The West Nile virus has caused outbreaks of West Nile fever in countries on a number of continents since its discovery in 1937 in Uganda.
The West Nile virus has caused outbreaks of West Nile fever in countries on a number of continents since its discovery in 1937 in Uganda.
The first cases of West Nile disease in the United States occurred in 1999 in New York. In the first three years only a small number of human cases were diagnosed, all in the Eastern or Southern U.S. (149 cases and 19 deaths, 1999–2001). In 2002, the disease exploded to most of the lower 48 states, causing 4,156 diagnosed cases of which 284 died. The disease continued to spread, reaching all but three states by 2006. The first case detected in Maine occurred in 2012. [1] The single cases detected in Hawaii in 2014 and in Alaska in 2018 were likely imported. [2] [3]
In the period from 1999 to 2018, the United States had 2,330 total deaths out of 50,830 diagnosed cases, giving a case fatality rate of 5%. [1] The worst years were 2003 for the most cases with 9,862 and 2012 for the most deaths with 286. [1] Most cases are thought to go undiagnosed. The WHO claims that about 80% of cases are asymptomatic. [4] Half of all cases (48.5%) diagnosed in the U.S. lead to neuroinvasive symptoms. Over 90% of deaths occurred in cases with neuroinvasive disease. [1] After several cases of West Nile disease transmitted by blood transfusion, the U.S. began testing all blood donations and dozens of presumed cases are found each year. [5] Some West Nile cases resulted from organ transplants and some but not all organs/donors are tested. [6]
As of 2020, the disease outbreak is considered ongoing and essentially endemic. As well as humans, countless birds and over 27,000 horses have been infected, providing additional reservoirs for the virus. [7]
One human death occurred in 1999. In 2002, ten human deaths out of 416 confirmed and probable cases were reported by Canadian health officials. In 2003, 14 deaths and 1,494 confirmed and probable cases were reported. Cases were reported in 2003 in Nova Scotia, Quebec, Ontario, Manitoba, Saskatchewan, Alberta, British Columbia, and the Yukon. In 2004, only 26 cases were reported and two deaths; however, 2005 saw 239 cases and 12 deaths. By October 28, 2006, 127 cases and no deaths had been reported. One case was asymptomatic and only discovered through a blood donation. In 2007, 445 Manitobans had confirmed cases of WNV and two people died with a third unconfirmed but suspected. [8] Summer of 2012 saw widespread viral penetration in Canada, coast to coast. [9] 17 people have either tested positive or are suspected of having the virus in Saskatchewan, and only one person has tested positive in Alberta. [10] Saskatchewan has reported 826 cases of WNV plus three deaths. [11] The spread of West Nile Virus infected mosquitoes to British Columbia for the first time was reported in 2009 [12]
| Year | Infections | Deaths |
|---|---|---|
| 2010 | 332 | ≥38 [14] [15] |
| 2011 | 125 | ≥9 [16] |
| 2012 | 267 | ≥3 [17] |
| 2013 | 273 | ≥1 [19] |
| 2014 | 75 | |
| 2015 | 122 | 2 |
| 2016 | 226 | 27 |
| 2017 | 201 | 25 |
| 2018 | 1549 | 166 |
| 2019 | 425 | 52 |
| 2020 | 316 | 37 |
| 2021 | 139 | 9 |
| 2022 | 394 | 21 |
| 2023 | 707 | 67 |
West Nile fever is an infection by the West Nile virus, which is typically spread by mosquitoes. 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. Recovery may take weeks to months. The risk of death among those in whom the nervous system is affected is about 10 percent.
The West Nile virus quickly spread across the United States after the first reported cases in Queens, New York, in 1999. The virus is believed to have entered in an infected bird or mosquito, although there is no clear evidence. The disease spread quickly through infected birds. Mosquitoes spread the disease to mammals. It was mainly noted in horses but also appeared in a number of other species. The first human cases usually followed within three months of the first appearance of infected birds in the area except where cold weather interrupted the mosquito vectors. Since the virus has become widely established in the U.S., an average of 130 deaths a year have occurred.
La Crosse encephalitis is an encephalitis caused by an arbovirus which has a mosquito vector.
Eastern equine encephalitis (EEE), commonly called Triple E or sleeping sickness, is a disease caused by a zoonotic mosquito-vectored Togavirus that is present in North, Central, and South America, and the Caribbean. EEE was first recognized in Massachusetts, United States, in 1831, when 75 horses died mysteriously of viral encephalitis. Epizootics of EEE in horses have continued to occur regularly in the United States. It can also be identified in donkeys and zebras. Due to the rarity of the disease, its occurrence can cause economic impact beyond the cost of horses and poultry. EEE is found today in the eastern part of the United States and is often associated with coastal plains. It can most commonly be found in East Coast and Gulf Coast states. In Florida, about one to two human cases are reported a year, although over 60 cases of equine encephalitis are reported. In years in which conditions are favorable for the disease, the number of equine cases is over 200. Diagnosing equine encephalitis is challenging because many of the symptoms are shared with other illnesses and patients can be asymptomatic. Confirmations may require a sample of cerebrospinal fluid or brain tissue, although CT scans and MRI scans are used to detect encephalitis. This could be an indication that the need to test for EEE is necessary. If a biopsy of the cerebrospinal fluid is taken, it is sent to a specialized laboratory for testing.
Influenza-like illness (ILI), also known as flu-like syndrome or flu-like symptoms, is a medical diagnosis of possible influenza or other illness causing a set of common symptoms. These include fever, shivering, chills, malaise, dry cough, loss of appetite, body aches, nausea, and sneezing typically in connection with a sudden onset of illness. In most cases, the symptoms are caused by cytokines released by immune system activation, and are thus relatively non-specific.
Mosquito-borne diseases or mosquito-borne illnesses are diseases caused by bacteria, viruses or parasites transmitted by mosquitoes. Nearly 700 million people contract mosquito-borne illnesses each year, resulting in more than a million deaths.
Kunjin virus (KUNV) is a zoonotic virus of the family Flaviviridae and the genus Flavivirus. It is a subtype of West Nile virus endemic to Oceania.
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Usutu virus (USUV) is a flavivirus belonging to the Japanese encephalitis complex, which is an emerging zoonotic arbovirus of concern because of its pathogenicity to humans and its similarity in ecology with other emerging arboviruses such as West Nile virus. It mainly infects Culex mosquitoes and birds; humans form a dead-end host. First identified in South Africa in 1959, the virus has caused outbreaks in birds across Europe since 1996. Nearly 50 cases in humans have been reported as of 2019, mainly in Europe. These are predominantly asymptomatic, but some people experience neurological symptoms.
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West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family Flaviviridae, from the genus Flavivirus, which also contains the Zika virus, dengue virus, and yellow fever virus. The virus is primarily transmitted by mosquitoes, mostly species of Culex. The primary hosts of WNV are birds, so that the virus remains within a "bird–mosquito–bird" transmission cycle. The virus is genetically related to the Japanese encephalitis family of viruses. Humans and horses both exhibit disease symptoms from the virus, and symptoms rarely occur in other animals.
Climate change in Colorado encompasses the effects of climate change, attributed to man-made increases in atmospheric carbon dioxide, in the U.S. state of Colorado.
The 2017 Uganda Marburg virus outbreak was confirmed by the World Health Organization (WHO) on 20 October 2017 after there had been an initial fatality due to the virus.
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West Nile Fever (WNF) is a mosquito-borne viral infection caused by the West Nile virus (WNV), a member of the Flaviviridae family. The virus primarily incubates in a bird-mosquito transmission cycle, with humans and other mammals serving as incidental hosts.