Virus World

Climate change is shifting the ranges of many disease-carrying species like ticks and mosquitoes. Scientists warn that the U.S. is underprepared for a potentially devastating surge in infections. In the summer and fall of 2021, West Nile virus spread rapidly through Arizona’s Maricopa County and other areas of the state. The outbreak, with more than 1,700 cases reported and 127 deaths. was the largest in the United States since the mosquito-borne virus first emerged in this country in 1999. But with the nation facing a far larger public health crisis with the Covid-19 pandemic, it went almost unnoticed. Even before Covid-19 arrived, the public health response to diseases transmitted to humans by vectors like fleas, ticks and mosquitoes — including West Nile, Zika, dengue fever, Lyme disease, and others — was muted, perhaps because the number of reported cases has been relatively low, and the public largely unaware of the health risks such diseases pose. With climate change accelerating, however, shifting the ranges of many disease-carrying species and sharply increasing infections, scientists and others warn that the nation’s public officials, as well as hospitals and doctors, are underprepared for a potentially devastating surge in infections. Research on vector-borne diseases and disease surveillance, they note, are underfunded by federal and local governments, leaving the country vulnerable to outbreaks.

“Without sustained funding in local vector control and surveillance, it ends up stymieing that response of looking for the threats before they become really huge causes for concern for local public health,” said Chelsea Gridley-Smith, director of environmental health for the National Association of County and City Health Officials (NACCHO). In the United States, cases of 17 different vector-borne diseases have been reported to the Centers for Disease Control and Prevention, and nine pathogens new to the country have been identified since 2004, according to a 2020 report by the agency, which noted that the data for 2019 and 2020 might be incomplete due to underreporting during the Covid-19 pandemic. Reported cases of vector-borne diseases more than doubled from 2004-2019, to more than 800,000 cases. But those figures are almost certainly an undercount, CDC officials said in a presentation to Congress last year. Only 2% to 3% of West Nile cases and about 10% of Lyme disease cases are reported, said Lyle Petersen, the director of the CDC’s Division of Vector-Borne Diseases in Fort Collins, Colo. Overall, cases of vector-borne diseases are probably underreported by 10-fold to 80-fold, according to Benjamin Beard, the CDC division’s deputy director.

Petersen noted that addressing vector-borne disease involves formidable challenges, including a lack of vaccines for diseases found in the continental United States; the difficulty in diagnosing some diseases in their early stages; and the sheer number of emerging pathogens. Tick-borne diseases comprise the largest share of vector-borne diseases by far — over 80% of reported cases are caused by ticks. Longer summers, rising temperatures, and the expanding ranges of tick species such as Ixodes scapularis, the black-legged tick, and Amblyomma americanum, the lone star tick, are leading to an increased chance of human exposure to pathogens over a larger geographic area. The range of Ixodes scapularis, a tick that transmits Lyme and other diseases, expanded greatly over two decades, with the number of counties with established populations more than doubling from 1996 to 2015.

Similarly, milder year-round temperatures mean that some mosquitoes may overwinter or emerge earlier in the spring. In the case of West Nile, this affects not just the mosquitoes carrying the virus but the virus itself, which replicates faster in warm temperatures. “So the mosquitoes actually are more infectious to people when they bite them,” Beard said. Nelson Nicolasora, medical director for the infectious disease program at Banner University Medical Center in Phoenix, said that while the 2021 West Nile virus outbreak was “nothing like” the Covid-19 pandemic, the illness was “life-changing” for people who suffered debilitating neurological disease. West Nile usually causes mild, flu-like symptoms, but about 1 in 150 people who are infected will develop severe neuroinvasive disease. “It can be devastating,” Nicolasora said. Two of his patients died during the 2021 outbreak, he said, and others faced serious short-term and longer-term effects: Some required a ventilator to breathe, or rehabilitation to regain the ability to walk. Irene Ruberto, vector-borne and zoonotic disease program manager at the Arizona Department of Health Services, said that even though public health officials in the state were aware of the cyclical nature of West Nile virus infections from year to year, they had no idea the infection rate would be so high in 2021. It’s difficult to predict how many infections will occur in a given year, Ruberto said, because many factors are involved, including mosquito density, local environments, and the climate.

“We do know that birds play a role,” acting as an amplifying host for the virus, Ruberto said, which adds complexity to understanding virus transmission. While West Nile is transmitted to humans by mosquitoes, mosquitoes get the virus through biting an infected wild bird. And different species of birds vary in their ability to transmit the virus once they’re infected. Ruberto said the state health department in Arizona doesn’t on its own have the funding or the capacity to analyze the 2021 outbreak to understand the factors that drove it. Instead, she said, the department is working with the CDC and universities to study the 2021 data and develop a model to predict future outbreaks. However, Ruberto said she’s even more concerned about the emergence in her state of another vector-borne disease: dengue fever. In 2022, two locally transmitted cases of dengue were discovered in Arizona, the first appearance of the disease in the state in modern times. Though dengue — known colloquially as “breakbone fever” because of the severe joint pain and muscle spasms it can cause — is also transmitted by mosquitoes, it differs from West Nile in an important way: The virus can be spread from one infected person to another person through a mosquito bite...

A protein that is critical in controlling replication of West Nile and Zika viruses—and could be important for developing therapies to prevent and treat those viruses—has been identified by a Georgia State University biologist and his research group.

The researchers found Z-DNA binding protein 1 (ZBP1) is a sensor that plays a significant role in triggering a robust immune response when it detects a viral infection within cells. The Georgia State study, published in the journal Frontiers in Microbiology, found ZBP1 is essential for restricting both West Nile and Zika virus replication, and that it prevents West Nile-associated encephalitis (inflammation of the brain) in mice. The absence of ZBP1 in mice leads to 100 percent mortality when infected with even a non-disease-producing strain of West Nile Virus, the study found. "It's significant because you take a virus that has never been shown to kill anything and if you block this protein the virus will just kill everything," said Mukesh Kumar, assistant professor of biology and senior author of the study. "We discovered that when cells are infected with viruses such as Zika and West Nile, they respond by triggering necroptosis, a form of programmed cell death, via ZBP1 signaling. This inhibits  viral replication  and spread, allowing the immune system to clear the virus."

Kumar said the findings could present new treatment strategies for viruses that can infect the central nervous system by modulating ZBP1 expression. Subsequent research by Kumar's team will explore effectiveness against similar viruses such as Eastern Equine Encephalitis and Powassan virus. West Nile Virus is the leading mosquito-born disease and cause of viral encephalitis in the United States, with more than 50,000 people affected, including 480 cases reported in Georgia, according to the Centers for Disease Control and Prevention. There have been 2,330 associated deaths since it first reached the country in 1999. The Culex species of mosquito responsible for spreading it is common throughout the world.

Zika, which is spread by the Aedes mosquito that has been found as far north as Florida and Texas, can cause serious neurological diseases such as Guillain-Barre syndrome, which causes the body's immune system  to attack the nervous system. Birth defects such as microcephaly, an abnormally small head and brain can result. Most people who get Zika or West Nile don't get sick thanks to the body's natural immune response and may not know they've been infected, meaning their cases probably don't get reported. Of the West Nile cases reported in the U.S., nearly 50 percent invade the nervous system leading to life-threatening or -altering consequences such as encephalitis. Drug treatments are often ineffective once a virus reaches the brain, but Kumar hopes enhancing host ZBP1 expression within the central nervous system could clear the  virus from the brain and prevent severe disease associated with neuroinvasive viral infections such as West Nile and Zika....

Study Published in Frontiers in Microbiology (Sept. 11, 2019):

https://doi.org/10.3389/fmicb.2019.02089

The female mosquito needs your blood to grow her eggs. Please don’t feel singled out. She bites everyone. There is no truth to the myths that mosquitoes prefer women over men or blondes and redheads over those with darker hair. She does, however, play favorites. Type O blood seems to be the vintage of choice. Stinky feet emit a bacterium that woos famished females, as do perfumes. As a parting gift, she leaves behind an itchy bump (an allergic reaction to her saliva) and potentially something far worse: infection with one of several deadly diseases, including malaria, Zika, West Nile, dengue and yellow fever.

Two human cases of West Nile virus have been reported in New York as the virus has been detected in a record number of mosquitoes in the city, health officials said Tuesday.  Across the city's five boroughs, 1,068 mosquito pools have tested positive for the virus, according to the New York City Department of Health and Mental Hygiene. The city recorded 779 positive pools at the same time last year. The two human cases were reported in Brooklyn and Queens, the health department said in a statement. The West Nile virus is most commonly spread to people through the bite of an infected mosquito, according to the US Centers for Diseases Control and Prevention. Those cases happen during mosquito season, which starts in the summer and continues through fall, the CDC said.  "We are in the height of West Nile virus season, but there are things you can do to decrease your risk of being bitten," New York City Health Commissioner Dr. Ashwin Vasan said. Using an insect repellent and wearing long sleeves and pants, especially when outside during late and early hours, may help prevent the risk of getting bit, Vasan explained. 

There is no vaccine for the virus, so preventative measures are the most effective way to avoid infection. Symptoms of West Nile infection include fatigue, fever, headache, body aches and rash. However, 80% of infected people do not display any symptoms, according to the CDC. In rare cases, the virus can also be spread through blood transfusions, organ transplants, exposure in a lab setting or from mother to infant. Less than 1% of infected people develop a serious neuroinvasive illness, such as encephalitis (inflammation of the brain) or meningitis (inflammation of the protective membranes covering the brain and spinal cord), according to the CDC. As of August 9, a total of 54 human cases of the virus disease have been reported to the CDC this year. Last year, 2,695 human cases were reported to the agency.

CNN's Aya Elamroussi contributed to this report.

West Nile Virus Spreads In Los Angeles - Los Angeles, CA - More mosquitoes in the region tested positive for the potentially deadly virus, and authorities are asking residents to take precautions. The hot weather is just egging the mosquito season on, and officials Friday announced the spread of the West Nile Virus in the San Fernando Valley. 

According to the Greater Los Angeles County Vector Control District, 11 new mosquito samples tested positive for West Nile virus. Mosquitos carrying the virus were found in Woodland Hills, Montebello, Santa Fe Springs, and South Whittier. In all, mosquitoes with West Nile Virus have been found within the district's service area to 25 this year. Already, they have been found in Northridge, Reseda, Canoga Park, Winnetka, Carson, Cerritos, Granada Hills, La Mirada, Lakewood, Long Beach, Montebello, Santa Fe Springs, Signall Hill, South Whittier, West Hills, and Woodland Hills.

People infected with the virus can experience a myriad of symptoms, ranging from no symptoms to seizures and death. West Nile virus is a leading cause of severe infections of the nervous system among adults older than age 50 in Los Angeles County. WNV is transmitted to people and animals through the bite of an infected mosquito. There is no cure for WNV.  One in five persons infected with the virus will exhibit symptoms, which can include fever, headache, body aches, nausea, or a skin rash. These symptoms can last for several days to months. One in 150 people infected with the virus will require hospitalization. Severe symptoms include high fever, muscle weakness, neck stiffness, coma, paralysis, and possibly death.

So far this year, 57 WNV human cases have been reported in California, four of which were identified by the Los Angeles County Department of Public Health.

Weekly Update of WNV cases in California available at:

http://www.westnile.ca.gov/