The Babylon River's common carp (Cyprinus carpio) gills were used for the histopathological examination and PCR detection of Koi herpesvirus disease (KHVD)

The first outbreak of koi herpesvirus in Iraq occurred in Babylon Province in the floating cages in the Euphrates River from the Musayyib thermal electric power station to the Al-Hindiya Dam. Fish were suffering from gills rot that did not respond to treatment and lesions and ulcers on the fish's body. The fatalities reached 80%. was water temperature 24°C, pH 6.85, Salinity 760 ppt. So the present study aims to highlight the pathological changes in gills after the Koi herpes virus infection in Babylon Province. The study started after the detection of (KHV) by polymerase chain reaction ( PCR) from the suspected samples (30 ) for the detection of virus nucleic acid. Also, study the water characterization during the periods of outbreaks. The gills specimen was collected from the positive cases for gross and histopathological examination. The result showed that ten samples were positive for (KHV) infection. The gross and histopathological examination results showed severe congestion with necrotic foci and sloughing of secondary lamella with increased mucus secretion. In addition, necrosis in the primary lamellae, Edam and inflammatory cells infiltration with hyperplasia of the secondary lamellae with the presence of intranuclear inclusion body in all exanimated slides.
 
Keywords: Koi Herpes; Cyprinus Carpio; Euphrates River; KHV; secondary lamellae; floating cages