West Nile virus has health officials 'concerned' as infected mosquitoes reach record highs and cases spread to 8 states
West Nile virus cases are being detected earlier than normal this year, in a warning sign that more people could be diagnosed with the mosquito-borne disease.
Cases don't typically appear until July, experts say — but nine have already been recorded in 2024 across the US.
In Tennessee and Kansas, both recorded their first cases in May — nearly two months ahead of schedule. Arkansas, Mississippi, Maryland, Michigan and Arizona have also recorded human cases, with Colorado being the latest — reporting its first on Wednesday.
Mosquitoes carrying the disease are also being spotted earlier than usual in states including Michigan and Connecticut, where the insects were at least a month ahead of schedule.
And they are being detected in record-breaking numbers in and around Las Vegas, worrying officials who say the higher number of infected mosquitoes raises the risk of more people being infected.
No deaths have been reported so far.
The above map shows the areas where West Nile virus has been spotted in mosquitoes (light blue) or in people (dark blue) so far this year. The season normally starts in late July for much of the country, but officials are concerned over this year's early start
About one in five patients develop symptoms of West Nile, which can include a rash, pictured above. Less than one percent of these go on to suffer from a serious form of the disease
Dr Thomas Moore, an infectious diseases expert in Kansas, told DailyMail.com it was certainly 'unusual' to see this many cases at this time of year.
But he said it was difficult to determine whether this would lead to a larger outbreak in the US because — as the virus has been in the country since 1999 — many people now already have immunity.
'To have a significant number of cases this early in the year, that may actually be a sign of global warming with mosquitoes being active earlier,' he said.
'This is something we can expect more of in the future, and not just with West Nile but also with dengue — which would be an indication that the situation is worsening.'
Yesterday, the CDC issued a health alert warning over a surge in dengue fever infections — saying this year's tally was already 'higher-than-expected'.
In Las Vegas, officials normally find 6,000 mosquitoes in traps from April to June. But this year they have already found 24,000, or nearly four-fold more than normal.
Out of the mosquito pools, or traps that caught the insects, 169 tested positive for West Nile virus — meaning at least one mosquito was infected — breaking the record set in 2019.
Of the nine patients reported nationwide so far, five have suffered from a severe and potentially deadly form of the disease.
Raising the alarm over the emerging situation, health officials in Kansas said: 'Although West Nile virus cases occur annually in [our state], the concerning trend this year is their unusually early appearance.
'Typically, West Nile virus cases begin in late July to early August, but we have already received reports of two cases this year [in May].'
In Michigan, officials echoed: 'This discovery [of infected mosquitoes] is earlier than in previous years, indicating a need for heightened vigilance and preventive measures.'
And in Las Vegas, officials said: 'This year is unprecedented. We've had the highest number of mosquito pools testing positive early in the transmission season.
'It's only the end of June or middle to end of June. This going to go on until October. So we're quite concerned.'
Vivek Raman, the environmental health supervisor for the Southern Nevada Health District, added: 'These are huge numbers of mosquitoes, and we’ve already identified a concerning number of them carrying the West Nile virus.'
The above shows the number of cases reported per year from 1999 to 2023. Cases have remained steady in recent years
West Nile virus cases have been rising in recent years, with about 2,500 cases recorded last year — more than double the 1,130 in 2022.
Experts say these figures are likely a vast undercount, however, because most people who catch the virus are not tested for it.
There are about 150 deaths from the disease every year.
West Nile virus is endemic to the US, with the first cases emerging in 1999 — likely after it was brought from another part of the word where the virus was more prevalent.
People catch the disease from the bites of infected Asian Tiger mosquitoes — shown by their black and white striped markings — which pick up the virus from birds.
About one in five people exhibit symptoms, such as a fever, headache and a spotty rash covering the trunk, head, neck, fingers and toes.
These can last a few days to several weeks, with patients treated using fluids, bed rest and over-the-counter painkillers.
Of those with symptoms, less than one percent will develop a severe form of the disease — called West Nile neuroinvasive disease (WNND) — which can be deadly.
In this, the virus infects the brain and causes encephalitis, or inflammation of the organ, leading to seizures, disorientation and coma.
About three to 15 percent of WNND patients die from the disease, with death sometimes caused by the virus infecting and shutting down cells needed to send impulses to instruct the body to breathe.
Young children, adults over 50 years old and those who have weaker immune systems are most at risk of this severe form of the disease.
Experts say mosquitoes are active earlier this year because of warmer and wetter weather in many parts of the US.
They are expected to remain active until October, during which period people are at heightened risk of infection.
And there are also concerns over other mosquito-borne diseases, like dengue fever.
For protection against West Nile virus, officials have advised people to wear insect repellant, as well as long-sleeve tops and pants in the evenings and early mornings — when mosquitoes are most active.
Individuals have also been advised to remove any standing water near their home, as this can be a place where mosquitoes can breed.
