# Infection with metacercaria of Clinostomum complanatum (Trematoda: Clinostomidae) in freshwater fishes from Southern Caspian Sea Basin

F Aghlmandi, F Habibi, M A Afrai, A Abdoli, S Shamsi

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F Aghlmandi, F Habibi, M A Afrai, A Abdoli, S Shamsi. Infection with metacercaria of Clinostomum complanatum (Trematoda: Clinostomidae) in freshwater fishes from Southern Caspian Sea Basin. Revue de Médecine Vétérinaire, 2018, 7-9 (169), pp.147-151. hal-05046368

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# Infection with metacercaria of *Clinostomum complanatum* (Trematoda: *Clinostomidae*) in freshwater fishes from Southern Caspian Sea Basin

F. AGHLMANDI<fnref n="1" />, F. HABIBI<fnref n="1" />, M. A. AFRAII<fnref n="1" />, A. ABDOLI<fnref n="2" />, S. SHAMSI<fnref n="3" />*

## SUMMARY

Clinostomum complanatum is a digenetic food borne trematode that is known to heavily infect fish-eating birds in northern Iran, adversely affecting their health. We performed the present study to investigate the infection status of freshwater fish with digenetic trematode metacercariae (C. complanatum) in the water systems of Shiroud, Tajan and Gorganroud Rivers of the Southern Caspian Sea Basin, Iran. A total of 849 fish belonging to 9 species were examined, namely *Alburnus alburnus*, *A. chalcoides*, *Alburnoides bipunctatus*, *Barbus plebejus*, *Capoeta gracilis*, *Carassius auratus*, *Squalius cephalus*, *Neogobius fluviatilis* and *Cobitis cf taenia*. Of these, only fish in the Shiroud River were found to be infected with the parasite, with the species *Alburnoides bipunctatus*, *Capoeta gracilis*, *Cobitis cf taenia* and *Squalius cephalus* being affected. To the best of the authors' knowledge, this is the first time that *Alburnoides bipunctatus* and *Cobitis cf taenia* have been recorded as intermediate hosts of this parasite. Metacercariae were found mostly under the skin of the fish; however, one metacercariae was found in the brain of *A. bipunctatus*, with a curled tail suggesting that the parasite is able to migrate to the vital organs of fish and consequently affect their functions. To confirm the identity of the metacercariae, they were fed to two chickens to obtain adults which were identified as *Clinostomum complanatum*. The Shiroud River runs through highly populated areas and is the centre of major fishery activities, therefore the high prevalence of a zoonotic parasite such as *C. complanatum* in its fish is of high significance, particularly in light of the local diet, which occasionally includes smaller fish that are consumed whole and raw. It is suggested that fisheries and medical authorities in the region take the initiative to inform local farmers and the public about the potential risk that *C. complanatum* may pose to fish farms and public health.

**Keywords:** Clinostomum complanatum, Fish, Prevalence, Caspian Sea, Zoonose

## RÉSUMÉ

Infection par métacercaires de *Clinostomum complanatum* (Trematoda: *Clinostomidae*) chez les poissons d'eau douce du Bassin Sud de la Mer Caspienne

Un parasite digénien, *Clinostomum complanatum*, contamine fortement les oiseaux piscivores dans le Nord de l'Iran, et nuit à leur santé. L'objectif de cette étude était de découvrir le stade durant lequel les poissons locaux sont contaminés par le parasite. Au total, 849 poissons appartenant à 9 espèces furent examinés pour contamination par les métacercaires de *C. complanatum*. Seuls les poissons de la rivière Shiroud étaient contaminés par le parasite, y compris *Alburnoides bipunctatus*, *Capoeta gracilis*, *Cobitis cf taenia* et *Squalius cephalus*, peut-être dû à la présence d'un premier hôte intermédiaire adéquat dans la région. A ce jour, l'identité exacte de ce premier hôte intermédiaire pour ce parasite communément trouvé en Iran est inconnue. La rivière Shiroud traverse des régions fortement peuplées et est un centre majeur de pêche ; par conséquent, la forte prévalence d'un parasite zoonotique tel que *C. complanatum* dans ses poissons est d'une grande importance, compte tenu notamment du fait que l'alimentation locale comprend occasionnellement des petits poissons entiers ou crus. Nous présentons *Alburnoides bipunctatus* et *Cobitis cf taenia* en tant que nouveaux hôtes pour le parasite. Il s'agit également du premier signalement des métacercaires de *C. complanatum* dans le cerveau d'un poisson, *Alburnoides bipunctatus*, avec la queue courbée démontrant la capacité du parasite à migrer vers les organes vitaux du poisson et affectant leurs fonctions. Il est recommandé que les autorités médicales et pêcheries de la région prennent les initiatives pour informer les fermiers locaux et le public au sujet des risques potentiels que *C. complanatum* puisse poser aux pêcheries et à la santé publique.

**Mots-clés :** Clinostomum complanatum, poisson, la Mer Caspienne, zoonos

## Introduction

It is well known that freshwater fish are not only a major source of protein for humans but also common intermediate hosts for different parasitic species. The metacercariae of digenetic trematodes are considered to be one of the most prevalent parasitic species infecting fish. They can cause low weight gain, low unmarketability and high mortality, and some may also have zoonotic importance.

*Clinostomum complanatum* is a hermaphroditice parasite with an indirect life cycle. The adult worms typically live in the oral cavity and oesophagus of piscivorous birds which become infected after consuming infected fish or amphibians

[7]. Metacercariae of *C. complanatum* are large, often yellow and encyst in a variety of sites in the body such as the oral cavity, gills, intestines, tail, muscles and eye sockets of fish or amphibians, causing the well-known "yellow grub disease". In humans, when infection occurs after the consumption of raw fish, the fluke accidentally attaches to the surface of the mucus membrane of the throat, causing a clinical syndrome called *halzoun*. Many cases have been described in several countries, including Japan, Korea, Thailand and India [2, 11, 15, 20] and it is considered to be an important parasitic zoonosis for public health in these countries [9]. Although no human cases have yet been reported in Iran, this could be due to a health practitioner's lack of knowledge about the occurrence of this parasite in local fish and/or substandard

<footnote n="1">¹Department of Aquatic Animal Health, Caspian Sea Ecological Research Centre, Sari, Iran</footnote>

<footnote n="2">²Shahid Beheshti University, Tehran, Iran</footnote>

<footnote n="3">³School of Animal and Veterinary Sciences, Graham Centre for Agricultural Innovation, Charles Sturt University, Australia</footnote>

<footnote>*Corresponding author: sshamsi@csu.edu.au</footnote>
documentation and recording of human health data in the country.

There is a high prevalence of this zoonotic parasite in the relatively large populations of birds that exist in northern Iran, an area that also has a dense human population among whom seafood is popular [16]. Therefore, we were prompted to carry out the present study with the aim of finding the intermediate fish hosts of *C. complanatum*. Many rivers in the region are home to a broad variety of freshwater and anadromous fish species. Several commercially valuable fish species, such as *Rutilus frisii* (also known as Caspian kutum) and sturgeon migrate seasonally to breed and spawn. Many of these fish are edible and local diets may include the consumption of raw or undercooked small fish, either whole or in parts.

# Materials and methods

## STUDY AREA

Fish were collected from three rivers within the southern coast of the Caspian Sea Basin (Fig. 1) during the summer months. The Caspian Sea is the largest enclosed inland body of water on Earth by area. Iran has three highly populated provinces located on its southern coast, the populations of which have grown steadily during the last decades. It is estimated that at least 10 million people live in the southern Caspian Sea Basin. The region is bordered by Alborz Heights in the south, which also is responsible for its semitropical climate. Several rivers flow into the basin that are inhabited by numerous fish species from six families [14], which makes it one of the most important and primary production areas in Iran. These rivers are known to be the main spawning ground for several of Iran's commercially valuable fish. Due to high rainfall, the rivers flow rapidly throughout the year. There are

several private and government fish farms along the rivers or in close proximity to them. Table 1 shows details of the fish collected and their localities. The nomenclature of the fish investigated in the present study is based on Keivany et al. [10].

<figure><img src="image_2.png" /><figcaption>FIGURE 1: Three locations where fish were sampled from, including downstream of Shiroud River (1), Upstream of Tajan River (2) and downstream of Gorganroud (3).</figcaption></figure>

## FISH AND PARASITOLOGICAL EXAMINATION

Fish were transferred to a laboratory in ice and were examined for infection with parasites according to standard protocols [5]. In the laboratory, all fish were first visually examined for any unusual features on their surface. Fish then were incised, transferred into a petri dish, tray or similar container and examined for anything unusual. They were cut open using sharp scissors from the anus to the area between the pelvic fins. The body wall was removed on the left side

<table><caption>TABLE I: List, number and location of sampling for fish examined in the present study. Numbers after rivers' name corresponds to the numbers in Figure 1.</caption><thead><tr><th>Family</th><th>Common name</th><th>Scientific name</th><th>Shiroud River (1)</th><th>Tajan River (2)</th><th>Gorganroud River (3)</th><th>Total</th></tr></thead><tbody><tr><td>Cobitidae</td><td>Spined loach</td><td>Cobitis cf taenia</td><td>101</td><td>35</td><td>-</td><td>136</td></tr><tr><td rowspan="7">Cyprinidae</td><td>Bleak</td><td>Alburnus alburnus</td><td>5</td><td>1</td><td>-</td><td>6</td></tr><tr><td>Danube bleak</td><td>A. chalcoides</td><td>12</td><td>2</td><td>1</td><td>15</td></tr><tr><td>Schneider</td><td>Alburnoides bipunctatus</td><td>101</td><td>30</td><td>9</td><td>140</td></tr><tr><td rowspan="2">Barbel</td><td>Barbus plebejus</td><td>7</td><td>5</td><td>-</td><td>12</td></tr><tr><td>Capoeta gracilis</td><td>103</td><td>100</td><td>72</td><td>275</td></tr><tr><td>Goldfish</td><td>Carassius auratus</td><td>68</td><td>65</td><td>29</td><td>162</td></tr><tr><td>Chub</td><td>Squalius cephalus</td><td>6</td><td>2</td><td>-</td><td>8</td></tr><tr><td rowspan="2">Gobiidae</td><td rowspan="2">Monkey goby</td><td>Neogobius fluviatilis</td><td>77</td><td>16</td><td>2</td><td>95</td></tr><tr><td>Total</td><td>480</td><td>256</td><td>113</td><td>849</td></tr></tbody></table>
by making an incision above the pectoral fin and cutting along the lateral line to the anus. Before examining any organ for parasite infection, the outer layers of all internal organs, including the gut, gonads, swim bladder, liver, kidneys, pyloric caeca and heart were thoroughly visually examined for the presence of parasites.

Metacercariae were recovered from cysts using a sharp needle and fixed between two slide glass slides with 70% ethanol. The infected organs, number of cysts per fish and other important data such as the fish's species and locality were recorded. Later, the metacercaria were stained with carmine. After de-staining in acid alcohol, they were dehydrated in alcohol series, cleared in xylol and mounted in Canada balsam. Drawings were made to scale with the aid of a camera lucida and measurements were made directly with an eyepiece micrometer, including body size, and oral sucker and acetabulum length and width. According to their morphological characteristics, parasites were identified to genus level [1]. Parasite prevalence and intensity were calculated according to Shamsi and Suthar [17].

## EXPERIMENTAL INFECTION OF BIRDS

For specific identification, some live metacercariae were obtained from fish and fed to two 20-day old chickens. Although those chickens had never been fed with seafood of any sort, their faeces were examined for infection with parasite eggs prior to experimental infection to ensure no previous infection existed. After 5 and 7 days, chickens were euthanized by an overdose of clove oil and examined for infection with parasites. Parasites were collected in accordance with Shamsi et al. [16] and then processed in the same manner as metacercaria, i.e., preserved in ethanol and stained with carmine.

## Results

Both the Tajan and Gorganrud Rivers are the major rivers in the southern Caspian Sea area. Some 256 fish belonging to nine species (Table 1) were examined from the Tajan River and 113 fish from belonging to five species (Table 1) were examined from Gorganroud River. None of these fish were found to be infected with metacercaria of *C. complanatum*. In Shiroud River, 480 fish belonging to nine species were examined of which four species, including *Alburnoides*

*bipunctatus*, *Capoeta gracilis*, *Cobitis cf taenia* and *Squalius cephalus*, were found to be infected with metacercaria of *C. complanatum* (Table 2). The highest rate of infection (24.3%; *n* = 103) was observed in *Capoeta gracilis*, followed by *Squalius cephalus*, *Alburnoides bipunctatus* and *Cobitis cf taenia*. The present investigation also found that fishes from Shiroud River were more heavily infected with *C. complanatum* than those from the other study sites.

The encapsulated metacercariae were found mostly under the skin, on the gills and within muscle tissues. The maximum number of metacercaria per fish (84) was found in a *Capoeta gracilis*. In one *A. bipunctatus*, with an abnormally curved spinal cord, a metacercaria was found in its brain.

All metacercariae found in the present study (Fig. 2) had similar morphology with an average length of 4.75 cm (*n* = 10) and width of 2.34 cm. Oral collars were visible. Ventral suckers (mean = 0.81 × 0.84 cm) were larger than oral suckers (mean = 0.31 × 0.43 cm). Intestinal caecae were lateral to ventral suckers and genital complexes. Testes (mean = 0.29 × 0.73 and 0.41 × 0.99 cm, for anterior and posterior testes, respectively) and ovaries (mean = 0.11 × 0.14 cm) were present.

<figure><img src="image_3.png" /><figcaption>FIGURE 2: showing metacercariae of *C. complanatum* found in the present study. Scale bar = 500 µm.</figcaption></figure>

<table><thead><tr><td>Fish</td><td>No of examined fish</td><td>No of infected fish (frequency %)</td><td>Min./max. no of parasites per fish</td><td>Intensity<sup>1</sup></td></tr></thead><tbody><tr><td>Alburnoides bipunctatus</td><td>101</td><td>8 (7.9)</td><td>1-4</td><td>1.9</td></tr><tr><td>Capoeta gracilis</td><td>103</td><td>25 (24.3)</td><td>1-84</td><td>9.8</td></tr><tr><td>Cobitis cf taenia</td><td>101</td><td>5 (4.9)</td><td>1-2</td><td>1.8</td></tr><tr><td>Squalius cephalus</td><td>6</td><td>1 (16.6)</td><td>2-2</td><td>2.0</td></tr></tbody></table>

<caption>TABLE II: Infection status with *C. complanatum* metacercariae in fresh-water fishes collected from Shiroud River, Iran.</caption>

<footnote n="1">¹Intensity = number of parasites/number of infected fish</footnote>
Adult worms were recovered from the mouths and pharynxes of the experimentally infected chickens. Microscopy and examination of the adults revealed their specific identity as *C. complanatum* according to Grabda-Kazubska [7] and Shamsi et al. [16].

Discussion

Despite examining fish from a broad geographical
distance in the region (over 300 km; Fig. 1), only fish
collected from Shiroud River were found to be infected
with *C. complanatum* (Table 2). Although some fish, such
as *Capoeta gracilis* and *Alburnoides bipunctatus*, were
collected and examined from all three rivers (Table 1),
only those collected from Shiroud River showed infection
with the parasite, suggesting that only the Shiroud River
has suitable environmental and/or biological factors for the
completion of the parasite's life cycle. A previous study [16],
also conducted in the southern Caspian Sea Basin, showed
that piscivorous birds can be heavily infected with the adult
form of this parasite. Therefore, the results of the present
study suggest that parasite eggs are distributed across the
whole region through infected birds but can only reach fish,
their second intermediate hosts, in the Shiroud River region.
The climate of the study area is highly varied, being dry near
Gorganroud River and subtropical near Shiroud River (Fig.
1). For example, the annual rainfall in the Gorganroud River
area, located in the eastern side of the southern Caspian Sea
Basin, ranges between 18 to 88 mm, while that of the Shiroud
River region, located on the western side of the Southern
Caspian Sea Basin, is 29 to 210 mm. This dramatic difference
may affect the survival of parasite eggs and miracidium
which require an aquatic environment to survive and snails
as the first intermediate host. Given that both the infected
fish in the present study and birds in the previous study
[16], including *Ardea purpurea*, *Egretta alba*, *E. garzetta* and
*Nycticorax nycticorax* have wide geographical distributions
in the region and can also be found elsewhere, it is possible
that the limited geographical distribution determined for
this parasite in northern Iran is due to a limited distribution
of suitable first intermediate hosts, i.e., snails. Currently,
the first intermediate host(s) for *C. complanatum* in the
region is (are) not known. It is only known that cercariae of
*Clinostomidae* have been reported in *Lymnaea gedrosiana*
[19]. Therefore, one important area for future study would be
in the determination and specific identification of the natural
first intermediate host(s) for the parasite in the region.

In other countries, metacercaria of *Clinostomum* have
been reported in a wide variety of freshwater fish (the second
intermediate host), as well as toads, frogs, salamanders and
tritons. In Iran, *C. complanatum* has previously been reported
in five species of fish from other regions, including *Aphanius
aphanius* [8], *A. dispar* [6], *Chalcalburnuc chalcoides* [4],
*Capoeta gracilis* and *Pseudorasbora parva* [13]. These fish are
from various zoogeographical regions and from a variety of
fish families suggesting that, as pointed out by several other
studies [12], the metacercariae of *C. complanatum* have

broad host specificity, making the findings of the present
study significant due to the potential impacts on farmed fish
and public health.

From a fish health impact point of view, the present
study's finding of *C. complanatum* metacercariae in the brain
of *Alburnoides bipunctatus* is significant, as it shows the
ability of the parasite to migrate to the vital organs of fish
and, consequently, adversely affect their function. It would
have been interesting to investigate the histopathology of the
brain in the infected fish; however, due to the condition of the
fish, which had been euthanized some time previously, the
brain tissue was not suitable for histological study. In gross
examination, the fish was found to have a curved spinal cord.
We did not find any other parasites that are known to cause a
similar effect, such as myxosporeans, in this fish. It is known
that infection of fish by *Clinostomum* can result in behavioural
changes, disease and death resulting in economic loss for
fishing industries. Previous histopathological studies showed
that metacercariae can cause infiltration of the immune cells
at the site of cyst attachment, degenerative changes in the
tissues around the cyst [18] and even mortality due to higher
predation rate [3].

More importantly, *C. complanatum* is known to be
zoonotic [15, 20]. The metacercaria is the infective stage.
Humans become infected by consuming infected fish.
Therefore, the high prevalence and abundance of parasite
metacercaria found in edible fish from the Shroud River
are of high significance. The landscape of the lower reaches
of this river is dominated and influenced by the city of
Tonekabon, which has a population of over 200,000. The
Shiroud River basin is located in the central sector consisting
of 33,000 people living in 135 residential areas and villages
[14]. More than 30 of these villages are located on the banks
of the Shiroud River and, thus, there are direct interactions
between people and the river. Interestingly, in the local area,
it is believed that consumption of small freshwater fish is
a natural remedy for jaundice, a disease that is relatively
common among locals, particularly children. Small-sized
fish are also quite commonly consumed whole, where
internal organs such as the brain may remain undercooked.
This greatly increases the risk of infection with this zoonotic
parasite among the local population. The symptoms caused by
infection with *C. complanatum* after consuming raw or semi-
cooked infected fish varies between humans, making accurate
diagnosis difficult, particularly as local medical doctors
are not usually aware of this parasite. The most common
condition is laryngopharyngitis where metacercariae firmly
attach to the mucous membrane of the pharynx [11]. Injury
to other organs such as the oesophagus due to attachment of
metacercariae, anaemia and eye infections are among other
conditions assigned to infection with the metacercariae of
*C. complanatum* in humans [20]. Since local people are not
aware of these parasites and the consequences of consuming
infected fish, it is suggested that fisheries authorities in the
region take the initiative to inform local fish farmers about
preventing farmed fish becoming infected with this parasite
by controlling snail and bird populations in local aquaculture
systems. Medical authorities also should take the initiative to
educate medical practitioners and the public about the risk
C. complanatum may pose to public health.

Acknowledgement

We are grateful to Dr Celia Barril, from School of
Agricultural and Wine Sciences & National Wine and Grape
Industry Centre in Charles Sturt University for the French
summary of this manuscript. This study had partial financial
support from the Iranian Fisheries Research Organisation.
Animal ethic guidelines developed by the Iranian Fisheries
Research Institute were followed in this study.

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