I don't think Alexander died from West Nile fever. I read the article
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3034319/ and it didn't convince me. I see several problems there:
1) The author relies on Plutarch but Plutarch's source about Alexander's death is the so-called Royal Diary which is the main record of Alexander's journey. But we know that Antipater's son Cassander tried to censor all historical records, no doubt including this one. If there was any mention of Alexander's poisoning, Cassander would alter it. Therefore we have to be skeptical about reports of Alexander's fever.
2) Any theory about viral infection killing Alexander is dubious because ancient historians didn't record any other inexplicable deaths at that time. What is the probability that only Alexander (and Hephaestion a year ago) died of inexplicable fever?
3) The author of the article about West Nile fever admits that this hypothesis has some shortcomings. He wrote: "Still, the possibility that West Nile virus killed Alexander is mitigated by the fact that he fell ill in May. Although the virus may have occurred at that time, most recent human cases in Israel occurred in July to September, with only a few cases occurring in June."
4) The death rate for West Nile fever is very low:
In about 80% of infections people have few or no symptoms. About 20% of people develop a fever, headache, vomiting, or a rash. In less than 1% of people, encephalitis or meningitis occurs, with associated neck stiffness, confusion, or seizures.
https://en.wikipedia.org/wiki/West_Nile_fever
5) And finally, the main argument in that article was the incident with ravens: "… when he arrived before the walls of the city he saw a large number of ravens flying about and pecking one another, and
some of them fell dead in front of him." The author of the article then speculates: "One wonders if an influx of migratory birds might have served as reservoirs of West Nile virus and infected ravens in Babylon, causing
a massive die-off."
However, the original report didn't say there was "a massive die-off" but only that "some of them fell dead". That's a big difference. More importantly, there is a much simpler explanation for this behavior. When Alexander saw this incident he was entering Babylon in the spring. And it's common knowledge that:
Ravens, like crows, are capable of getting quite aggressive, especially during their breeding season, which lasts from
mid-February to May. They get aggressive towards anyone approaching their nest or encroaching upon their territory, be it humans, other ravens, or any birds.
https://animalqueries.com/do-ravens-kill-each-other/
And they can also kill each other:
Ravens kill each other for various reasons, such as to protect themselves, to invade nests, and to get food. They are quite competitive and use their beaks to attack each other. Mostly ravens kill each other over food, and sometimes, they attack each other to defend or protect their mates.
https://animalqueries.com/do-ravens-kill-each-other/