Israel West Nile virus update

August 4, 2024

The latest from the Israel Ministry of Health on the West Nile virus outbreak shows that through August 4, 784 confirmed cases and 56 deaths have been reported year to date.

The cities reporting the most cases include: Tel Aviv - Jaffa (83), Petah Tikva (66) and Herzliya (46).

West Nile fever typically appears toward the end of summer and the beginning of fall (August through November). Peak transmission in Israel is usually in the third week of September. There are only a few cases throughout the other months of the year. Transmission peaked a month earlier this year, but it is still too early to say if the number of active cases has increased or if the peak of transmission has shifted. 

West Nile disease is caused by an RNA virus from the Flavivirus family. West Nile viruses with varying genetic makeup arrive in Israel via flocks of migratory birds. Every year, Israeli scientists discover new genotypes that closely resemble viruses from Europe, Russia, and Africa while bearing less resemblance to viruses that circulate in the U.S.

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There are presently five identified West Nile virus lineages. Only two of these can infect people. Many natural factors, such as the species of mosquitoes or birds, affect the spread of the virus. Other factors include variance between mosquito species (different species vary in the efficacy of transmission), rivalry among mosquitoes, natural enemies of mosquitoes, and the availability of food.

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Other factors that influence spread include atmospheric conditions such as moisture, rainfall, temperature (global warming), standing water, accessibility of water sources, and human-related factors such as global commerce, rapid transportation, and the condition of the immune system of the human host.

There are also unanticipated factors that can alter the spread of the virus. As a result, it is impossible to predict how widespread the virus will be in a certain year based on previous years.

West Nile has long been present in Israel. After the initial West Nile disease outbreak in Israel between 1950 and 1954, a second outbreak was found in 1957. Later, viral spread rose significantly in the 1970s and 1980s. Following its discovery in birds in 1997, a widespread outbreak struck the following year, mostly impacting flocks of geese for fattening. 2000 saw the occurrence of a pandemic with over 400 cases. Diagnoses of dozens of cases have been made every year since 2001.

The main area where the virus is most active is the coastal plain, which stretches from Nahariya in the north to Kiryat Gat in the south. Furthermore, endemic activity is still present in the Arava region, which stretches from the Dead Sea to Eilat. The activity regions' geographic distribution, patient volume, and disease severity may change from one year to the next.

This year, the outbreak started sooner than normal. The number of cases is significantly higher than the multi-year average for this month (June) of this year (2024); this is particularly true of the number of reported hospitalizations.