Ljubo Barbić, Vladimir Stevanović, Josip Madić
Zavod za mikrobiologiju i zarazne bolesti s klinikom, Veterinarski fakultet Sveučilišta u Zagrebu
E-mail: ljubo.barbic@vef.hr
Ljubo Barbić (Faculty of Veterinary Medicine, University of Zagreb, Croatia)
Virus Zapadnog Nila uzročnik je oboljenja u ljudi i različitih vrsta životinja. Uz primarnog domaćina, ptice, virus sporadično uzrokuje bolest s mogućim smrtnim ishodom u ljudi i konja. U konja se bolest najčešće javlja supklinički, ali se u određenog broja životinja javljaju i različiti klinički oblici. Klinički oblik bolesti u konja očituje se sa simptomima sličnim influenci, a životinje se obično oporave za 7-10 dana. Međutim, u oko 30% oboljelih konja zaraza se očituje encefalomijelitisom, koji u vrlo visokom postotku završava uginućem ili medicinski opravdanom eutanazijom. Konji koji prebole neurološki oblik bolesti uglavnom se u potpunosti oporave za 1-6 mjeseci, dok u 10% životinja ostaju trajne posljedice.
Podaci dobiveni istraživanjem infekcije virusom ZN u konja mogu biti od važnosti za javno zdravstvo. Naime, program kontrole virusa Zapadnog Nila na određenom području provodi se pretraživanjem uginulih ptica, kontrolom vektora, pretraživanjem klinički oboljelih konja i pretraživanjem “sentinel” životinja, a u tu svrhu se najčešće koriste konji i/ili domaća perad. U dosadašnjim istraživanjima dokazano je da se na područjima s visokim postotkom serološki pozitivnih konja (IgG), može očekivati pojava kliničkih oblika u konja i u ljudi. Stoga praćenje aktivnosti virusa Zapadnog Nila u konja kao “sentinel” odnosno „prokazivačkih“ životinja omogućava predviđanje rizičnih područja za pojavu kliničkih oboljenja u ljudi. Prateći pojavu zaraze u ljudi i aktivnost virusa, spoznalo se da njegova aktivnost u ptica, komaraca i akutne infekcije u konja prethode kliničkim slučajevima u ljudi. Iz navedenoga se razabire da program kontrole virusa Zapadnog Nila u životinja daje vrijedne podatke za javno zdravstvo.
Iako je u Hrvatskoj prva prijava slučajeva akutno inficiranih konja i oboljenja ljudi zabilježena ljeti 2012., istraživanja prisutnosti i proširenosti virusa provedena su mnogo ranije. Infekcija virusom Zapadnog Nila u konja u Hrvatskoj prvi put je dokazana pretragom uzoraka seruma iz 2001. i 2002. godine u Istočnoj Slavoniji. Opsežnije istraživanje provedeno je tijekom 2010. godine kada je aktivnost virusa Zapadnog Nila dokazana u 8 županija Hrvatske s najvišom seroprevalencijom u Istočnoj Hrvatskoj, području koje graniči s Mađarskom, Srbijom i Bosnom i Hercegovinom, te u Istri graničnom području prema Italiji. Seroprevalencija po županijama iznosila je od 1,4% do 9,1%, a na razini države 3,5%. Na osnovi navedenih rezultata, 2011. godine, uveden je program kontrole proširenosti virusa Zapadnog Nila na području RH. Obuhvaćeno je osam županija, a aktivnost virusa dokazana je u sedam. Ponovo je najviša seroprevalencija dokazana na području Istočne Slavonije, a ukupna seroprevalencija u pretraživanim županijama iznosila je 3,7%. Program kontrole proširenosti virusa Zapadnog Nila u konja 2012. godine nastavljen je dokazivanjem specifičnih IgM protutijela. Akutne infekcije konja dokazane su u najistočnijem dijelu države u uzorcima uzorkovanim od 20. 7. 2012. do 1. 8. 2012. Oko mjesec dana nakon toga, dokazani su i slučajevi oboljenja ljudi na istom području. Naknadnim pretraživanjem uzoraka na prisutnost IgG protutijela dokazano je da je seroprevalencija u konja u županijama s kliničkim očitovanjem u ljudi bila viša od 7,5% dok je u županijama bez zabilježenih slučajeva bolesti u ljudi bila manja od 3%. Istraživanja provedena tijekom 2012. godine pokazuju da su rezultati kontrole aktivnosti virusa Zapadnog Nila u konja bili indikativni za mjesto i vrijeme pojave kliničkih oboljenja ljudi.
Zaključno, višegodišnji dokaz aktivnosti virusa Zapadnog Nila u konja u najmanje 9 županija RH ukazuju na moguće enzootsko pojavljivanje bolesti. Nadalje, RH je vjerojatno dio značajno većeg enzootskog područja i bolest se najvjerojatnije širi iz dva pravca, s jedne strane iz Srbije i Mađarske te s druge strane iz Italije. Stoga je pojava budućih epidemija bolesti u sljedećim sezonama vrlo izvjesna. Prikazani rezultati istraživanja u konja i klinički slučajevi u ljudi tijekom 2012. godine govore o značenje konja kao “sentinel” životinja. Rezultati istraživanja omogućuju predviđanje mjesta i vremena pojave kliničkih slučajeva u ljudi. Navedeno obvezuje na daljnje provođenje programa kontrole virusa Zapadnog Nila u još većem opsegu.
West Nile virus serosurveillance in horses in Croatia
Ljubo Barbić, Vladimir Stevanović, Josip Madić
Department for Microbiology and Infectious Diseases with Clinic, Faculty of Veterinary Medicine, University of Zagreb
E-mail: ljubo.barbic@vef.hrWest Nile virus (WNV) is well known cause of infection in the different animal species and also humans. Birds are primary hosts but clinical illness with fatal end can also be seen in humans and horses. Most of the infections in the horses are subclinical, but in some portion of infected animals different clinical symptoms can occur. Most common manifestation of WNV infection in horses is influenza like syndrome that is self limiting and full recovery is expected in 7 to 10 days. On the other hand in 30% of clinically diseased horses symptoms of encephalomyelitis predominate and in many cases animals die or they have to be euthanized. Horses that survive neurological form of the disease can fully recover but in 10% of animals permanent disorders persist.
Data obtained in horse population are of outmost importance for public health. Surveillance program in some area is based on examination of the dead or dying birds, the vector control, examination of diseased horses and using of the sentinel animals, usually poultry or horses. Some studies showed that the areas with high prevalence of the IgG positive horses are the areas in which clinical manifestation of WNV infection in the humans and in the horses is expected. Even more, usually evidence of WNV circulation, in terms of increased viral activity in birds, WNV positive mosquito pools and acute infections in horses precede clinical cases in humans. All these data make possible predicting the occurrence of illness in human population. Accordingly, data of surveillance program of WNV circulation in animals gives invaluable data for public health.
Despite that the first cases of acute infected horses and clinical cases in humans were reported in the summer 2012, monitoring of the presence and prevalence of the WNV has been done for some years before. First serological evidences of the WNV infection in horses date from 2001 and 2002 and it was made in sera samples of the horses in Eastern Slavonia. More extensive study was made in the year 2010 when the WNV activity was confirmed in the 8 Croatian counties with the highest seroprevalence in eastern Croatia in the area that lies next to the state borders with Hungary, Serbia and Bosnia and Herzegovina as well as in Istria, county next to Italian border. The seroprevalences, on the county level, were from 1.4% to 9.1% and on the state level it was 3.5%. In the 2011, based on the results from previous study, official surveillance system on a state level has been established. In 2011 in 8 of Croatian counties surveillance was made and in the 7 of them the WNV activity was confirmed. Again, like in previous year, the highest seroprevalence was in Eastern Slavonia with average value of 3.7% in all counties included. Surveillance program has been continued in 2012 with focus on testing horse sera samples for the WNV specific IgM antibodies as a proof of acute infections. Confirmation of acute WNV infections in horses was made in the easternmost part of country, in sera sampled between 20th of July and 1st of August. In a month, from first confirmation of acute infection in horses, first clinical cases in humans were confirmed in same area as well. Testing of the sera samples for the presence of IgG specific antibodies that had been done afterwards, seroprevalences in counties with human cases were uniformly higher than 7.5% and in the rest of counties had been less than 3%. Results of surveillance program in 2012 shoved that it had been possible to make the good prediction of the time and the place of occurrence of human cases.
In the conclusion, evidence of the WNV activity for many years in at least 9 counties, indicates possibility of WNV endemisation in Croatia. There is high possibility that Republic of Croatia is the part of the larger endemic area and the spreading of WNV is probably coming from two directions, Serbia and Hungary on the one side and Italy on the other. Possible endemisation make occurrence of new epidemics in future years almost inevitable. All the showed results of the studies in horses and clinical cases in humans in 2012 highlight the importance of the horses as sentinel animals that could give us possibility to predict place and the timing of occurrence of human cases. All together should result in the extending of the surveillance system in the coming years because of the importance for veterinary medicine and even more because the obtaining invaluable information for public health.