ACTUAL INFECTIOUS DISEASES IN BULGARIAN PIG INDUSTRY

At the mo ment the most im por tant dis eases for Bul gar ian pig in dus try are clas si cal swine fe ver and Aujeszky’s dis ease in re spect of which we are obliged to meet the re quire ments of the Eu ro pean Un ion (EU) as well as Por cine re pro duc tive and re spi ra tory syn drome and Por cine circovirus type 2, which cause big losses on pig farms. Ac cord ing to the ex perts on pig dis eases we are now in the era of multifactorial dis eases. The emer gence of por cine re pro duc tive and re spi ra tory syn drome (PRRS) and por cine cyrcovirus type 2 (PCV2) in the last 15 years also lead to al ter ation of the pig pa thol ogy and in creased the im por tance of multifactor dis eases. Also, the dis eases im por tant for pig pro duc tion in Bul garia are the dis eases: por cine par vovi rus (PPV), swine influenca vi rus (SIV), Mycoplasma hyopneumonia (M hyo) and Actino bacillus pleuropneumoniae (APP), the in fec tions that of ten joined with above men tioned caus ative agents.


INTRODUCTION
Bul gar ian pig in dus try has some fea tures which in flu ence the in fec tious dis eases. Since 1990 the num ber of farms and pigs has been con sid er ably re duced, and the tendency of de clin ing in pig in dus try is still con tin u ing. Yet, the larg est num ber of pigs is raised on large farms, what con trib utes the oc cur rence of many infectious diseases. Be sides re duced pig pro duc tion, the fol low ing fac tors in flu ence on the oc cur rence of in fec tive dis ease: • breed ing farms are re newed pe ri od i cally by sows and boars, pur chased from other farms, which cre ates con di tions for per sist ing of in fec tious agents; • the im port of an i mals is usu ally done from two or more sources, which en hances the risk of pen e tra tion of the in fec tion; • on some farms the an i mals are reared in the open air, which cre ates a pos si bil ity for con tact with birds and wan der ing an i mals; • in all the farms con tin u ous far row ing is go ing on, which con stantly pro vides suscep ti ble an i mals on the farm; • on all the farms a closed cir cle of per for mance is go ing on and the fatteners serve as a res er voir of per sist ing in fec tions; • boars are reared on farms. On some farms nat u ral in sem i na tion (mat ing) is carried out and boars play an im por tant role in spread ing of in fec tions; • "all in -all out" man age ment is of ten ne glected; • there are pigs reared in back yards; • there is a pop u la tion of East Bal kan bread pigs, reared on pas tures; • the ex is tence of a pop u la tion of wild boars.
Clas si cal swine fe ver (CSF) has been a con stant prob lem in the past with pe ri od ical epi zo ot ics that lasted for sev eral years each. The mass vac ci na tion was an im portant mea sure for lim it ing the losses. Af ter 2002 there is a con stant ten dency of de creas ing the out breaks in do mes tic pigs, ex clud ing 2006 when 3 new out breaks appeared. The last out break in wild boars took place in 2004 and 2005. The out breaks in do mes tic pigs were recovered by "stamp ing out". Ta ble 2: Epizootiological state of Bul gar ian pig in dus try in re spect to CSF (Kamenov, 2009 From Jan u ary 1, 2007 the vac ci na tion of do mes tic pigs is for bid den. In 2005 started the Pro gram for Con trol and Erad i ca tion of CSF, ap proved by EU, which includes (Kamenov, 2009): • ac tive sur veil lance of pig hold ings aimed to as early as pos si ble de tec tion of CSF clin i cal symp toms; • pas sive sur veil lance by in ves ti ga tion of blood sam ples for an ti bod ies; • three vac ci na tion cam paigns of wild boars with two vac ci na tions, each in 40 km zone, along the west ern and north ern border; • con trol of the wild boars by in ves ti ga tion of tis sue sam ples for vi rus and blood sam ples for vac cine -in duced an ti bod ies.

Aujeszky's dis ease (AD)
is a ba sic prob lem for Bul gar ian pig in dus try as af ter stopping the vac ci na tion against CSF it re mains the most im por tant ob sta cle for ex port of pigs in EU. The re sults of virological in ves ti ga tions (vi rus iso la tion in tis sue cul ture), per formed in Na tional Di ag nos tic and Re search Vet er i nary In sti tute (NDRVMI), dur ing the re cent 11 years, show that dur ing all the years AD out breaks have appeared: 62.26% of in ves ti gated an i mals were pos i tive. The big gest num ber in ves tigated (29) and pos i tive (72.41%) were amongst the suck ing pig lets, which is the proof that the vi rus per sists amongst the sows. The con fir ma tion of this state ment is the fact that both foe tuses in ves ti gated were pos i tive. All the in ves ti gated dogs dur ing this period were pos i tive which shows that apart from clin i cal man i fes ta tion AD main tains it self in sows as a la tent in fec tion and the vi rus ex ists in the organs and meat in clinically healthy, in many occasions vaccinated animals ( In the pre vi ous pe riod AD was proved by virological in ves ti ga tion in sheep and cat tle, which shows that AD vi rus in in fected pigs pres ents a con stant threat for other an i mal species.
Al though lit tle, the above men tioned virological in ves ti ga tions are not in the frame of mon i tor ing pro gram, but on oc ca sion of dis ease sus pi cion. In many of the cases of sus pi cion no sam ples were sent for in ves ti ga tion and that is why the dis ease was not registered.
Serological screen ing was also not per formed, but the im ported an i mals were prelim i nary in ves ti gated, but the re sults were not sig nif i cant. The in ves ti ga tion, performed 10 years ago on 20 blood sam ples from each of 14 in dus trial farms, show that more than 42% of the farms and more than 34% of the an i mals were in fected. Al most all the farms and most of the an i mals were pos i tive, which is a proof of vac ci na tion (Motovski et al,1999). Be cause of a small num ber of in ves ti gated an i mals it is not possi ble to say that the other farms were not in fected. As a re sult of many year vac ci nation and sharp de crease of an i mals on the farms, it is pos si ble that some of them got free from the virulent virus.
The Na tional Pro gram for AD Erad i ca tion in cludes in ten sive vac ci na tion with gE -neg a tive and TK -neg a tive high -ti ter adjuvanted vac cines, which al low dis tinguish ing the vac ci nated from in fected an i mals and cre ate strong im mu nity which lim its the vi rus spread. The dis close of AD in fected farms would be per formed by com ple men tary (gE) ELISA, which dis tin guishes vac ci nated from in fected an i mals. Re cov er ing of the in fected farms would be ful filled by grad ual slaugh ter of the infected an i mals and re plac ing them by AD free ones. The coun try will be con sid ered AD free two years af ter the last case of AD. The re cov ered farms will be con trolled yearly by se ro logic in ves ti ga tion. The National program was presented to EU for approval and financing.
Por cine re pro duc tive and re spi ra tory syn drome (PRRS). Yordanov and Chenchev (2000) found an ti bod ies on farms with re pro duc tive dis or ders and re spi ra -tory dis eases. In the fol low ing years this in fec tion took a wide spread and caused great eco nom i cal losses (Motovski, 2001). Most of ten the first sig nal for pen e tra tion of the dis ease into the farm were abor tions ir re spec tive the an ti bi otic treat ment against leptospirosis, which in other cases are ef fec tive. Pre ma ture far row ing (be fore 112 th day of preg nancy), still born and in creased mor tal ity in pigs be fore wean ing were dom i nat ing symp toms in the in fected farms. Re spi ra tory dis eases in weaned pigs were com mon symp toms of this in fec tion. In some farms we ob served re pro duc tive dis or ders only, in oth ers re spi ra tory dis eases in grow ers and on the thirds -sud den death in fatteners. The clin i cal symp toms vary very much in se ver ity on dif fer ent farms de pend ing on the dif fer ence of ex ist ing con di tions -stress, con cur rent in fections, en vi ron ment and prob a bly the vir u lence of the field strain of PRRS vi rus (Motovski, 2004). On many farms we ob served pe ri od i cal ex ac er ba tion of the disease, which shows that the herds were not equal in immunological respect (Benfield et al., 1997).
On the base of immunosuppression, caused by PRRS vi rus (Benfield et al., 1997;Thacker et al., 1999) we ob served ex ac er ba tion of the per sist ing in fec tions on the farms in clud ing such ones that did n't pro duce dis ease in the past. As an ex am ple of this is con sid er able in crease of the se ver ity of enzootic pneu mo nia in grow ers and finish ers and the in crease of clin i cal cases of Str. suis men in gi tis. In a case of acute running of PRRS we ob served ex ac er ba tion of AD with high mor tal ity in sucklers. On a large farm we ob served ex ac er ba tion of por cine par vovi rus with a lot of mum mies and low fer til ity. Re gard less to vac ci na tion, leptospirosis emerged on farms where no clin i cal man i fes ta tion was ear lier ob served. Con trary to some state ments we did n't observe self recovery of PRRS infected farms (Motovski, 2004).
An in ac ti vated (Progressis, Merial) and live vac cine with Eu ro pean strain (Porcilis PRRS, Intervet) were ex am ined. The vac ci na tion with the live vac cine proved safe and ef fec tive -the in crease of fer til ity (P<F2550.02), de crease of re turns and abor tions (P<F2550.001) and the in crease of ex tra ac quired pig lets, which ex ceeded the price of the vac cine (Ta ble 4). Now most of the farms vac ci nate sows with the live vac cine every 3 or 4 months and some of them be fore or af ter wean ing.   PCV2 took a wide spread and af fected all the pig farms and most of the an i mals on them -in 60% to 96% (av er age 75.76%) of sows and pigs on ten in ves ti gated farms an ti bod ies were found (Ta ble 6). The spread of PCV2 in dif fer ent age groups is displayed in Ta ble 7.
Ta ble 6: Prev a lence of PCV2 in in dus trial pig farms  From the ta ble it can be seen that all the age groups were af fected. The pig lets acquired colostral im mu nity, which faded away af ter 18 weeks of age and then the pigs be came sus cep ti ble. Some of the gilts were neg a tive, but they sur vived in fec tion again. Ex cept the in dus trial pig farms now PCV2 is wide spread in back yards and among East Bal kan pigs and wild boars (ta ble 8) ). Ta ble 8: Re sults from in ves ti ga tion ac cord ing to cat e go ries and re gions  On all the in ves ti gated farms we ob served symp toms of PMWS: pro gres sive loss of weight, dif fi cult breath ing, ob vi ous en large ment of in gui nal lymph nodes, di ar rhoea, pale ness and jaun dice. The sick an i mals did n't re act to the treat ment. Dead an i mals showed en large ment of the mesenterial, bron chial and in gui nal lymph nodes, which of ten were red dened, and en large ment of lungs septa (in ter sti tial pneu mo nia) was no ticed. Pigs af fected with PDNS had red to pur ple skin spots pre lim i nary on back of the hams and per i neum which tended to fuse. Such pigs showed an orexia and re luctance to move. The leasons af ter death was lymphadenopathy, en larged kid neys with petehia and multi-col oured lungs, some times with pu ru lent pneu mo nia.
Our ex pe ri ence shows that we can limit the losses of PCV2 by strict ap pli ca tion of gen eral pro phy lac tic mea sures and main tain the herd im mu nity against the ex ist ing dis eases by vac ci na tion, on the first place against PRRS and Mycoplasma hyopneumoniae (M. hyo). In Bul garia an in ac ti vated vac cine for sows (Circovac, Merial) has been reg is tered and also two live sub unit vac cines for pigs Ingelvac Circoflex (Boehringer) and Porcilis PCV (Intervet). Some farms ex am ined the in ac tivated vac cine for sows but were not sat is fied with the re sults. The first re sults from a live vac cine for pigs are encouraging (Table 9). The as so ci ated in fec tions are char ac ter is tic for Bul gar ian pig in dus try as well. By com plex in ves ti ga tions of 13 in dus trial farms we es tab lished that in all of them per sist PCV2, por cine par vovi rus (PPV), in flu enza vi rus (SIV), M. hyo and Actinobacillus pleuropneumoniae (APP), in 70% of them PRRS and in 60% -AD. On 3 pig farms all the 7 in ves ti gated in fec tious agents are pres ent, on 2 they are 6, on 5 -5 and on 3 -4 agents (Ta ble 10). In in ves ti ga tion of 177 pigs on 9 in dus trial pig farms we found that all of them were af fected by AD, M. hyo and APP, but on 5 of them PRRS and SIV exist. The high est per cent of se ro pos i tive and the most farms and an i mals with seroconversion was es tab lished in re spect to APP and AD (Ta ble 11). We de tected as so ci ated in fec tions in pigs in back yards, East Bal kan breed and wild boars as well ). In all the in ves ti gated re gions we found an i mals in back yards with PCV2 an ti bod ies. In Russe re gion pos i tive were half of the in ves tigated an i mals and in Razgrad re gion 90%, but in all the rest re gions all the in ves tigated an i mals were pos i tive. In all of the four in ves ti gated re gions we found pos i tive on SIV an ti bod ies and the dif fer ence be tween them was con sid er able. In 3 re gions there were an i mals with AD an ti bod ies with big dif fer ence be tween the re gions. In each of the three in ves ti gated re gions there were East Bal kan pigs with an ti bod ies against three vi ruses and the dif fer ence be tween the re gions was small. A part of the wild boar pop u la tion in both in ves ti gated re gions had PCV2 an ti bod ies and SIV an tibod ies, on one of them AD an ti bod ies were pres ent as well. In all three cat e go ries of pigs the per cent of se ro pos i tive an i mals was the high est for PCV2 and the low est for AD (Ta ble 12).
Ta ble 12: Re sults from in ves ti ga tion of dif fer ent cat e go ries of pigs and dif fer ent regions  All the in ves ti gated sows and the ma jor ity of the pigs of all age groups in an in dustrial pig farm had an ti bod ies against three vi ruses. The most pos i tive an i mals for PCV2 and SIV an ti bod ies were in fin ish ers, but for AD an ti bod ies -in sucklers (Ta ble 13). The re sults from se ro logic in ves ti ga tions are con firmed by virologic in ves ti gations (Ta ble 14) (Dimitrova et al., 2009).
Ta ble: 13. Re sults from serological in ves ti ga tion (Dimitrova et al., 2009).  4. PRRS be came wide spread af ter 2000 and in duced big losses due to re pro duc tive dis or ders and re spi ra tory dis eases. The vac ci na tion de creases eco nom i cal losses and the live vac cine with Eu ro pean strain is safe and more effective. 5. PCV2 in fected Bul gar ian pig in dus try in the re cent years and spread among domes tic pigs in the in dus trial farms and back yards, East Bal kan pigs and wild boars. It in duces PMWS and PDNS and immunosuppression as well. The vac cina tion of pigs is better than the vac ci na tion of sows. 6. The as so ci ated in fec tions are char ac ter is tic for Bul gar ian pig in dus try as well and in clude as so ci a tion of two or more patho gens: PCV2, PRRS, AD, SIV, M. hyo, APP and PPV. The as so ci ated in fec tions af fect not only the in dus trial farms, but also back yards, East Bal kan pigs and wild boars.