摘要：Following the occurrence of two large outbreaks in Gilan province,
northern Iran, the public health importance of human fascioliasis has increased
significantly. The mixed infections of Fasciola gigantica and F. hepatica within
a given domestic animal individual suggest a very complicate picture of possible
circulation ways of the parasite and the possibility for humans to be infected
with both species. Elucidating these circulation ways is very critical for
understanding the epidemiology and transmission of the disease and being
ascertain how animals and humans enter the different liver fluke circulations in
this endemic zone. The main objective of the present study was to investigate
the distribution and natural infections of local lymnaeids, environmental
characteristics related to the disease transmission and determining the most
prevalent fasciolids and definitive hosts in human endemic areas of Gilan
province. Bandar-Anzali and Rasht are the most important endemic areas with most
of the cases of human disease during the epidemics and inter-epidemic periods.
Sheep raising is not normal in these regions, while cattle is the most common
definitive host. According to the data obtained from slaughterhouse observations
in Bandar-Anzali and Rasht, the main fasciolid in local cattle is F. gigantica.
Of 928 adult liver flukes collected from 13 infected livers of cattle, in Rasht
and Bandar-Anzali slaughterhouses, 91.1% were diagnosed as F. gigantica and 8.9%
as F. hepatica. L. gedrosiana and L. palustris were the most prevalent lymnaeid
snails in this endemic zone. It appears that L. truncatula is not prevalent in
Bandar-Anzali and Rasht and surroundings of these endemic cities. Of 4830
different snails studied, only seven L. gedrosiana were found to be infected
with larval stages (rediae and cercariae) of Fasciola sp. Experimental
infections of 15 common laboratory mice by metacercariae, obtained from those
naturally infected snails, were carried out and all trematodes recovered at
necropsy, 8 weeks post-exposure, appeared to be F. gigantica based on
morphology. The high temperature, moisture and rainfall during the year,
especially in Bandar-Anzali, support the establishment and transmission of the
disease in the zone. Although the species involved in human infections in
endemic areas of Gilan has been usually referred to as F. hepatica, the results
of this study as well as some interesting epidemiological evidences related to
the disease, support that Fasciola gigantica might be the main causal agent of
fascioliasis in this important endemic zone.
