Vibriosis

By Abisha

Vibriosis is one of the most prevalent fish diseases caused by bacteria belonging to the genus Vibrio.

Vibriosis (vibrio anquillarum complex) in milk fish – hemorrhage and inflammation of skin.

Vibriosis caused by Vibrio anguillarum 

Fish species affected:Mainly in marine culture of Salmonid and Perciformes fishVibriosis occurs in cultured and wild marine fish in salt or brackish water,

Seasonal occurrence:particularly in shallow waters during late summer

Vibriosis (vibrio anquillarum complex) in red grouper – inflammation and loss of scales.

Etiology

Vibrio anguillarum (mainly serotype I).

Family: Vibrionaceae.

Gram negative bacterium, appearing as a slightly curved rod with round edges polarly flagellated, bipolar staining. Motile in fresh suspensions in sterile saline 0.9%

The causative agent, of this Vibriosis disease: 

V. anguillarum, was first described in 1909 as the aetiological agent of the 'red pest of eels' in the Baltic Sea.

An earlier report from the early 1800's, describing epizootics in migrating eels (Anguilla vulgaris) implicated a bacterium named Bacillus anguillarum.

The pathology of the disease and the characteristics of the bacterium in these two reports suggested that the etiological agents were the same.

Vibriosis was not reported in North America until 1953, when V. anguillarum was isolated from chum salmon (Oncorhynchus keta).

Vibriosis in salmonids (vibrio anguillarum complex) in chinook salmon with lesion on body.

Vibrio anguillarum belongs to one of the halophilic groups of Vibrios and survives at different salinities.

it is able to survive in sea water for more than 50 months.

More than twenty different serovars of V. anguillarum (designated O1 to O23) have been described (Pedersen et al., 1999).

Serovars O1 and O2 occur world-wide and are those most often found in connection with diseases in fish particularly in salmonids and species of cod fish

All age classes are susceptible.

Mortality is higher among the young fry. Obviously, the economic damage is greater when larger growing bass are lost.

Age/size of fish mostly susceptible:

External & Internal SignsClinical Signs The characteristic clinical signs of Vibriosis include red spots on the ventral and lateral areas of the fish swollen and dark skin lesions that ulcerate, releasing a blood exudate.

There are also corneal lesions, characterized by an initial opacity, followed by ulceration and evulsion of the orbital contents.

However, in acute and severe epizootics, the course of the infection is rapid, and most of the infected fish die without showing any clinical signs.

Vibriosis disease occured in snapper

External haemorrhagic appearance of skin and fins, distended belly, inflamed anus  exophthalmus of diseased fish.

Pale liver with petechiae, splenomegaly distended intestines filled with yellowish transparent fluid comprise typical necropsy findings of vibriosis.

Often there is excessive visceral fat due to chronic overfeeding.

The swim bladder is frequently distended hence many of the moribund and dead fish float on the surface

Sometimes sea bass fry suffering vibriosis exhibit deep necrosis of the trunk of the tail peduncle and the caudal fin.

Cannibalistic activity against the sick fish by their cage-mates may predispose to such lesions

Necropsy findings

Diagnosisclinical symptoms, necropsy findings, isolation of the bacterium on agar plates (usually TSA or TCBS) and identification either biochemically (Biomerieux API system) or serologically by means of rapid agglutination test kits.

On TSA medium, incubated at room temperature (about 25°C), pale round colonies of about 1-1.5mm in diameter, develop within 24-36 hours.

A drop of the antiserum is placed on the dark field of the test card. A bacterial colony is taken from the agar plate with the loop and homogenised for 30 sec. with the antiserum. A positive agglutination is characterised by the formation of a multitude of small spherical agglutinates, whereas a negative test shows either no agglutinate formation, or irregularly shaped, cloudy agglutinates

Mono-Aqua diagnostic kit: It comprises a kit complete with reagents and necessary cards in order to perform a quick (30 sec) sero-agglutination test on bacterial colonies that have been isolated on agar plates from the tissues of sick or suspect fish in the laboratory.

Thus, it provides a fast and accurate identification of the pathogen bypassing the need to perform biochemical profiling..

The kit's main novelty lies in the fact that it provides an additional "negative control antiserum", that is, an antiserum that reacts against bacteria with close antigenic properties with Vibrio anguillarum

Abreviation ofmicrotube substrate Bacterial strain's biochemical

attributesResult Triad code

OPNG: ADH: LDC:

ODC: CIT: H2S:

URE:TDA:IND:

β-galactosidase productionArginine dihydrolase productionLysine decarboxylase production

Ornithine decarboxylase productionCitrate utilisationH2S production

Urease productionTryptophane deaminase productionIndole production

++--

--Variable

--

----+

3

0 or 2

4

Prevention and ControlGeneral Methods Control of furunculosis and vibriosis is best achieved by maintenance of water quality, good husbandry and low stocking densities.

This is not, however, always possible, and where outbreaks occur, treatment with antibiotics is the only option .

In areas where a disease is not endemic it is possible to exclude the causative agents by a legislative policy such as•1) restrictions on importation/movement of live fish/eggs and2) slaughter and disinfection in infected fish

Treatment:Daily administration of antibiotics, mixed in the feed, for 10 days is usually effective to eliminate mortalities (oxytetracycline at 100mg/kg biomass per day, flumequine at 80mg/kg biomass, oxolinic acid at 60mg/kg biomass) and potentiated sulphonamides (trimethoprim + sulfadiazine) at 70mg/kg biomass per day.

However, the disease often reappears in about 2-3 weeks post a seemingly successful therapy.

Thankyou