247Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 101(Suppl. I): 247-251, 2006
Biomphalaria tenagophila: dynamics of populations of resistant
and susceptible strains to Schistosoma mansoni, with or without
pressure of the parasite
Florence Mara Rosa, Ana Lúcia Brunialti Godard*, Deborah Negrão-Correa,
Horácio Antonio Rodrigues*, Omar dos Santos Carvalho**, Roberta Lima Caldeira**,
Horácio Manoel Santana Teles*** Engels Maciel****, Liana Konovaloff Jannotti-Passos**,
Paulo Marcos Zech Coelho**/*****/+
Departamento de Parasitologia *Departamento de Biologia Geral, Instituto de Ciências Biológicas, UFMG, Belo Horizonte, MG,
Brasil **Centro de Pesquisas René-Rachou-Fiocruz, Av. Augusto de Lima 1715, 30190-002 Belo Horizonte, MG, Brasil
***Superintendência de Controle de Endemias do Estado de São Paulo, São Paulo, SP, Brasil ****Chácara Santa Inês, Bananal,
SP, Brasil *****Santa Casa de Misericórdia de Belo Horizonte, Belo Horizonte, MG, Brasil
Resistant (Taim, RS) and susceptible albino (Joinville, SC) Biomphalaria tenagophila populations were kept
together, at different proportions, throughout a 18-month-period. Some of the snail groups were submitted to
Schistosoma mansoni infection. The targets of this study were (a) to analyze the populational dynamics among
resistant and susceptible individuals to S. mansoni; (b) to study the resistance phenotype in descendants of cross-
breeding; (c) to observe whether the parasite could exert any kind of selection in those snail populations. Through-
out the experiment it could be observed that the susceptible B. tenagophila strain (Joinville) underwent a selective
pressure of the parasite that was negative, since the individuals showed a high mortality rate. Although B. tenagophila
(Taim) population presented a higher mortality rate without pressure of the parasite, this event was compensated by
a reproductive capacity. B. tenagophila Taim was more fecund than B. tenagophila Joinville and was able to transmit
the resistance character to their descendants. F1 generation obtained by cross-breeding between resistant and
susceptible lineages was completely resistant to S. mansoni infection, irrespective of the Taim proportion. Moreover,
less than 5% of F2 progeny were susceptible to S. mansoni infection.
Key words: Biomphalaria tenagophila - dynamics of populations - Schistosoma mansoni - resistant and susceptible strains
Distribution of Biomphalaria tenagophila snails has
considerably been spread through the Brazilian territory,
and its importance in the transmission of schistosomiasis
has been increased as well, mainly in the Southern and
Southeastern regions of Brazil (Paraense & Corrêa 1987).
This is the only transmitter species in extensive areas of
the state of São Paulo, and it is responsible for isolated
focuses in the states of Minas Gerais, Santa Catarina, and
Rio de Janeiro.
Paraense and Corrêa (1978) demonstrated that B.
tenagophila from different localities presented diversi-
fied susceptibility levels, when submitted to the SJ strain
(São José dos Campos, SP) of Schistosoma mansoni.
Santos et al. (1979) carried out a study with B. tenagophila
dealing with two interesting susceptibility profiles: a 100%
susceptible strain (Cabo Frio, RJ) and another one highly
resistant (Taim, RS). This resistant strain proceeds from
the Ecological Station at Taim, state of Rio Grande do Sul,
and has been the target of several studies. These snails,
at different ages, have continuously been resistant to
various strains of S. mansoni, as well as to different bur-
Financial support: CNPq-Fapemig-Pronex
+Corresponding author: email@example.com
Received 25 May 2006
Accepted 26 June 2006
dens of miracidia. The detected resistance was not due to
the result of a physiological incompatibility between host-
parasite, rather than to the innate defense system of the
mollusc itself (Coelho et al. 2004).
Resistance in B. tenagophila, as well as in B. glabrata,
is also associated with genetic factors. Previous studies
dealing with cross breedings between B. tenagophila from
Taim/RS and susceptible specimens of B. tenagophila
from BH/MG and Joinville/SC showed that F1 descen-
dants, as a result of such cross-breedings, presented low
suscetibility levels to S. mansoni (Santos et al. 1979, Freitas
et al. 1985). Recently, several cross-breedings were car-
ried out using a resistant strain (B. tenagophila Taim)
and a susceptible albino one (B. tenagophila Joinville).
Studying the phenotype of F1 and F2 descendants of those
cross-breedings, it was observed that the resistance char-
acter could be determined by two dominant genes, and
probably some genetic and environmental factors could
modulate this response (Rosa et al. 2005).
Since the resistance in B. tenagophila has a dominant
character, and also thinking in obtaining a possible model
for transmission control, we initiated another kind of
study. Populations of resistant (Taim, RS) and suscep-
tible albino (Joinville, SC) B. tenagophila were maintained
together, at different proportions, with and without S.
The idea is to analyze the genic flux of the alleles in-
volved in the resistance character, and to evaluate the
hypothesis related to the selective advantage for the re-
248B. tenagophila: dynamics of populations • Florence Mara Rosa et al.
sistant lineage when compared with the susceptible one,
when both are under S. mansoni pressure.
MATERIALS AND METHODS
Snails - The pigmented B. tenagophila Taim strain,
that was originally collected at the Ecological Station at
Taim, state of Rio Grande do Sul, Brazil, has been completly
resistant to experimental infection with S. mansoni (Santos
et al. 1979). This strain has been maintained at the Labo-
ratory of Schistosomiasis, Department of Parasitology,
UFMG, Brazil, for more than 27 years, without any kind of
selecting favoring the resistance character, since these
snails are naturally resistant to S. mansoni. The albino B.
tenagophila strain was originally collected at Joinville
area, state of Santa Catarina, Brazil, by Dr Lobato Paraense
that kindly provided the Joinville snail strain to be used in
our experiments. In previous experiments, we observed
that B. tenagophila Joinville was highly susceptible to
different S. mansoni strains, such as S. mansoni SJ – iso-
lated from infected snails from São José dos Campos/SP
and S. mansoni LE – isolated from an infected pacient
from Belo Horizonte/MG.
Parasite - The LE strain of S. mansoni, isolated from a
patient in Belo Horizonte, Minas Gerais, Brazil, was used
in all the experiments described bellow. This parasite strain
has been maintained by successive passages through B.
glabrata and hamsters (Mesocricetus auratus).
Cross-breeding -Ten parental groups were assembled
with 50 young snails, measuring 3-4 mm of shell-diameter,
placed into plastic vessels with approximately 30 l dechlo-
rinated water and fed with lettuce. Each group consisted
of B. tenagophila Taim and/or B. tenagophila Joinville in
the following proportions: Group 1: 50 pigmented B.
tenagophila Taim (only parasite resistant snails); Group
2: 50 albino B. tenagophila Joinville (only parasite sus-
ceptible snails); Group 3: 25 resistant snails and 25 sus-
ceptible snails; Group 4: 40 susceptible snails and 10 re-
sistant snails; Group 5: 40 resistant snails and 10 suscep-
tible snails. The groups 1-5 were not infected. The groups
6-10 were assembled with the same snail proportion than
groups 1-5, however the groups 6, 7, 8, 9, and 10 were
submitted to the parasite pressure, as detailed bellow. The
cross-breedings are summarized in Table I.
Each group was kept for 60 days, so the snails could
reach sexual maturity. After this period, the snails of groups
6 to 10 were infected with S. mansoni miracidia every week,
for 8 weeks, and the fecundity parameters and survival
rates of each group were analyzed for 10 consecutive
weeks.Fifty pigmented F1 snails, randomly obtained from
each parental group, were assembled in 10 new groups to
obtain the F2 generation. This F2 progeny was kept and
analyzed as described for the parental group.
Fecundity parameters - After the snails had reach
sexual maturity, styrofoam strips were placed on the wa-
ter surface of each plastic vessel, to be used as support
for snails egg-masses deposition. The styrofoam strips
were recovered weekly, and replaced by new ones to evalu-
ate the group fecundity. The strips were analyzed under
stereomicroscope and the number of egg-masses, the num-
ber of eggs/egg masses and number of eggs/snail were
estimated for each group during 10 consecutives weeks
of examination. In case of need, the results were statis-
tically compared, the Wilcoxon test being used for the
non-parametric data, and the paired Student’s “t” test for
the parametric ones. The total number of the surviving
snails in each experimental group and the phenotypic
parameter (pigmentation) were analized 30 days after
Snail infection - The snails were infected with mira-
cidia of S. mansoni isolated from livers of hamster in-
fected for 45-50 days, according to Pellegrino and Katz
(1968). For the infection of breeding groups 6 to 10, the
miracidia were counted and added directly to the vessels
where the snails were kept. Each group received 200
miracida/week and the infection was accumulative, since
this procedure was performed for 8 consecutive weeks.
To test susceptibility level of F1 and F2 progenies, 50
young individuals (3-4 mm) of each cross-breeding were
exposed to S. mansoni infection. For this purpose, each
snail was individually exposed to 30 miracidia.
Methods for analysis of snail infection - Aiming at
verifying the emergence of S. mansoni cercariae, the F1
and F2 infected snails were individually observed under a
stereomicroscope, every week between 40 and 90 days
after exposure to miracidia. For examination of cercarial
shedding, each snail was kept in small Snap-cap glass
recipients, with dechlorinated water, and exposed to arti-
ficial light for 2 h (Pellegrino & Katz 1968). After this pe-
riod, the negative snails were squeezed between slide and
coverslip in search for sporocysts.
In this study, it was verified that S. mansoni is a nega-
tive factor of selective pressure for the susceptible popu-
lation. As can be observed in Fig. 1A, the individuals
pertaining to B. tenagophila Taim (Group 1) or Joinville
(Group 2) populations had a high survival rate, 90 and
97 % respectively, when the populations were kept iso-
lated and not exposed to parasite infection. In contrast,
the survival rate of B. tenagophila Joinville dropped to
60% when the snail population was exposed to the para-
site (Group 7), whereas no difference in the survival rate
of B. tenagophila Taim was detected after parasite infec-
tion (Group 6).
Schedule of the parental groups submitted or not to
Schistosoma mansoni pressure
Uninfected groupInfected group
R: resistant pigmented (B. tenagophila Taim); S: susceptible albino
(B. tenagophila Joinville).
249 Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 101(Suppl. I), 2006
In breeding groups composed by mixed population of
B. tenagophila Taim and Joinville, parasite infection also
resulted in decreased survival rate of S. mansoni suscep-
tible snails (Fig. 1B, C, D). However, in this mixed snail
population, where the proportion of Taim and Joinville
was similar or had more Joinville (Fig. 1B, C), Taim snails
had survival rate inferior to 50%, irrespective of the para-
site infection. In contrast, in the mixed snail population
with higher proportion of Taim stain, the survival rate of
the resistant snail was elevated (70-80%), while only 50%
of the B. tenagophila Joinville population were able to
survive after parasite exposition.
The B. tenagophila Taim was more fecund than B.
tenagophila Joinville (Table II). Significant differences (p
= 0.0039) could be observed when the number of eggs/
snail in Group 1 (B. tenagophila Taim) was compared with
Group 2 (B. tenagophila Joinville). The same occurred
when the number of eggs/snail in those two populations
was analyzed, presenting p < 0.014 as a result (groups 6
and 7). The number of eggs/egglaying in Groups 1 and 2
was not significant, conversely Groups 6 and 7 presented
highly significant values (p = 0.0001). When we com-
pared the fecundity parameters of the infected suscep-
tible population (Group 7) and those ones of the
uninfected population (Group 2), a decrease could be
observed, mainly in the number of eggs in the infected
group, but the values were not significant. It appears that
the parasite was unable diminishing significantly the
egglaying in the infected snails. When both populations
were compared, the number of surviving F1 descendants
of B. tenagophila Taim was higher than those ones of B.
tenagophila Joinville. The high proportion of pigmented
snails obtained in F1 and F2 generations in the groups 3,
4, 5, 8, 9 and 10, suggested that cross-breeding between
pigmented B. tenagophila Taim and albino B. tena-
gophila Joinville populations occurred (Tables III, IV).
The F1 and F2 progeny obtained from cross-breeding
group containing only B. tenagophila Joinville showed
susceptibility rate to S. mansoni infection superior to 55%,
similarly to the susceptilibity rate observed in parental
group, while the complete resistance of B. tenagophila
Taim was confirmed through the generations (Table V).
F1 generation obtained by cross-breeding between resis-
tant and susceptible lineages was completely resistant to
S. mansoni infection, irrespective of the Taim proportion.
Moreover, less than 5% of F2 progeny were susceptible to
S. mansoni infection. Therefore, even with higher mortal-
ity rate of parental group, B. tenagophila Taim snails pre-
sented a markedly better reproductive performance and
were able to transmit the resistance character to their de-
scendants. The results obtained with F1 and F2 genera-
tions after the susceptibility trial corroborate this hypoth-
Fig. 1: surviving rate of Biomphalaria tenagophila Taim (R) and B. tenagophila Joinville (S) populations, submitted or not to Schistosoma
mansoni pressure. A: G1-50 R and G2-50 S without infection; G6-50 R and G7-50 S with infection; B: G3-25 R + 25 S without infection;
G8-25 R + 25 S with infection; C: G4-10 R + 40 S without infection; G9-10 R + 40 S with infection; D: G5-40 R + 10 S without infection;
G10-40 R + 10 S with infection.
250B. tenagophila: dynamics of populations • Florence Mara Rosa et al.
Throughout an 18-month-experimental period, we stud-
ied the populational dynamics of resistant and suscep-
tible strains of B. tenagophila. The two populations were
maintained together, at different proportions of individu-
als, with and without S. mansoni pressure. The first point
to be discussed is the question about the natural selec-
tion in those two populations. The presence of S. mansoni
in susceptible snails represents a disease with devastat-
ing effects, since it causes a high mortality in the infected
snails and a decrease in the egg-laying, thus becoming an
element of natural selection, which is highly negative for
the potentially transmitter snails of schistosomiasis
(Coelho 1995). The lineage of B. tenagophila Joinville
suffers the effect of infection, and this was observed due
to the high mortality rate and a slight reduction in the
number of eggs per snail in this population.
It could be observed that the parental populations
submitted to pressure of the parasite presented a lower
number of albino F1 individuals, when compared with the
uninfected groups. Probably, this result could be related
to reduction of the susceptible albino parental popula-
tion itself. This experiment underwent the interference of
another factor, possibly competition (Groups 3, 8, 4, 9). B.
tenagophila Taim lineage presented on the one hand a
drawback, i.e., a higher mortality rate without pressure of
the parasite. On the other hand, this lineage presented a
markedly a superior reproductive capacity studies car-
ried out in our laboratories confirmed that B. tenagophila
Taim was more fecund than B. tenagophila Joinville. This
can be accounted for by the fact that a higher number of
F1 surviving snails from B . tenagophila Taim population
In all groups, the individuals pertaining to F1 genera-
tion were almost all predominantly pigmented. The pro-
portion between pigmented and albino individuals de-
tected in F2 generation showed that a cross-breeding oc-
curred between parenteral B. tenagophila Taim × albino
B. tenagophila Joinville. The recessive albino character
was used, in this case, as a phenotypic marker, which
facilitates distinction between F1 individuals generated
by cross-breeding (all of them being pigmented) and those
ones generated by self-fecundation (albino). Paraense
Mean fecundity per week, in the parental breeding-group and total number of surviving F1 individuals after 30 days hatching
Number of Number ofNumber of
Group egg-masses eggs egg-masses per snail eggs/snail
Number of Number of
Total number of
surviving F1 individuals
Percentage of pigmented and albino F2 progeny snails obtained
by cross-breeding between adult F1 X F1
Parental group% pigmented% albino
Susceptibility rate of F1 and F2 pigmented snails individually
infected with Schistosoma mansoni
snails % (F1)
snails % (F2)
Percentage of pigmented and albino F1 progeny snails obtained
by cross-breeding between susceptible and resistant adult snails
Parental group% pigmented% albino
251 Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 101(Suppl. I), 2006
(1955) demonstrated that those individuals performed self-
fecundation only when they were isolated, otherwise they
always preferred cross-breeding (when in the presence of
one or more individuals).
Analyzing the resistance phenotype of F1 and F2 indi-
viduals, it was observed that, in this experiment, a pre-
dominance of resistant individuals occurred in all groups.
Lewis et al. (2002) analyzed the genic flux of the resis-
tance character in F1 descendants generated by cross-
breeding between a resistant strain of B. glabrata and a
susceptible one of the same species. The results obtained
showed that the number of resistant F1 individuals was
higher than the number of susceptible ones. Based on the
results obtained in this study, and taking into account
studies carried out on the resistant B. tenagophila Taim
strain throughout the last 27 years, our research group
proposes a biological control model for schistosomiasis.
The idea is to introduce the genetic characters of the re-
sistant strain into the susceptible populations in endemic
areas maintained by B. tenagophila (Coelho et al. 2004).
It is expected that after a drastic reduction of the local
population in the transmitter focus as, for example, after
the use of moluscicide, the introduction of the resistant
Taim lineage on a large scale would force the surviving
individuals to perform cross-breeding with the introduced
lineage. Their descendants would be endowed with the
desired dominant character of resistance to the parasite,
and would inherite the adaptative capacity to the local
environment of their local ascendants as well.
The molecular marker, which is typical of the Taim lin-
eage, although being not associated to resistance, has a
dominant character too (Rosa et al. 2004). This marker is
represented by the band with 350 bp of the ITS region of
the ribosomal mitochondrial DNA detected by PCR-RFLP
technique, using Ddel I enzyme. This marker will be of
great importance for the follow-up, and to demonstrate
the success obtained with the insertion of the genetic
characteristics of the Taim lineage into the population
after intervention. This model has been already used in
focuses located in Bananal and Caraguatatuba – two cit-
ies in the state of São Paulo, Brazil, in a collaborative work
with Sucen, UFMG, and Fiocruz. In those focuses, molus-
cicides were not previously used. This experimental ap-
proach was approved by Ibama, the Brazilian official
agency that control environmental interventions.
The success of introduction of the genetic charac-
teristics of resistance will be confirmed by the presence
of the molecular marker of Taim lineage in the snails born
after intervention, and by means of tests related to sus-
ceptibility to S. mansoni carried out with these progenies,
when compared with those ones of the local strain, that
was isolated before introduction of the Taim lineage.
To Dr Maria Lúcia Prado Uchôa Maciel, owner of the
“Chácara Santa Inês”, Bananal/SP, to the Biologist Marta Leonia
Valiante, as well as to the technicians João Batista dos Santos,
Jefferson Bernardes do Carmo, and Selma Fernandes de Souza.
To Mirian Ferreira de Oliveira Bruno, Prefect of Bananal, state
of São Paulo, for her valuable support to our project.
Coelho PM 1995. Resistência e suscetibilidade à infecção por
Schistosoma mansoni em caramujos do gênero Biom-
phalaria. In FS Barbosa, Tópicos em Malacologia Médica,
Fiocruz, p. 208-217.
Coelho PMZ, Carvalho OS, Andrade ZA, Martins-Sousa RL,
Rosa FM, Barbosa L, Pereira CAJ, Caldeira RL, Passos LJ,
Godard ALB, Moreira LA, Oliveira GC, Franco GR, Teles
HMS, Negrão-Côrrea D 2004. Biomphalaria tenagophila/
Schistosoma mansoni interaction: premises for a new ap-
proach to biological control of schistosomiasis. Mem Inst
Oswaldo Cruz 99 (Suppl.1): 109-111.
Freitas JR, Boschi MB, Santos MBL 1985. Suscetibilidade de
“híbridos” de Biomphalaria tenagophila à cepa LE (BH)
do Schistosoma mansoni. Rev Inst Med Trop São Paulo 1:
Lewis AF, Patterson CN, Grzwacz C 2002. Parasite- suscepti-
bility phenotypes of F1 Biomphalaria glabrata progeny
derived from interbreeding Schistosoma mansoni-resistant
and susceptible snails. Parasitol Res 89: 98-101.
Paraense WL 1955. Autofecundação e fecundação cruzada em
Australorbis glabratus. Mem Inst Oswaldo Cruz 53: 277-
Paraense WL, Corrêa LR 1978. Differential susceptibility of
Biomphalaria tenagophila populations to infection with a
strain of Schistosoma mansoni. J Parasitol 64: 822-826.
Paraense WL, Corrêa LR 1987. Probable extension of schisto-
somiasis mansoni to southern Brazil. Mem Inst Oswaldo
Cruz 82: 577.
Pellegrino J, Katz N 1968. Experimental chemotherapy of schis-
tosomiasis mansoni. Adv Parasitol 6: 233-290.
Rosa FM, Caldeira RL, Carvalho OS, Godard ALB, Coelho
PMZ 2004. Dominant character of the molecular marker of
Biomphalaria tenagophila (Mollusca: Planorbidae) strain,
resistant to Schistosoma mansoni. Mem Inst Oswaldo Cruz
Rosa FM, Godard ALB, Azevedo V, Coelho PMZ 2005.
Biomphalaria tenagophila: dominant character of the resis-
tance to Schistosoma mansoni and descendants of cross-
breeding between resistant (Taim, RS) and susceptible
(Joinville, SC) strains. Mem Inst Oswaldo Cruz 100: 19-23.
Santos MBL, Freitas JR, Correia MCR 1979. Suscetibilidade
ao Schistosoma mansoni de hibridos de Biomphalaria
tenagophila do Taim, RS, Cabo Frio, RJ, e Belo Horizonte,
MG. Rev Inst Med Trop São Paulo 21: 281-286.
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