Bull Vet Inst Pulawy 50, 293-297, 2006 STUDY ON THE CONTROL OF VIRAL HAEMORRHAGIC SEPTICAEMIA (VHS) IN POLAND JERZY ANTYCHOWICZ, WITOLD MAZUR2, MICHAŁ REICHERT1, KRYSTYNA PASZOWSKA2 AND MAREK MATRAS Department of Fish Diseases, 1 Department of Pathology, National Veterinary Research Institute, 24-100 Pulawy, Poland 2 Regional Veterinary Inspectorate in Szczecin, Regional Veterinary Laboratory, 75 – 816 Koszalin, Poland e-mail: email@example.com Received for publication May 05, 2006. Abstract Inspectorate in Szczecin, experimental programme of controlling this disease in one chosen river catchment. In 2000 the Department of Fish Diseases of the National Veterinary Research Institute started monitoring the frequency of the presence of viral haemorrhagic septicaemia Material and Methods (VHS) virus in 140 Polish salmonid farms which makes about 70% of all salmonid farms in the country. Special attention was paid to 19 farms situated in A river catchment (river name In 2000 the Department of Fish Diseases of the is coded) and in these farms we started in 1999 the realization National Veterinary Research Institute started examining of the first in Poland experimental VHS control programme. the frequency of VHS virus prevalence in 140 Polish The routine monitoring performed in other 121 farms salmonid farms which makes about 70% of all salmonid (independently of the farms situated in A river) gave farms in the country. encouraging results i.e. resulted in gradually decrease in the Special attention was payed to 19 farms prevalence of VHS cases in Poland. These results have shown situated in A river catchment (river name is coded) and that the simple monitoring connected with immediate in these farms in which the realization of the first in eradication could decrease the prevalence of VHS virus but not Poland experimental VHS control programme has begun in such an extent as might have been achieved by applying the established programme of VHS control in which all fish farms already in 1999. All fish farmers, which were users of A located in certain river catchment participate in its realization. river and its tributaries, regional fish disease specialist and the head of the Fish Disease Department of the Key words: fish, viral haemorrhagic National Veterinary Research Institute accepted the septicaemia, disease control. principles of the programme realization based on the EU Directives and eradication methods which had been applied in Denmark since 1965 (9, 10). Viral haemorrhagic septicaemia (VHS) is the The particular hatcheries supplied with well most serious disease of farmed rainbow trout but affects water were appointed as the source of fishes for also some other inland and marine fish species. The restocking the ponds after eradication. One isolated farm disease is widespread in the world and causes significant (number 1, Table 1) situated as the last one near the production losses and for that reason is listed in OIE outlet of the A river, and supplied with water from a Aquatic Animal Health Codes (8) and in EU Directives small tributary was chosen as a place in which quick (6, 7). fattening of fish survivors of the VHS infection took Many countries run a control programme on place. VHS and as result some of them achieved the status Twice a year, since 1999 up to now, in spring officially free of this disease. Officially there are no and autumn, at the water temperature below 15°C, VHS free farms or river catchments in Poland though regional fish disease specialist surveyed all farms in A the disease cases are decreasing (1, 5). Therefore the river catchment and selected 140 – 150 fryes and Fish Disease Department of the National Veterinary fingerlings or 30 two year old fish from each farm for Research Institute started VHS monitoring in the whole virological investigations. Sampled fishes were country and, independently, together with the Veterinary euthanized and sent to the Fish Disease Department in containers cooled inside to 4 - 8°C. 294 Table 1 VHS prevalence in rainbow trout farms in A river catchment in 1999 – 2005 Farm 1999 2000 2001 2002 2003 2004 2005 1* VHS - VHS VHS VHS - - 2 VHS - - - VHS - VHS 3 - - - - VHS - - 4 VHS - - - - - - 5 - - - - - - - 6 - - VHS - - - - 7 - - - - - - - 8 - - - - - - - 9 - - - - - - - 10 - - - - - - - 11 VHS - VHS - VHS VHS - 12 VHS - VHS - - - - 13 VHS - VHS - VHS - - 14 - - - - - - - 15 - - - - - - - 16 - - - - - - - 17 - - VHS - - - - 18 - - - - - - - 19 - - VHS - - - - * Farm used for quick fatening of VHS survivors. In the laboratory the fish internal organs were Results pooled, homogenized and subsequently supernatants were used for the inoculation of the BF – 2 and RTG – 2 Cases of VHS virus infections accompanied cell line cultures. VHS virus was identified using ELISA with clinical symptoms were detected only in rainbow and RT-PCR methods. Besides regular monitoring in trout. In some cases the haemorrhagic changes were also each case of VHS suspicion, 30 fish with clinical observed in rainbow trouts after smoking. Numbers of symptoms were sampled and immediately examined in VHS virus infected rainbow trout farms in A river regional laboratory using quick direct ELISA method, catchment in 1999 – 2005 are presented in Fig. 1. VHS then the samples were sent to the Fish Disease prevalence in rainbow trout farms in A river catchment Department of the National Veterinary Research in 1999 – 2005 is shown in Table 1 and the results of Institute for confirmation. monitoring of VHS in 121 farms in Poland are depicted Occasionally the smoked rainbow trouts were in Fig. 2. Typical, most often observed symptoms of checked on the eventual symptoms changes VHS in live rainbow trouts are illustrated in Figs 3, 4, 5 characteristic of viral diseases. and in smoked fish in Fig. 6. The fish farms were being closed each time when suspicion of the VHS virus presence had been noted i.e. when clinical signs in fish or cytopathic effect Discussion in cell culture had appeared. The eradication ensued if the VHS virus presence was confirmed. Up to this time in Poland clinical symptoms of Since 2000, independently of realization of the VHS has been observed only in rainbow trout and this VHS control programme in A river catchment, also the phenomenon confirmed that this fish is most susceptible routine monitoring has started in other 121 farms. In this to VHS virus infection. In one case the presence of the case the samples of 30 fish were being collected twice a virus was found in symptomless brook trout kept in the year and sent to above mentioned Fish Disease ponds neighbouring those in which VHS had appeared Department for virological examinations. Furthermore, in rainbow trout. It suggests that the brook trout could be in each case of VHS suspicion 30 fish with clinical infected with the virus from rainbow trout and could be symptoms were sampled and examined virologically. In a potential carrier of VHS virus later. the majority of cases samples consisted of rainbow trout. During 6 years of this monitoring brook trout was sent from 12 farms and brown trout from 6 farms only. 295 10 9 number of VHS infected farms 8 7 6 5 4 3 2 1 0 year year 1999 2000 2001 2002 2003 2004 2005 Fig. 1. Numbers of VHS infected rainbow trout farms in A river catchment in 1999 – 2005. 16 14 number of positive farms 12 10 8 6 4 2 0 1 year 2000 2 2001 3 2002 4 2003 5 2004 6 2005 year Fig. 2. The results of monitoring of VHS in 121 salmonid farms in Poland excluding farms situated in A river catchment (National Veterinary Research Institute data). Fig. 3. Haemorhages in the base of breast fins in VHS Fig. 4. Haemorhages in rump muscles in VHS affected affected rainbow trout. rainbow trout. 296 identified in two consecutive years (Table 1). It was found that the uncertified fishes had been used for restocking these farms, contrary to the previously made decisions that fishes for restocking must be delivered from virus free farms fed from brooks or wells. According to regional fish disease specialist who was supervising the realization of the programme, the disinfections were being performed adequately but in farms 11, 12, 13 the majority of VHS cases appeared in short time after introduction of uncertified fishes which were apparently harboured by the virus. This was obviously the cause of VHS recurrence. In three other cases the relationship between the introduction of carps (as additional fish) to salmonid farms and VHS appearance was suspected. The facilities Fig. 5. Haemorhages in visceral fat in VHS affected used for carp transportations were utilized previously for rainbow trout. rainbow trout delivery so it is quite possible that contaminated water and lack of proper disinfection were responsible for the case of VHS occurrence. The random examinations of free living rainbow trout in A river did not show the presence of VHS virus in these fishes (unpublished data) so they possibly could not be the source of infections. The routine monitoring performed in other 121 farms (independently of the farms situated in A river) gave encouraging results i.e. a gradual decrease in VHS cases in Poland was observed (Fig. 3). The number of infected farms in the consecutive years of the monitoring realization (2000 – 2005) was the following 13, 15, 13, 8, 4 and 4. These results have shown that the simple monitoring connected with immediate eradication could decrease the prevalence of VHS virus but not in such an Fig. 6. Haemorhages marks in smoked rainbow trout left extent as might have been achieved by applying the after haemorhages which had been developed established programme of VHS control in which all fish during VHS infection. farms located in certain river catchment participate in its realization. The reason of a dramatic decrease in VHS cases in Poland was probably the change in sampling In the course of VHS in farmed rainbow trout procedures that has taken place since the half of 2003. high morbidity and mortality rates were observed which The results of this study showed, however, that one of usually exceeded 50% of affected trout population. The the main factor which positively influence VHS statistic direct economic impact of the disease was linked to its in Poland is the decrease in VHS cases in river A morbidity, mortality and degraded quality of fish meat. catchment owing to the realization of the regular VHS For instance, the petechiae which are caused by the virus control programme. infection in live fishes can be also observed in smoked The results we have achieved during ones (Fig. 6). programme realization in A river catchment were quite In farms which purchased mainly eyed ova for encouraging considering that for many years this region the first stage of production (farms 3, 4, 5, 7, 9, 15, 16, was the most intensively affected one with VHS in 19, Table 1) the prevalence of VHS cases was much Poland. The lack of quite satisfactory results i.e. lower than in farms which were getting only fryes or numerous VHS recurrence cases was caused by some fingerlings for quick fattening (farms 2, 6, 8, 10, 11, 12, farmers, who did not apply to the rules and stocked their 13, 14, 17, 18). In the first group during 7 year pond with uncertified (cheap) fishes. Water from not observation only 3 VHS cases were recorded i.e. adequately disinfected transport facilities being the approximately 0.4 case per one farm whereas in the source of infection could also cause VHS recurrence. second group 14 VHS cases have appeared that makes The positive and negative experience which 1.4 case per one farm. have been gained by the participants of this first During the first five years of programme experimental programme could be applied in the near realization in some farms (farms 2, 11, 12 and 13) the future for the eradication of the disease in other Polish recurrence cases of VHS were observed every second river catchments. The results of this programme year after eradications had been completed and in one convinced the fish breeders and field veterinarians that farm (farm 11) additional two cases of VHS were eradication of VHS in Polish salmonid farms could be 297 possible, however, in the long run, provided that during VHS, IHN w dorzeczu rzeki Grabowa. Problemy realization of such a programme all farmers will apply to pstrągarstwa polskiego. Olsztyn 2002, pp. 97-105. the established rules based on the principles presented in 4. Antychowicz J., Pękala A.: Viral haemorrhagic EU Directives and also those which take into account septicaemia (VHS) and infectious haematopoietic necrosis (IHN) of fish in Poland and European countries. specificity of particular river catchments. Medycyna Wet 2002, 58, 341-343. 5. 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