Infection rate of Schistosoma japonicum in the snail Oncomelania hupensis quadrasi in endemic villages in the Philippines: Need for snail surveillance technique

Abstract

Schistosomiasis japonica is one of seven NTDs endemic in the Philippines that
continues to threaten public health in the country. The causative agent, the blood fluke
Schistosoma japonicum, uses an amphibious snail Oncomelania hupensis quadrasi which
can harbor larval stages that multiply asexually, eventually producing the infective cercariae which are shed into the water. Contamination of freshwater bodies inhabited by the snail intermediate host occurs through release of human and animal feces containing S. japonicum eggs. Miracidia hatching from these eggs subsequently infect the snails that
inhabit these water bodies. The degree of fecal contamination can vary across snail sites
and influences snail infection rates in these sites. In this study, conventional malacological
surveys using intensive manual search for snails were conducted from 2015 to 2016 in
seven selected endemic provinces, namely Leyte and Bohol in the Visayas and Surigao del
Norte, Agusan del Sur, Bukidnon, Lanao del Norte and Compostela Valley in Mindanao. A
total of 6,279 O. hupensis quadrasi snails were collected from 38 snail sites. The
municipality of Trento in Agusan del Sur recorded the highest number of snail sites (7) that yielded O. hupensis quadrasi snails while only one snail site was found positive for O.
hupensis quadrasi snails in Kapatagan in Lanao del Norte and Talibon in Bohol. Alegria in
Surigao del Norte yielded the highest number of snail sites (5) that were found to harbor
snails positive for S. japonicum infection. The snail infection rates in this municipality
ranged from 0.43% to 14.71%. None of the snails collected from Talibon in Bohol was
infected. Bohol is the only province among the 28 schistosomiasis-endemic provinces
which has reached near elimination status. Snail infection rates were found to vary
considerably across snail sites, which could be due to the degree of fecal contamination of the snail sites and their connectivity to water that can serve as contamination source.

Full text

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Tropical Biomedicine 36(2): 402–411 (2019)
Infection rate of Schistosoma japonicum in the snail
Oncomelania hupensis quadrasi in endemic villages in
the Philippines: Need for snail surveillance technique
Fornillos, R.J.C.1*, Fontanilla, I.K.C.1, Chigusa, Y.2, Kikuchi, M.3, Kirinoki, M.2, Kato-Hayashi, N.2,
Kawazu, S.4, Angeles, J.M.4, Tabios, I.K.5, Moendeg, K.4,6, Goto, Y.7, Tamayo, P.G.8, Gampoy, E.F.5,
Pates, I.8, Chua, J.C.9 and Leonardo, L.R.1,8
1Institute of Biology, National Science Complex, College of Science, University of the Philippines Diliman,
Regidor St, Quezon City, 1101 Metro Manila, Philippines
2Department of Tropical Medicine and Parasitology, Dokkyo Medical University, 880 Kitakobayashi,
Mibu-machi, Shimotsuga-gun, Tochigi, Japan
3Department of Immunogenetics, Institute of Tropical Medicine (NEKKEN) Nagasaki University, Nagasaki,
Japan
4National Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine,
Obihiro, Hokkaido, Japan
5College of Medicine, University of the Philippines Manila, 625 Pedro Gil St, Ermita, 1000 Metro Manila,
Philippines
6Department of Biology, School of Science and Engineering, Ateneo de Manila University, Loyola Heights,
Quezon City 1108, Metro Manila, Philippines
7Graduate School Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan
8Department of Parasitology, College of Public Health, University of the Philippines Manila,
625 Pedro Gil St, Ermita, 1000 Metro Manila Manila
9College of Medical Technology, Chinese General Hospital, 286 Blumentritt St, Sta. Cruz,
1014 Metro Manila, Philippines
*Corresponding author e-mail: raffyjayfornillos@gmail.com
Received 2 July 2018; received in revised form 31 December 2018; accepted 2 February 2019
Abstract. Schistosomiasis japonica is one of seven NTDs endemic in the Philippines that
continues to threaten public health in the country. The causative agent, the blood fluke
Schistosoma japonicum, uses an amphibious snail Oncomelania hupensis quadrasi which
can harbor larval stages that multiply asexually, eventually producing the infective cercariae
which are shed into the water. Contamination of freshwater bodies inhabited by the snail
intermediate host occurs through release of human and animal feces containing S.
japonicum eggs. Miracidia hatching from these eggs subsequently infect the snails that
inhabit these water bodies. The degree of fecal contamination can vary across snail sites
and influences snail infection rates in these sites. In this study, conventional malacological
surveys using intensive manual search for snails were conducted from 2015 to 2016 in
seven selected endemic provinces, namely Leyte and Bohol in the Visayas and Surigao del
Norte, Agusan del Sur, Bukidnon, Lanao del Norte and Compostela Valley in Mindanao. A
total of 6,279 O. hupensis quadrasi snails were collected from 38 snail sites. The
municipality of Trento in Agusan del Sur recorded the highest number of snail sites (7) that
yielded O. hupensis quadrasi snails while only one snail site was found positive for O.
hupensis quadrasi snails in Kapatagan in Lanao del Norte and Talibon in Bohol. Alegria in
Surigao del Norte yielded the highest number of snail sites (5) that were found to harbor
snails positive for S. japonicum infection. The snail infection rates in this municipality
ranged from 0.43% to 14.71%. None of the snails collected from Talibon in Bohol was
infected. Bohol is the only province among the 28 schistosomiasis-endemic provinces
which has reached near elimination status. Snail infection rates were found to vary
considerably across snail sites, which could be due to the degree of fecal contamination of
the snail sites and their connectivity to water that can serve as contamination source.

403
INTRODUCTION
Schistosomiasis japonica which was
discovered in the Philippines in 1906
continues to threaten the health of
agricultural communities especially the
farmers, fishermen and children who remain
constantly exposed to the disease through
their work and habits (Blas et al., 2004).
The disease is endemic in 12 regions of
the country covering 28 provinces, 14
cities, 189 municipalities and 2,221
barangays (Leonardo et al., 2016). O.
hupensis quadrasi was first described by
Mollendörff from specimens collected in
Surigao (McMullen et al., 1947) (Figure 1).
In 1932, Dr. Marcos Tubangui confirmed
the epidemiological role of O. hupensis
quadrasi as intermediate host to S.
japonicum from samples collected at
Barrio Gacao, Palo, Leyte (Blas 1988-89;
Leonardo et al., 2016).
To date, approximately 12 million
Filipinos are living in endemic areas, and
2.5 million individuals are directly exposed
to infection (Blas et al., 2004; Leonardo et
al., 2012, 2015, 2016). O. hupensis quadrasi
thrives in a wide array of freshwater bodies
such as rice fields, cemented waterways,
canals, irrigation systems, swamps,
lakeshores, riverbanks, and other shaded
and waterlogged areas (Blas, 1988-89;
Tanaka et al., 1978; Ohmae et al., 2003).
Some snail sites are located in close
proximity to households in endemic areas.
Since snail colonies populate rice fields
or irrigation canals, S. japonicum is
considered an occupational hazard among
farmers and inland fishermen (Blas,
1988-89).
Poor sanitation practices in endemic
areas perpetuate environmental con-
tamination with schistosome eggs while
lack of access to clean water increases risk
of exposure to the disease when people go
to possibly contaminated water bodies to
launder their clothes, wash their dishes
and bathe (Blas, 1991). A human infection
survey by Leonardo et al. (2008) in 13
provinces in Mindanao and five provinces
in the Visayas reported a prevalence rate
ranging from 0.08% (Agusan del Norte) to
3.95% (Agusan del Sur). New endemic foci
for schistosomiasis were further discovered
in Gonzaga, Cagayan Valley and Calatrava,
Negros Occidental in 2002 and 2005,
respectively. Various diagnostic procedures
from stool examination (Kato-Katz),
serodiagnosis (COPT and ELISA), and
ultrasound were used to confirm cases of
schistosomiasis in these new foci (Leonardo
et al., 2015). Based from the report of the
Philippine Department of Health in 2018,
1611 villages (barangays) are still endemic
to schistosomiasis with around 188 are
low endemic (11.67%), 382 are moderately
endemic, and 453 are highly endemic
(28.12%). For zero prevalence barangays,
242 (15.02%) have been recorded, but 346
remain to be determined due to lack of focal
surveys done in these areas. Stratification
of endemicity of villages were based on the
prevalence recorded during focal surveys
with >5% in high endemic areas, >1% but
<5% in moderately endemic and <1% in low
endemic areas (DOH, 2018).
A multifaceted schistosomiasis program
is required for the successful control and
eventual elimination of the disease, and
this necessitates sustained and regular data
from human, animal, and snail surveys.
Malacological surveys yield data such as
snail density, distribution and infection rate,
which can be used as indicators of the
possible extent of distribution and rate of
transmission of the disease (UP CPH
Foundation, 2012). This study therefore
aimed to provide baseline data of the snail
infection rate in seven selected endemic
Figure 1. Oncomelania hupensis quadrasi
(Mollendörff, 1895) snail collected from Alegria,
Surigao del Norte, Philippines.

404
provinces and provide information for
potential areas for transmission.
MATERIALS AND METHODS
Malacological surveys were conducted in
seven municipalities representing seven
schistosomiasis-endemic provinces that
were selected based on the national
prevalence survey conducted in 2005-
2008 (Leonardo et al., 2008, 2012). These
provinces were Bohol and Leyte in the
Visayas and Surigao del Norte, Agusan del
Sur, Bukidnon, Lanao del Norte, and
Compostela Valley in Mindanao (Table 1,
Figure 2A). Surveys were done from April
2015 to January 2016 (Table 1) through
intensive and purposive search in sites
known to support O. hupensis quadrasi
snails. There were common ecological
characteristics in the snail sites visited,
which include being waterlogged and
with thick vegetation shading swamps,
riverbanks, rice fields, irrigation canals,
ponds, and streams (Figure 2B-E). Survey
was done for one day from 8 am to 12 noon
and 1 pm to 3 pm. The number of snail
collectors per site varied depending on the
availability of personnel at the time of
survey (Table 1). The snails were collected
using forceps and placed in properly labeled
containers, after which they were air
dried in a conventional filter paper away
from direct exposure to sunlight or heat. Air
dried snails were transferred and packed
carefully in clean sheets of filter paper
and transported to the Department of
Parasitology, University of the Philippines
Manila for further processing.
Identity of snails was confirmed by
examination of shell morphology. O.
hupensis quadrasi snails have a distinct
ovately conic shell shape with sharp apex.
Shell color may vary from brown to black.
Juvenile snails are 3 milimeters (mm) in
Table 1. List of selected barangays surveyed in municipalities across seven provinces endemic to
schistosomiasis japonica in the Philippines
Endemic Villages/ Date No. of No. of
Island Province Municipality/ Barangays Surveyed Collectors sites
City surveyed
Leyte Northern Alang-alang Bugho, San Apr 13-17, 5 8
Leyte Antonio Farm, 2015
San Vicente
Bohol Bohol Talibon San Roque Jul 28-31, 4 1
2015
Agusan del Trento Manat, Jul 13-17, 5 11
Sur Tudela, 2015
San Isidro
Surigao del Alegria Poblacion, Aug 4-7, 5 8
Norte Alipao, 2015
San Pedro
Mindanao Lanao del Kapatagan Bagong Oct 27-30, 4 3
Norte Silang 2015
Curvada,
De Asis
Bukidnon Valencia Kahaponan, Nov 30- 3 3
Vintar, Dec 4,
San Isidro 2015
Compostela Maragusan Tigbao, Jan 24-27, 6 4
Valley Mapawa, 2016
New Albay

405
Figure 2. (A) Seven provinces in the Philippines surveyed for S. japonicum
infection to O. hupensis quadrasi snails. Visayas: Leyte, Bohol; Mindanao: Surigao
del Norte, Agusan del Sur, Bukidnon, Lanao del Norte, Compostela Valley. (B)
Malacological survey conducted in a rice field in Trento, Agusan del Sur with O.
h. quadrasi snails, (C) Sarong boggy, a snail site in a swampy area in Talibon,
Bohol, (D) wide and deep irrigation canals supplying water in many rice fields in
Agusan del Sur, (E) an O. hupensis quadrasi attached to a stone collected from a
riverside in Valencia, Bukidnon.
length or less and adult snails are 3 mm with
maximum of 6 mm in length (Garcia, 1988;
Leonardo & Solon, 1996).
Snail infection was determined micro-
scopically by demonstrating schistosome
cercariae and sporocysts in crushed snails.
Snails were placed individually in three
drops of distilled water in a glass slide. The
snails were crushed by pressing another
clean slide on top of the slide with the snails.
Snail tissues were further teased and shell
debris removed to better expose the
schistosome cercariae and sporocysts. The
crushed snails were examined under a

406
stereomicroscope (Bausch & Lomb OPT. Co.
U.S.A.). Snails were considered infected if
the characteristic furcocercous cercariae
and sac-like sporocysts were seen. The rate
of infection for the municipality surveyed
was computed as follows: [(number of
infected snails)/ (total number of collected
snails examined)] x100.
RESULTS
A total of 6,279 O. hupensis quadrasi
snails were collected from the seven
municipalities (Table 2). Agusan del Sur
yielded the highest number of sites surveyed
at 11 sites while the least number was in
Talibon, Bohol with only one site (Tables 1
& 2). The highest number of collected snails
was recorded in Agusan del Sur with a total
of 1,683 snails from Barangays Manat,
Tudela, and San Isidro (Table 2). The least
number was recorded in Valencia, Bukidnon
with 133 snails from Barangays Vintar,
Kahaponan, and San Isidro (Table 2). It was
observed during the survey that not much
is known about snail sites in Valencia,
Bukidnon. In the light of this paucity of
information, the survey was extended to all
possible snail habitats such as tributaries
of rivers, rice fields and water-logged areas,
which revealed few interspersed clumps of
snails. In Agusan del Sur where prevalence
of the disease has been known to be high,
sanitary inspectors and malacologists
previously conducted malacological
surveys to monitor the snail intermediate
hosts. Thus, records of snail sites and
their location provided crucial a priori
information on the municipality, leading to
a more focused survey and subsequently
resulting to a very high number of collected
snails.
The highest number of snail sites with
infected snails was recorded in Alegria,
Surigao del Norte (SDN) with five sites
(Table 1, Figure 3). Table 2 shows that snails
positive for schistosome infection were
found in snail sites surveyed in the 6 of the
7 provinces covered. The snails found from
the single site in Talibon, Bohol were
negative for S. japonicum cercariae or
sporocysts, the only province in this study
to yield such result (Tables 2 & 3). It should
be noted that among the 28 provinces which
are presently endemic for schistosomiasis,
only Bohol has reached near elimination
status on the basis of the absence of human
cases for the past many years according to
health authorities (Leonardo personal
communication). Widest range of snail
infection rate (IR) was noted in Alegria,
Surigao del Norte (0.43%–14.71%) while the
narrowest IR range was recorded in
Valencia, Bukidnon (0%-1.72%) (Table 3).
DISCUSSION
In the Philippines, the cornerstone of
schistosomiasis control has been mass drug
administration (MDA) while snail control
has not been given that much attention.
Malacological surveys are not regularly
Table 2. Summary of results for the different municipalities based on the malacological surveys conducted
from April 2015 to January 2016
Municipality Sites with Sites with Number of Number of
Ohq infected Ohq (%) collected snails infected snails (%)
Talibon 1 0 (0.00) 38 8 0 (0.00)
Alang-alang 5 3 (60.0) 1588 9 (0.57)
Trento 7 3 (42.9) 1683 6 (0.36)
Alegria 6 5 (83.3) 1229 12 (0.98)
Kapatagan 1 1 (100.0) 461 4 (0.87)
Valencia 3 1 (33.3) 1 33 1 (0.75)
Maragusan 4 3 (75.0) 7 97 12 (1.51)
Note: Ohq = Oncomelania hupensis quadrasi.

407
Table 3. Summary of snail infection rates (IR) of snail sites from the endemic municipalities
Island Province Municipality Site IR (%)
Maragusan 1 0
Compostela Valley Maragusan Maragusan 2 1.89
Maragusan 3 1.03
Maragusan 4 2.15
SDN 1 14.71
SDN 2 0.65
Surigao del Norte Alegria SDN 3 1.19
SDN 4 0.43
SDN 5 0.65
Mindanao
BKN 1 1.72
Bukidnon Valencia BKN 2 0
BKN 3 0
Agusan 1 0
Agusan 2 0
Agusan 3 2.22
Agusan del Norte Trento Agusan 4 0.32
Agusan 5 0
Agusan 6 2.38
Agusan 7 0
Bohol Bohol Talibon Bohol 0
Leyte 1 1
Leyte Leyte Alang-alang Leyte 2 0
Leyte 3 0.36
Leyte 4 0
conducted so that snail sites are not updated
and transmission sites are not identified.
The situation in Valencia, Bukidnon
illustrates this problem clearly where
paucity of information is further perpetuated
by the lack of manpower to conduct snail
surveys. In contrast, control efforts in
Agusan del Sur have included snails to bring
down the consistently high prevalence of
schistosomiasis in the province. While the
data for Bohol may be promising, i.e. no
infected snails and human cases, further
surveillance using more sensitive serologic
tests on humans and other animal reservoir
hosts and regular snail surveys should be
conducted to confirm the near elimination
status of schistosomiasis in the province and
potentially towards full elimination status.
In China, infected snails were still observed
even in areas where transmission was
declared to be controlled. Few areas showed
a decreasing trend in snail infection rate
while other areas that were monitored
for snail surveillance worsened, indicating
that snail control should be focused and
reinforced most especially in areas where
transmission were under control (Gen-Ming
et al., 2005).
In Alegria, Surigao del Norte, one snail
site (SDN1) was observed to have the highest
infection with 14.71% (Table 3). This snail
site was observed to be near human
settlement and even a pig farm and was
therefore a recipient of domestic wastes.

408
High snail infection rates are indicative of
intense fecal contamination either from
infected humans or infected animals caused
by poor environmental sanitation or failure
to manage waste disposal from livestock.
While snail population density and snail
distribution are important indicators of
possible presence and spatial distribution
of schistosomiasis, a better parameter
that indicates disease transmission is
snail infection rate. The lone snail site in
Kapatagan, Lanao del Norte (1/1 = 100%)
was found to harbor infected snails
(Table 2). This result should be a red flag
for the municipality, and efforts should be
intensified to locate more snail sites and
examine these for the presence of snails and
determine if they are infected. The presence
of infected snails means that their habitat is
being contaminated with feces coming
from infected vertebrates. Unless access
by potential hosts are restricted or removed
to disrupt the life cycle of the parasite,
this site will remain a transmission site.
Moreover, snail infection rate can be an
ideal monitoring tool to assess progress in
intervention programs such as MDA and
environmental sanitation. If these two main
key strategies are neglected and efforts not
sustained, infected cases without access to
clean and safe water for domestic purposes
will certainly contaminate freshwater bodies
where O. hupensis quadrasi colonies
thrive, infecting these snails.
Previous studies reporting snail
infection rates were conducted in other
endemic areas in the Philippines such as
Gonzaga in Cagayan Valley, Calatrava in
Negros Occidental, and Samar (Madsen
et al., 2008; Leonardo et al., 2015). For
instance, Leonardo et al. (2015) noted
higher snail infection rates in Gonzaga than
in Calatrava, particularly in Barangay
Magrafil that can be attributed to the closer
proximity of snails to human habitation
and the presence of infected animals that
may continuously contaminate the water
and subsequently infect the snails. Other
barangays showed comparatively lower
snail infection rates, and variability of snail
infection rates across barangays was high.
In another study, Madsen et al. (2008) com-
pared naturally rain-fed and artificially
irrigated villages and noted no significant
difference in snail density but with signifi-
cantly higher infection rate in artificially
irrigated villages, which they attributed to
the steady and consistent supply of water in
these areas that allowed for longer stay of
snail colonies and therefore greater
exposure time to the parasites.
The current study shows the importance
of snail data in elucidating the status of
schistosomiasis in endemic areas. Snail
population density, spatial distribution and
snail infection rates are critical indicators
of the possible presence and distribution
of the disease as well as occurrence of
transmission. The number of snails collected
and snail infection rate vary even if the snail
sites demonstrate striking similarity in
ecological characteristics such as being
waterlogged with thick vegetation. There-
fore, snail surveys must be regularly
conducted in schistosomiasis endemic
provinces.
The importance of identifying sites
positive not only for snails but for snails
infected with S. japonicum could not be
overemphasized. Whilst municipalities like
Talibon, Kapatagan and Valencia have only
few snail sites or sites with infected snails,
this information should spur them to
intensify efforts in expanding their surveys
to include other unvisited sites to determine
potential transmission sites.
For other endemic municipalities
such as Alang-alang, Trento, Alegria and
Maragusan, having identified the snail sites
and those with infected snails puts them at
first base, but further steps should be
undertaken such as restricting access of
humans and domesticated animals to these
sites in order to disrupt the life cycle of
S. japonicum.
Identification and mapping of snail
sites and continuous monitoring for snail
infection are therefore important com-
ponents of snail surveillance, which should
be standard for schistosomiasis intervention
programs in endemic areas. Snail control
methods can be done through environmental
modification measures such as cement
lining, dredging, and burying in order to

409
destroy the snail habitats. Japan was able
to eliminate schistosomiasis in the 1990’s
using mostly by mostly transforming
waterlogged areas into fruit plantations,
burying snail habitats, and converting them
into residences and even golf courses. To
date, however, O. hupensis nosophora, the
snail intermediate host of schistosomiasis
in Japan, remains in large number in
previously endemic areas in Japan such
as Yamanashi-Kofu River Basin, though no
human and animal cases have been noted
since 1977 after continuous control efforts
(Tanaka & Tsuji, 1997). This just goes to
show that the disease can be eliminated
without eliminating the snail intermediate
host. What is essential is to prevent trans-
mission by keeping the snails free from S.
japonicum infection.
In light of the call for elimination of
schistosomiasis by 2030, endemic countries
are encouraged to intensify control and
elimination efforts starting with deve-
lopment not only of highly sensitive
diagnostic methods to detect the disease in
humans and animal reservoirs but identify
snail sites and determine snail infection
rate. The Philippines can place its hopes on
Bohol to be the first province to eliminate
schistosomiasis given its present status of
no infected snails and no infected humans
(using Kato-Katz for diagnosis).
However, 0% infection rate status
must be confidently ascertained through
extensive snail survey coupled with the use
of sensitive diagnostic tools. Malacological
surveys could be very laborious, time-
consuming, and unreliable especially since
many of those involved may not have the
necessary expertise in identifying snails let
alone determine snail infection rate. Another
downside of intensive manual search is the
physical hazard in accessing possible snail
sites that can only be reached after crossing
steep and slippery slopes or boggy marsh
with unstable substrate.
A possible complement currently being
explored is detection of environmental
DNA (eDNA) from the parasite or the snail
intermediate host. This provides a rapid
and more accurate method that is also
safer to use. Several molecular markers
have already been used in detecting
helminth parasites. These markers include
transposons and retrotransposons for S.
japonicum (Driscoll et al., 2005; Hung &
Remais, 2008), and cytochrome c oxidase
subunit 1 gene (cox1) for O. viverrini
and O. lobatus (Hashizume et al., 2017).
Presence of environmental DNA (eDNA)
is indicative of the target organism’s
presence and can be used to estimate range
of endemicity of the parasite in a sampled
area.
CONCLUSION
Malacological surveys using intensive
search were used to confirm the presence
of snails in previously located snail sites
in selected villages in endemic muni-
cipalities in seven schistosomiasis endemic
provinces. The extent of collection in terms
of how many snail sites surveyed and the
number of snails collected was influenced
by available information on these snail
sites. Snail infection rates varied across
snail sites even if conditions seem to be
similar like heavily shaded water logged
areas. Variation was attributed to degree of
fecal contamination of the sites and/or their
degree of connectivity to sources of fecal
contamination.
RECOMMENDATIONS
The present conventional malacological
surveys through intensive search can yield
fruitful results if there is enough manpower
and enough expertise in identifying snails
and the infective cercariae and sporocysts.
In the light of intensifying surveillance to
support efforts for elimination of the disease,
an alternative technique through eDNA
detection in water samples collected from
existing snail sites and possible snail sites
can be explored.
Acknowledgements. We thank the Depart-
ment of Science and Technology-Philippine
Council for Health Research and Deve-
lopment (DOST-PCHRD) and Accelerated

410
Science and Technology Human Resources
Development Program, DOST Science
Education Institute (ASTHRDP-DOST-SEI)
for funding this study. We also acknowledge
Nagasaki University, Dokkyo Medical
University, University of Tokyo, Obihiro
University of Agriculture and Veterinary
Medicine, rural health units of all
schistosomiasis-endemic municipalities,
and the local sanitary inspectors and
malacologists for the logistical support.
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