A total of 1479 fish classified into 30 species were collected during
the study period. Among them, 1316 (89%) comprised of 20
different species of the cyprinoid family and 163 (11%) belonging
to 8 families of non-cyprinoids (Table 1). Small liver fluke metacercariae
were recovered from 10 out of 20 cyprinoid families, but
none at all from fish of the non-cyprinoid families (Table 1).
The prevalence and the intensity of infection of 10 cyprinoid
fish species are summarized in Table 2. The prevalence varied from
2.1% to 66.7% depending on fish species, with the mean prevalence
of 17.5% in the total of 929 cyprinoid fishes. Among those,
Cyclocheilichthys apagon, Hampala dispar, Puntius brevis and Systomus
orphoides showed relatively high (>20%) prevalence. Although
Barbodes altus also showed high prevalence (66.7%), this result was
based on the examination of only 3 fish so that itwas not included in
further data analyses. The prevalence of other five cyprinoid species were <10%. Among four cyprinoid species having high prevalence of
infection, H. dispar and S. orphoides harboured more than 10 metacercariae
per fish, with the mean intensity of infection of 15.0 and
13.3, respectively (Table 2).
The distribution of metacercariae in the fish body was analyzed
for 4 cyprinoid fish with high prevalences (Table 3). In all four fish
species, metacercariae were preferentially found in the body muscles.
Especially >90% of metacercariae were found in the muscles
of H. dispar and S. orphoides, which showed high (>10 metacercariae/
fish) intensity of infection (see Table 2). Metacercariae were
also found in the pectoral and tail fins, but not in other fins except
for only one in the dorsal fin of a C. apagon.
Encysted metacercariae were oval in shape with 194±21.8m
long and 154±19.4m wide, and covered with a thin single layer of
cystwall. The metacercariae had large oral and ventral suckers with
a tubular excretory bladder at the posterior end, and were moving
actively in the cyst (Fig. 2A). A total of 25 and 26 adult worms
(the recovery rate of 83.3% and 86.7% respectively) were collected
from two hamsters experimentally infected with 30 metacercariae.
The adult worms were lancet-shaped, about 1 cm long, and were
morphologically identified as Opisthorchis viverrini (Fig. 2B). The
morphological identification of metacercariae and the adultworms
was confirmed further by genetic analyses. After alignment, the
genetic distances of the COI sequences of the collected metacercariae
to those of O. viverrini deposited in GenBank were 0–0.016,confirming that the collected metacercariae and the adults were O.
viverrini.
Subsequently the prevalence and the intensity of infection of
fishwere analyzed and compared based on fish-collection site—the
lake, outlet, and flood plain (Table 4). Because the fish species carrying
O. viverini metacercariae are limited to 10 cyprinoid species,
data analyses were performed on only those species. More than half
(60%) of the cyprinoid fish examined were collected from the lake,
but only 43 (13%) out of 492 cyprinoids from the lakewere found to
be metacercaria-positive. In contrast, 94 (29.7%) out of 316 cyprinoid
fish from flood plain and 24 (25.5%) of 94 cyprinoid fish from
the outlet canal were infected with O. viverrini metacercariae.
Related to the seasonal changes, the number of cyprinoid and
non-cyprinoid fish collected at every sampling time at three locations
(Fig. 3A), and the prevalence of metacercariae in fish were summarized in Fig. 3B. During May–August 2007, a dry season, fish
were only available from the lake and none of the fish harboured
metacercariae. From September 2007 to December 2008, a rainy
season, fish were collected from the lake and flood plain. During
this period, the outlet canal was under the flooded water. As shown
in Fig. 3B, during the rainy season, the prevalence of fish in flood
plain was fairly constant, while that of fish caught in the lake varied.
Although the sampling time and the number of samples on each time and location is not sufficient to draw any solid conclusion,
fish in the flood plain in the rainy season seemed to be constantly
infected with O. viverrini metacercariae.
การแปล กรุณารอสักครู่..
![](//thimg.ilovetranslation.com/pic/loading_3.gif?v=b9814dd30c1d7c59_8619)