9 Recent Experience of Field Vaccination Trials

8/13/2019 9 Recent Experience of Field Vaccination Trials

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Recent Experience of Field Vaccination TrialsAgainst Vibriosis in Rainbow Trout Salmo gairdneri)T. HASTEIN t F. HALLINGSTAD2 , T. REFSTe and S.O. ROALD)

ntroductionVibriosis is one of the most serious infectious fish diseases occurring in sea water, andthe disease is often the major problem in the rearing of salmonid fish, causing considerable economic losses in the marine fish farming industry. These losses are due toincreased mortality, reduced growth, and costs of medical treatment.

Since medical treatment is expensive as well as hazardous to the ecosystem, worldwide efforts have been made to find other means of protection against fish diseases,such as change in management procedures, genetic improvements, isolation as well asvaccination programs Harell, 1979; Antipa, 1976; Fijan et aI., 1977; Gunnels et aI.,1976; Christensen, 1977; Hami and Kusuda, 1978).

Vaccines can be applied to fish orally added to the feed, by intraperitoneal injections, by dipping of the fish, or by the shower method. For mass vaccination the dipor shower method would probably be preferable because of the inconsistenciesencountered with the oral method and the increased stress to the fish, and the highcosts connected with the inoculation method Harell, 1979). Hami and Kusuda 1978)claim that the spray method is less stressing to the fish than the dip method.

Vaccination is now the preferred method of vibriosis control among northwestcoast commercial salmon growers. According to Norwegian legislation of fish diseases,fish can only be vaccinated with vaccines approved by the Veterinary Division, Ministryof Agriculture. The purpose of the experiments described here was to compare andevaluate the effectiveness of a commercially available vibrio vaccine and a formalinkilled bacterin prepared at the National Veterinary Institute.

Materials and MethodsFacilitiesThe vaccines were tested in several fish farms. The immunization procedures were performed with the fish in freshwater either in fiberglass tanks or in earthen ponds.

Approximately 14 days post vaccination the fishes were transported to sea-waterfish farms except in the cases when the vaccination was done at the weight stage of 1 g.1 National Veterinary Institute, Oslo, Norway2 Holmane Experimental Fish Farm, Sirevll.g Norway3 Fish Breeding Experimental Station, Sunndals0ra, Norway

W. Ahne (ed.),Fish Diseases

Springer-Verlag Berlin Heidelberg 1980


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54 T. H l.stein et al.FishRainbow trout Salmo gairdnerij were used in the set-up, ranging in average weightfrom 1 to 300 g. These fishes were supplied from various freshwater fish farms duringthe period 1977-1979.VaccinesBacterins were prepared at the National Veterinary Institute from Vibrio anguilliJrum,strain A 20/76, after 48 h growth at 24C on Trypticase soy broth (30 g per literdistilled water). The cells were killed with 0.5 concentrated formaldehyde for 1 hat 37C. The product contained approximately 1010 bacteria/ml. The commerciallyavailable vaccine Hivax from Tavolek Laboratories was used according to the re-commendations of the manufacturer. t was applied either by dipping or by intraperitoneal (IP) injections, while the locally prepared bacterin was used only as IP,injections in doses of 0.5 ml per fish.

For marking and IP immunization Chlorbutol (300 mg/l) was used as anesthetic.

Recording ofMortalitiesIn some of the field trials quite exact recording of mortality was achieved throughoutthe period when the fishes were kept in sea water, while in the commercial fish farmsonly more approximate figures have been obtained.

The death rate in connection with vaccination procedures was negligible and therainbow trout did not seem to suffer much from marking, handling stress, and injection.

ResultsIn one controlled field experiment which lasted for one year 1977-1978) the effectofHivax and the produced bacterin was compared. Throughout the experimental periodthe fish suffered from spontaneous outbreaks of vibriosis. No medical treatment wasgiven. Table 1 shows the mortality figures in each group of fish and the results clearlydemonstrate a significant protection of the vaccinated fish against vibriosis.In another series of controlled field experiments started in the spring of 1979

vaccination programs on different age groups of fish were compared. Table 2 shows nodifference in mortality between fish vaccinated at the 100-g and at the 300-g stages,while fish vaccinated at the weight of 1 g showed the same mortality rate as the controls. The situation became very clear due to natural outbreaks of vibriosis at the endof July, approximately 1 month after transfer to sea water, and in mid-October (Figs.I, 2). The control groups in cages 6 and 8 were left without antibiotic treatment whilethe fish in cage 9 (Hivax, I g) were medicated from 15-20 August and from 13-17 Oc-tober. The medication was effective in reducing mortality rate in cage 9, but the mor-


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Recent Experience of Field Vaccination Trials Against Vibriosis 55Table l Mortality figures in a controlled field experiment 1977 1978

No dead fish fromxperimentalgroups

Number offishes

Average weightwhen vaccinated 31 Oct. 1977 30 Nov 1978 Percent mortality

Controls 1881 75 g 472 25.1Hivax IP 1812 75 g 228 12.6Hivax dip 475 75 g 57 12.5Norwegian IP 1832 75 g 178 9.7Vaccination date: 31 October 1977Transferred to sea water: 11 November 1977Slaughtered: 30 November 1978

Table 2 Mortality figures in a controlled field experiment 1979Experimental groups Number of fishes Average weight

in experiment when vaccinatedHivax dip 900 100 gHivax IP cage 6 900 100 gNorwegian IP 950 100 gControls 900 100 gHivax dip 700 300 gHivax IP cage 7 1200 300 gNorwegian IP 1200 300 gCon tro s cage 8 3100 300gHivax dip cage 9 3366 Vaccinated 1978at 1 g spaceweight whentransferred to

sea water 130 g

Vaccination date: 20 May 1979Transferred to sea water: 5 June 1979

Mortality figures Percent mortalityfrom start to 22 Oct

7 0.782 0.220.11

175 19.442 0.290.427 0.58370 11.94

409 12.15

The fish in cage 9 were treated with oxytetracycline from 15 20 August 1979 and from 13 17 Oc-tober 1979. The other groups were left untreated

tality rate in the nonmedicated groups was also significantly lowered during the sameperiod. Figure 3 shows the cumulative mortality within the various groups from thestart of the experiment until now. The fish in cages 7 and 8 will be slaughtered inNovember 1979 while the fish in cages 6 and 9 will be kept in sea water until Oc-tober - November next year and this set-up might give some information on the lastingeffect of vaccination throughout two summer seasons.

Table 3 shows the results of vaccination in several commercial fish farms. Thefigures show that vaccination seems to be an effective prophylactic treatment al6neor in combination with medication.


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Fig. l. Daily mortality rates of various groups of rainbow trout. Day I means day of transfer to seawater, ___ Control fish 300 g). --- Fish dip-vaccinated in Hivax at the l-g stage. These fisheswere treated with oxytetracycline from 15 20 August and from 12 17 October. 0 Fish vaccinatedat the 100- and 300-g stages with Hivax and our own bacterin .. Sea-water temperature

28

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>- I 6o(; 12E

70oay5 after Sea water exp05ure

Fig. 2. Daily mortality rates in percent in various groups of rainbow trout after transfer to seawater. __ Unvaccinated 300-g control group. 0-0-0 Unvaccinated 100-g control group.--- Fish dip-vaccinated in Hivax at the l-g stage. A ows indicate start and end of antibiotictreatment. 0 Fish Vaccinated IP with Hivax or bacterin at the IOO or 300-g stages .... Sea-watertemperature

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Recent Experience of Field Vaccination Trials Against Vibriosis

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Fig. 3. Cumulative mortality rates in percent in various groups of rainbow trout after transfer tosea water. __ Unvaccinated control group of 300 g. o-()-() Unvaccinated control group of100 g. Fish dip-vaccinated in Hivax at the 1-g stage. rrows indicate start and end ofantibiotic treatment. - .. - .. - Fish vaccinated with Hivax or bacterin at the 100- or 300-g stageby dipping or by IP injections Sea-water temperature

DiscussionThe survival rates are consistent with those experienced by other workers. Sawyer andStrout (1977) compared vaccination with medication in preventing vibriosis in cohosalmon. Both methods caused increased survival rate and growth compared to the controls, and the total mortality rates were 2.9% in the vaccinated fish, 6.7% in the medicated ones, and 23.6% in the controls. Similar protection rates have been found inrainbow trout in vaccination experiments in Norway by H ~ s t e i n et al. (1977), and byEgidius and Andersen (1979).

The last-mentioned authors used a Vibrio anguillarum bacterin prepared by trypsindigestion of the bacteria and a bathing period of 2 h. There was a mortality of 2.5% inthe vaccinated group compared to 54 in the controls on challenge 4 months later.Similar mortality figures were recorded by Gould et al. (1979) when fishes vaccinatedby the immersion method with a bivalent bacterin were challenged. In potency testswith Hivax, the challenge dose caused a mortality rate of more than 90% in the controlgroups and a corresponding 10 in the vaccinated group (Tavolek Technical Report,1978).

Tavolek has also found similar mortality rates in fish dip-vaccinated at the log stageand later challenged. The death rates recorded correspond well with our findings. Evenif fish basically seem to be immunocompetent at the stage of approximately I g,vaccination at this stage does not give a long-lasting immunity. The mortality rate on


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58 T. HRstein et a1.Table 3. Vaccination results of field trials in some commercial fish farms

Average weight Approxi-Fish Number of fish of fish when Vaccination Mortality mate MedicalFarm Vaccinated Nonvaccinated vaccinated period rate mortality % trea tment

13,000 90 g 15 Oct 1977 431 3.3 None-15 Sept.1978

15,000 400-500 80g Autumn 450 2.7 Yes. Due1978-79 to pollu-

tion withsmall,nonvacci-nated fishamong thevaccinatedfish

3,700 80g 1977-78 75 2.03 NoneIV 41,000 12 60g 1977-78 40,000 Approxi- None

229 mately 1in vacci-nated,60% innonvacci-nated

V Brood fish - None NoneVI 9,000 100g Spring 1979 - 0.1 None9,000 100 g Spring 1979 300 3.3 YesVII 2,000 100 g Spring 1979 Yes

6,000 100 g Spring 1979 NoneVIII 100,000 1 g 1978 No records Yesbut vibriosisoccurredIX 15,000 100 g Spring 1979 - 0.33 None20,000 100g 1979 2.5 Yes

challenge seems to be the same as for unvaccinated rainbow trout (Downs, 1979).Since the cost of vaccination increases with increasing size of the fish, some experimentswith vaccination of fish with Hivax at the 5-g stage have been started in 1979. Thesefishes have not yet been exposed to sea water.

However, vaccination of rainbow trout seems so far to give the best results whenlarge fish are vaccinated some few weeks before they are transferred to sea water.

Though medication of rainbow trout against vibriosis offers as good results asvaccination, vaccination should be the future choice of treatment since the risks of development of drug-resistant pathogens and possible drug harm to consumers are avoidedby this method.

What application method to be chosen for vaccination will depend on several factors such as number and size of the fish to be vaccinated and costs of vaccine.


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Recent Experience of Field Vaccination Trials Against Vibriosis 59Additionally, vaccination might be combined with genetic improvements as there

is a significant difference in antibody titers in offspring after different fathersP

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9 Recent Experience of Field Vaccination Trials