-9.
Olson, M. E., Goh, J., Phillips, M., Guselle, N. and
McAllister, T. A. 1999. Giardia cyst and Cryptos-
poridium oocyst survival in water, soil, and cattle
feces. Journal of Environmental Quality. 28 (6) : 1991-
96. DOI: 10.2134/jeq1999.00472425002800060040x.
Onichandran, S., Kumar, T., Salibay, C.C., Dungca, J.Z.,
Tabo, H.A., Tabo, N., Tan, T.C., Lim, Y.A.,
Sawangjaroen, N., Phiriyasamith, S. and
Andiappan, H. 2014. Waterborne parasites: a cur-
rent status from the Philippines. Parasit Vectors. 7(1):
244. DOI: 10.1186/1756-3305-7-244.
Paget, T., Manning, P. and Jarroll. E. 1993. Oxygen Uptake
in Cysts and Trophozoites of Giardia lamblia. J. Euk.
Microbiology. 246-250. DOI: 10.1111/j.1550-7408.
1993.tb04911.
Paller, V. G. V., Salumbre, R. L. and de la Cruz, C. P. P.
2013. Asian clams (Corbicula fluminea) as
bioindicators of Cryptosporidium contamination in
Laguna de Bay, Philippines. Ecology, Environment
and Conservation. 19 (3) : 635-642.
Rivera, W. L. and Yason, J. A. D. 2009. Molecular detection
of Cryptosporidium from animal hosts in the Philip-
pines. The Philippine Agricultural Scientist. 91: 473-
477.
Schaefer, F. W., Rice, E. W. and Hoff, J. C. 1984. Factors
promoting in vitro excystation of Giardia muris cysts.
Transactions of the Royal Society of Tropical Medicine
and Hygiene. 78(6): 795-800. DOI: 10.1016/0035-
9203(84)90024-5.
Shields, J. M., Gleim, E. R. and Beach, M. J. 2008. Preva-
lence of Cryptosporidium spp. and Giardia intestinalis
in swimming pools, Atlanta, Georgia. Emerg Infect
Dis. 14(6): 948-950. DOI: 10.3201/eid1406.071495.
Solo-Gabriele, H. M., Ager Jr, A. L., Lindo, J. F., Dubón, J.
M., Neumeister, S. M., Baum, M. K. and Palmer, C.
J. 1998. Occurrence of Cryptosporidium oocysts and
Giardia cysts in water supplies of San Pedro Sula,
Honduras. Revista Panamerica de SaludPública. 4: 398–
400. DOI: 10.1590/S1020-49891998001200006.
The Environmental Protection Agency. 26 September
2011. EPA drinking water advice note no. 9:
Cryptosporidium sampling and monitoring version 1.
Retrieved from <https://www.epa.gov/sites/pro-
duction/files/2015-10/documents/
Cryptosporidium-report.pdf>.
