Effective strategies for eradicating West Nile Virus in Israel and beyond

It may be due to global warming, more humid weather, a larger number of migratory birds landing here to rest on their way to the North, or more standing water, but even the experts can’t explain why the West Nile virus is worse this summer than in previous years. What is certain is that so far this year, 299 people have been diagnosed in Israel, and with 31 people aged 70 and over or with weak immune systems having died from West Nile Fever (WNF), many Israelis have begun to panic. This can be compared to 23 cases of infection in 2020, 34 in 2021, 25 in 2022, and 53 in 2023.

People of all ages are running to buy electric mosquito zappers and chemical devices for their homes to spread repellents into the air. Some of the purchases are not merely ineffective; they may even attract the Culex female blood-sucking insects – vectors that have been infected by the birds.

At least the virus doesn’t pass from one person to another or from the bitten individual to mosquitoes. The season usually lasts from June to October or even November. Israel is not the only country to suffer from West Nile. It is regularly reported in parts of the US, throughout Africa, parts of Europe and the Middle East, west Asia,

Australia, Canada, and Venezuela typically go along major migratory-bird routes, with the largest outbreaks occurring in Greece, Russia, Romania, the US, and Israel. Children are bitten somewhat

more often than adults, and women more than men, because of short-sleeved blouses, shorts, and short skirts, while men are usually more covered up, so the mosquitoes have less opportunity to bite them, according to the prominent Hebrew University of Jerusalem (HU) parasitologist Prof. Kosta Mumcuoglu.

WNF originates in wild birds, and it is transmitted to humans and animals through the bite of mosquitoes that feed on infected migrating birds. Most people – 80% – are asymptomatic; 19% do have some light symptoms; and one percent contract the disease, explained Mumcuoglu. When there are symptoms, in most cases it is a mild, flu-like illness characterized by fever, headache, joint and muscle pain, conjunctivitis, and sometimes nausea and diarrhea that go away without intervention.

While most people with fever due to WNF recover completely, fatigue and weakness can last for weeks or months. Meningitis is a rare complication, and in even rarer cases, the disease is fatal.

MUMCUOGLU HAS been studying head lice, fleas, ticks, and other creepy crawlies for decades. With degrees from the University of Basel in Switzerland, he came to Israel in 1975 as a visiting scientist at HU’s medical entomology department and even served as a visiting scientist at the pest-control department at the Agricultural College of Teheran University.

Following a second stint in Zurich, he returned to Jerusalem, where HU appointed him as a research biologist in its zoology department. Fluent in English, German, French, Hebrew, Greek, and Turkish, he has served as a professor in Turkish universities since 2004 and, since 1985, as a parasitologist at the HU-Hadassah Medical School.

Among his Jerusalem team’s projects is the treatment of patients with chronic wounds using disinfected fly larvae (maggot debridement therapy) and medicinal leeches to salvage compromised microvascular free-tissue transfers, replanted digits, ears, lips, and nasal tips due to venous congestion. He teaches entomology to physicians, nurses, pharmacists, veterinarians, and biologists.

The Environmental Protection Ministry regularly captures mosquitoes that are later diagnosed in the Health Ministry laboratories as being infected with the West Nile virus. This year, they have been found in several locations in the lowland area, between the southern coast of the Mediterranean; the Yavneh, Lod, and Ramle areas; Tel Aviv, Herzliya, Kiryat Ono, Petah Tikva, the Lev Hasharon Regional Council; Even Yehuda; Eilat; and in the Ayalot and Modi’in regional councils. The ministries have instructed the local authorities to take action, including spraying with insecticide and eliminating standing water, where mosquitoes breed.

Mumcuoglu warned, in an interview with The Jerusalem Post, that in the summer, sources of stagnant water – even a small amount in courtyards, gardens, balconies, and plates under flower pots and planters – can be fertile ground for the reproduction and development of mosquitoes. He advises people to change the water or empty containers, such as flower vases and pet-drinking bowls, at least once a week; to cover swimming pools; and to clean and empty gutters. It is imperative to find, remove, puncture, or turn over any container that accumulates water, such as old tires, buckets, and barrels.

He insisted that only a joint effort by all the public and authorities will result in a quick, long-term solution that will make it possible to significantly reduce the nuisance of mosquitoes in the environment, thereby reducing the risk of being stung and getting infected.

The HU parasitologist noted that people living on lower floors are at higher risk of allowing mosquitoes inside. “Wear long-sleeved, light clothing and socks. Though mosquitoes bite mostly in the middle of the night, don’t leave windows and doors open after 5 p.m., when they start being active – entering houses and biting those staying in the open air. Install mosquito screens on at least one window of each bedroom, and use those windows for ventilation of the room.

Leave on the fans and air conditioners in the bedrooms to try to prevent the bugs from settling on sleepers. If mosquitoes are still present in the bedroom, electric devices that slowly release insecticides and affect the activity of the mosquitoes can be used.

“Roll-on and sprayed-on insect repellent that should be used only in the open parts of the body may help, but due to perspiration, they are ineffective unless reapplied after a short time.”

DEET insect repellent, used to prevent bites from insects such as mosquitoes, biting flies, fleas, and small flying insects, is a colorless liquid that has a faint odor and does not dissolve easily in water; it is the most effective. Most people, however, buy essential oils that are potent for only a short time and should be applied more frequently during the hours when mosquitoes are active, he added.

Mumcuoglu noted that various research institutes, including some at HU, have been working hard to develop technologies to prevent mosquitoes from biting – even natural insecticides and repellents, and changing the male mosquitoes’ chromosomes so the females they mate with will produce only males. However, while these may work under lab conditions, they haven’t yet been proven in nature, so for now, they wouldn’t be effective in fighting WNF, he said.

West Nile Virus on the rise in Israel

In Israel, there is a lot of discussion about the West Nile virus, but some people are also concerned about dengue fever, another viral infection that mosquitoes spread. However, Mumcuoglu assures them that they should not worry about dengue. “The Health Ministry has announced a handful of cases of infection with the potentially deadly virus – transmitted by the Asian tiger mosquito (existing also in Israel) – in people who returned from tropical countries (including Egypt). For the virus to be established in Israel, there must be large numbers of infected mosquitoes and lots of people with the virus,” he said.

“All those planning visits to affected areas, including southeast Asia, Latin America, and Africa, are examined and counseled by medical specialists in travel and tropical medicine who give them vaccinations and follow up with them when they return, to make sure they did not catch the disease. While travelers have come home with dengue, there has been no local infection.”

He explained that “our native mosquitoes have not yet been infected with the virus, and even if they bite an infected person returning from tropical countries, most of the mosquitoes die after the first blood meal and egg laying; thus, the risk of them biting a second time and transmitting the virus is very small. However, the health and environment experts have to keep their eyes on it.”

So at least that’s good news. A study just published by Taiwan researchers in PLOS Neglected Tropical Diseases, titled “Risks of anxiety disorders, depressive disorders, and sleep disorders in patients with dengue fever: A nationwide, population-based cohort study,” has surprisingly concluded that dengue virus has been linked to a significant number of mental problems, including depression, sleep disorders, and anxiety.

As it stands, since October 7, too many Israelis are already struggling with such emotional issues, even without the dengue virus in the country.