This is a photo showing the head of a culex under the microscope. (Xinhua/Zhang Chao)
by Eric J. Lyman
ROME, Sept. 9 (Xinhua) -- Longer, more humid, and warmer summers, combined with mild winters are helping facilitate the spread of tropical and semitropical diseases, including the West Nile Virus, which has so far this year infected five times as many people as in 2017.
As of the end of August, around 130 cases of the mosquito-borne disease had been recorded in Italy, more than in any other European country. Serbia, Greece, Hungary, and Romania have also experienced higher-than-normal number of cases, according to the United Nations World Health Organization (WHO).
Italy has also seen a rise in the frequency of other diseases this year, including measles and related diseases such as encephalitis and pneumonia. But scientists say those diseases are spreading mostly because of controversial new government policies making some vaccinations for young people in schools voluntary.
However, in the case of the West Nile Virus, the culprit is the spread of mosquitos from the "Culex" genus.
The spread has evidently been on the rise in Italy: the country's first recent case of West Nile Virus came a decade ago, and there have been at least a few cases of the disease in the country every year since then until a big rise last year and then a dramatic increase in 2018 compared to 2017.
"There are various hypotheses that could help explain the reasons for the increase," Massimo Galli, president of SMIT, the Italian Society for Infectious Diseases, told Xinhua. "The summers are longer and warmer now, the winters more mild, and there is more variation between rainy days followed by dry periods."
Giovanni Rezza, director of the Department for Infectious Diseases at Italy's Higher Institute for Health, a research institute, said that while it was impossible to determine that a specific weather phenomenon is tied to climate change he "could not rule out" that the increasing reach of the disease-carrying mosquitos was tied to climate change.
Unlike measles, the West Nile Virus cannot be passed from one person to another -- only from contact with mosquitos. The disease is usually not fatal: only around 20 percent of those infected show symptoms, which include a persistent fever. The disease is more serious in around 1 in 150 cases, where it can evolve into a potentially fatal illness, according to the United States-based Center for Disease Control.
But so far this year, at least 12 people in Italy have died from the disease, compared to just one death a year ago.
According to Rezza, the weather of one year affects the number of mosquitos the next year. For example, this year's outbreak of West Nile Virus is due in part to the hot summer in 2017, which allowed the mosquitos to spread, and the mild winter, which failed to kill off the majority of the mosquito eggs, producing more mosquitos the following year. Barring an unexpectedly severe winter, this year's long, warm summer could result in more disease-carrying mosquitos in 2019.
"The disease can be spread until October, but we probably reached the peak in August," Rezza said in an interview. "It's impossible to know the future, but outbreaks like the one this year could become more common."