- Test results from international laboratories confirm that the death of millions of farmed carp in Iraq in late 2018 was caused by fish disease, not pollution.
- The carp suffered from the Koi Herpes Virus (KHV), a lethal disease known to cause almost 100 percent mortality rates in carps.
- Based on these results, we can therefore rule out that chemical contamination played a role in the fish kill, which should reassure the public that the farmed carp is safe to eat.
On 26 October 2018, a major fish kill episode that wiped out millions of mostly caged farmed carp in Iraq’s central Euphrates region sent the country into major panic. Fear spread that the fish kill was caused by a mysterious pollution that could also poison people, whilst fish farmers agonized over their losses as the source of their livelihoods abruptly vanished.
Deeming the fish kill a national security issue, Iraq’s newly appointed Prime Minister, Dr. Adel Abdul Mahdi, immediately assembled a crisis team led by the Ministry of Health and Environment and the Ministry of Agriculture to investigate its causes and take appropriate remedial measures.
“The scale of the fish kill was so huge, we had excavators working for four days clearing the fish from the river,” affirmed Dr. Ala Alwan, Iraq’s Minister of Health and Environment, who personally inspected the situation on the ground once news of the incident broke out. “We also used oil spill booms to contain and prevent the fish from drifting downstream, especially as many fish farmers rashly dumped the dead carp into the Euphrates River,” he added.
Faced with this unprecedented massive fish mortality, the Iraqi Government decided to request emergency technical assistance from the World Health Organization (WHO), the Food and Agriculture Organization (FAO) and UN Environment to help determine the cause of the sudden die off.
Fish and environmental samples were collected by the Ministry of Health and Environment based on UN Environment’s advice from the epicentre of the fish kill incident near Al-Musayab, Babel governorate, approximately 70 kilometres south of Baghdad. Since 2011, this area had become a thriving hub for Iraq’s growing fish farming industry where a rapid expansion in the use of floating river cages to grow common carp (Cyprinus carpio) became established. At the same time, “the high density of fish cages almost back-to-back for kilometres, coupled with extreme overstocking, contravened national regulations,” cautioned Minister Alwan.
UN Environment, WHO and FAO rapidly organized for the fish, water, sediment and fish feed samples to be shipped to internationally-accredited laboratories. Comprehensive chemical and microbiological tests were carried out by three different laboratories, including in Switzerland, Jordan and Italy.
For all the samples taken by the Ministry of Health and Environment, test results showed no significant contamination from heavy metals, hydrocarbons or pesticides. “Unlike water, which only gives a snapshot of environmental conditions at a specific point in time, sediment acts as a storage reservoir for contaminants,” explained Dr. John Pote, Head of the Laboratory of Environmental Microbiology at the University of Geneva, who coordinated the laboratory study commissioned by UN Environment.
“Based on these results, we can therefore rule out that chemical contamination played a role in the fish kill, which should reassure the public that the farmed carp is safe to eat,” he added. These conclusions were also shared by Mr. Ahmed El-Olimat, Deputy Head of Quality and Laboratory Affairs in Ministry of Water and Agriculture in Jordan, who coordinated the test of the water samples sent by WHO to Jordan.
DNA tests run by the Swiss National Fish Disease Laboratory and Reference Laboratory for Notifiable Diseases found the presence of the Cyprinid herpesvirus (CyHV-3) in all fish samples examined, confirming Iraqi scientists’ suspicions that the fish kill was caused by a disease outbreak. They had observed white or brown patches on the gills of afflicted fish as critical clinical signs of an infection. Furthermore, the mortality only affected farmed carp and not wild fish. Virologic analysis commissioned by WHO and FAO – in Jordan and Italy respectively – also confirmed the Swiss laboratories’ findings.
“WHO was very concerned about this incident which could have posed a public health risk to communities in Babylon governorate and beyond. However, after confirming that the outbreak is due to a viral infection, WHO is confident that fish consumption has no effect on human health,” confirmed Mr. Mohamed Hamasha, Senior Environmental Health Expert and Mr. Soren Madison, Food Safety Adviser at WHO.
“High loads of Cyprinid herpesvirus DNA in the gill, kidney and brain fish tissue revealed that the carp suffered from the Koi Herpes Virus (KHV) disease,” affirmed Dr. Thomas Wahli, who heads the Swiss Reference Laboratory for Notifiable Diseases. “KHV is a very serious and lethal disease that is known to cause almost 100 percent mortality rates in carps,” he added. The Principal Virologist at the UK’s International Centre of Excellence for Aquatic Animal Health (CEFAS), Dr. Richard Paley, also agreed that “while overstocking and transient water quality issues such as low dissolved oxygen levels may have stressed the fish and helped propagate the virus, given the current information, one can reasonably conclude that the root cause of this mass fish kill episode is KHV disease.”
With Euphrates River water temperature dropping to 23-25°C in November, an optimal environment was created for the CyHV-3 virus, which flourishes between 16-28°C. Reports of similar small-scale fish kill incidents in multiple pockets in western and central Iraq further validated the occurrence of a wider epidemic.
“The outbreak may represent development of the disease in latently infected fish due to stressor events or perhaps more likely, based on the size of the event, introduction of infected animals into naïve stocks with no previous exposure or immune protection, indicating a recent introduction”, reckoned Dr. Paley.
“This is the first case of Koi Herpes Virus disease in Iraq, and it is a significant case report which will need to be notified to the World Organisation for Animal Health,” underlined Minister Alwan.
“We are pleased to have been able to get to the bottom of this difficult case and intend to build on this experience to improve our environmental surveillance and diagnostic capacity, particularly for viral diseases, so that we can properly investigate such events. Meanwhile, we need to control fish farm numbers and raise farmers’ awareness on the appropriate procedures to follow to prevent and rapidly contain similar outbreaks in the future,” he asserted.
(Source: UN Environment Programme)