When Italian doctors diagnosed a neurological disease due to West Nile virus (WNV) in a Sicilian man, they immediately set off a chain of events leading to massive tests on horses, dogs, birds and mosquitoes at proximity to find the source of the epidemic.

As part of a One Health approach, the new Intensive Biosecurity initiative aims to combine the efforts of physicians, veterinarians, biologists and insect specialists to track down WNV outbreaks to better control a potentially fatal disease affecting several species, including horses and humans. said Giuseppa Purpari, PhD, at the A. Mirri Experimental Zooprophylactic Institute of Sicily, Palermo, Italy.

“This Italian experience is a good example of cooperation between various areas of public health,” said Purpari and colleagues in Medicine and veterinary sciences earlier this month.

Likely native to Africa, WNV has spread to other continents in recent decades, likely through infected migratory birds, they said. Birds transmit the virus to biting mosquitoes, which then pass it on to humans and animals, mainly horses and sometimes dogs. Although dogs, humans, and horses are all dead end hosts, which means they can’t pass the virus elsewhere, they can still get sick and even die from a neurological form of the disease.

Sicily’s first human WNV case triggers hundreds of multispecies tests

When a 38-year-old Sicilian man presented to the emergency room in 2016 with neurological signs of WNV infection, doctors tested his blood, serum, urine and cerebrospinal fluid. Although the polymerase chain reaction (PCR) tests for WNV were negative, antibody tests in his serum and cerebrospinal fluid were positive, Purpari said.

Once the scientific team had the positive results in their hands – the first human case in Sicily – they adopted a one-of-a-kind WNV management model recently put in place by Italian public health authorities. Less than a month earlier, the country’s health ministry had adopted a new multidisciplinary approach: the “Integrated national WNV surveillance plan”, presented in government circular 10/08/2016.

“The plan provides for integrated medical, veterinary and entomological surveillance, and it represents a unique model in Europe,” said Purpari and his colleagues.

Authorities have ordered extensive testing on several species, all of which live within a specified range of the human patient’s home on the island of Sicily, they said. They took blood samples from 11 horses, 271 chickens and two dogs and collected 2,704 mosquitoes from six locations in and around the man’s house.

Both dogs and two horses had positive antibody tests but negative reverse transcription PCR (RT-PCR) blood tests, Purpari said. None of the chickens or other horses tested positive.

Mosquitoes underwent pooled RT-PCR testing; all of the results were negative, she said.

Experts: One-Health approach identifies local source of WNV, equine vaccinations recommended

Despite the negative PCR results, especially in mosquitoes, the combined evidence pointed to a local epidemic source of WNV, the researchers said. The fact that the man had not traveled outside of Sicily recently and that nearby dogs and horses were also infected was a strong indication that the virus was alive and circulating in Sicily itself.

In addition, the main vector of WNV, the Culex Pipiens mosquito, was by far the most common mosquito species captured by researchers in the region, which was abundant in the insect’s main habitats: basements, abandoned buildings, henhouses, stables and animal shelters, etc. they stated. PCR test results depend on viral life cycles, and it is not uncommon to have a negative molecular result, Purpari explained. Antibody tests are not possible in mosquitoes.

Further investigations led the researchers to a wildlife sanctuary near the patient’s home with salt marshes where migrating birds frequently roost during migration. “It represents suitable habitat for mosquito larvae and provides a variety of hosts, which mature insects can feed on,” they said. “For these reasons, it represents a potentially high risk area for WNV infection. “

Keeping humans, horses and other animals away from mosquitoes is the most effective biosecurity method to prevent the spread of WNV, the team explained. Vaccinating horses can also help protect them from infections. “Equine vaccination may be suggested in areas characterized by environmental and climatic conditions particularly suited to mosquitoes, such as the one described here,” they said.

WNV in Europe: an overview

This is not the first time that Europe has seen WNV in humans, according to the research team. Almost 400 people were diagnosed in Romania in 1996, and the number has steadily increased since.

But epidemics are sporadic, they said. Cases were high in Europe in 2012, 2013 and 2018, but low in between.

From spring 2020 to the last report on September 23, 2021, the European Union reported nearly 400 human cases of WNV resulting in 38 deaths in Austria, Germany, Greece, Hungary, Italy, the Netherlands, Romania and in Spain. Authorities detected 200 cases of WNV in horses and six cases in birds during the same period, mainly in Spain, but also in Austria, Bulgaria, France, Germany, Greece, Hungary, Italy and Portugal.

Italy experienced its first outbreak of WNV in horses in Tuscany in 1998, resulting in neuroinvasive disease (WNND) in 14 horses. In 2010, five Sicilian horses fell ill with WNND, and canine testing at the time indicated that the virus had been present in the region for seven months before the equine outbreak, the researchers said.

Italian model of WNV surveillance: proactive and collaborative

Italy chose to adopt combined surveillance plans gradually from 2001, with the last directive in 2016 including a comprehensive One Health approach aimed at in-depth multi-species testing around any outbreak site.

“WNV requires a collaborative, multidisciplinary and integrated methodology, as advocated by the ‘One Health’ approach which recognizes the close interrelationship between the environment, human and animal health,” said Purpari and colleagues.

This includes ensuring the safety of substances of human origin (SoHO) – human organs, tissues, blood and cells used in medical treatments – that may have been exposed to the virus, the team explained.

“The integrated national WNV surveillance plan has proven to be a key point in implementing timely control measures against the spread of this infection and the risk of human transmission by early detection of viral circulation and triggering both vector control and SoHO security measures, ”they said.

The study, “First neuro-invasive human case of West Nile disease in southern Italy: results from the“ One Health ”approach,” was published on September 10, 2021 by Veterinary Medicine and Science.