Outbreaks due to a massive and short term intake of metacercariae are usually the great concern in areas with high rainfall and anything favoring for wetland development combined with a lack of flukes control measures [13, 14]. Detection of immature flukes in liver sample from 50 sheep out of 50 (100%) and 82% (41/50) Clostridium positive clearly indicates that the outbreak was due to acute fasciolosis predisposed Clostridia infection. This is the first outbreak of an acute fasciolosis predisposed Clostridia infection reported in Ethiopia. However, Fasciolosis with a prevalence of ranging 11.5% -87% is one of the most important parasitic diseases of ruminants in various parts of Ethiopia [15, 16, 17, 18, 19, 20].
The outbreak occurred on a specific grazing land located in an area endemic for fasciolosis in Tumbio village of Korem town, ofla District . (Topography of the specific grazing land is flat with wetlands. The water is pumped from different drainages of Korem town and stay for almost one month. The grazing system of the village for this specific grazing land was by fencing for all most three months the grazing land was opened for oxen only for two months then the grazing land was opened for all livestock population of the village. This provides massive development of metacercaria because of the survival metacercaria before fencing and egg shaded from oxen . Altitude of Korem town is 2539 meters above sea level with temperature ranges of 44°F to 78°F. There was high rainfall from June to the end of August in Korem. All this geographical and environmental characteristics of the area where this outbreak occurred were enhancing the epidemiology of fascioliasis [23, 24, 25, 26].
The clinical features of acute fasciolosis observed in this outbreak were in agreement with previous report [27, 28, 14, 29].
Based on data of cross-sectional and longitudinal observation from Korem veterinarian and livestock producers of Tumbio village of this study, a total of 1966 outbreaks were identified using the case definition. The attack rate and case fatality rate for this outbreak was 94.25% and 95.6% respectively, which was much higher than acute fasciolosis reported in various part of the world; attack rate and case fatality of 3 to 66.7% and 3 to 50% in southern Brazil ; case fatality of 18.3 % on a livestock farm near Minchanabad in Bhawalnagar district ; mortality rates range from 15–20% ; 10% sudden death of flock . The high attack and case fatality rate in acute fasciolosis of this outbreak might be attributed to the fact that geographical and environmental factories provides massive development of metacercaria then the gazing system of the village causes the sheep to consume this massive metacercaria in short period. Additionally, due to absences of clostridial vaccinations practices in the district this acute syndrome was complicated with concurrent Clostridium novyi. Furthermore, this might be due to treatment for fasciolosis in district have been applied randomly and independently in the local herds, without any attempt to adopt an integrated parasite control program for the district including without following any technical recommendation such as correct dosage, frequency, application rout, etc.
Even if, at the end of our results during longitudinal observation indicates that except the young suckling sheep which did not start grazing all sheep group were attacked by the outbreak, the cross-sectional observation showed female, pregnant and lactating sheep were first become ill and died. This could be explained by the fact that, females are more prone to parasitism during pregnancy and peri-parturient period, because this causes stress and decreased immune status .
The post-mortem examination was revealed two important points. The first point was the enlarged, rounded edges and irregular capsular surface of liver observed in all 50 slaughtered sheep, which is in agreement with the report of [34, 32] study for acute fasciolosis. The second was varying occurrence of multiple gastrointestinal helminthes between slaughtered sheep. Mixed parasitic infections were similarly reported [35, 36].
Parasitological fecal egg and immature fluke examination were done. Based on this parasitological fecal egg examination finding of this study were mixed parasitic infection with predominant helminth egg of Strongyles followed by Paramphistomum. This result was in agreement with previous report in Ethiopia high land sheep [37, 38, 39, 40]. However, no massive deaths were reported in those previous reports. Interestingly, in this study immature fluke from live samples were recovered in all (50/50) of the examined samples. This magnifies the presence of immature fluke could potentially contribute for this outbreak. Similarly, immature fluke were recovered in previous acute fasciolosis outbreaks reports even if there were negative for fasciolosis egg [41, 42, 34, 32].
Histopathologically, liver with multifocal necrosis, fibrocystic proliferations in areas where hepatocytes were died and removed, multifocal and diffused infiltrations of inflammatory cells were observed in the present study. This finding is in consistent with other reports of pathological changes caused by acute fasciolosis [43, 30].
Out of 50 microbiological examined sheep for Clostridium complication 82% (41/50) were identified as Clostridium positive. Clostridium was also isolated by [44, 45, 46] from tissue necrosis and local anaerobiosis of liver caused by migration of immature forms of flukes mainly fasciolosis. Toxemia and profound hypoproteinaemia produced by clostrdial organisms causes liver damage, treatment failure and follows by quickly death (https://www.merckvetmanual.com). Similarly, in this finding no cure was observed after all active case were treated with procaine penicillin, triclabendazole and multivitamin. So it can be concluded that the high case fatality rate and treatment failure of this outbreak caused by acute fasciolosis was due to complication of Clostridium infection.