What is West Nile Virus?
West Nile virus is a type of virus that is spread to humans through the bite of a mosquito. This virus is covered by a protective “envelope” and carries a single strand of RNA, the genetic material of the virus. It belongs to the Flaviviridae family of viruses, and it is known as an “arbovirus” because it is transported by arthropods, like mosquitoes.
West Nile virus can lead to different health impacts in humans. Some people may not show any symptoms, while others may experience fever and fatigue. In severe cases, the virus can cause serious problems with the nervous system due to inflammation of the brain, known as encephalitis. However, most people who get infected with the West Nile virus do not show any symptoms. Only about 1 out of 4 patients get fever with signs of a viral syndrome, and roughly 1 in 200 people develop serious nerve-related disease.
The West Nile virus, originally from Africa, started to appear in Europe, Asia, and North America in the 1990s. Nowadays, it can be found in many parts of the world.
What Causes West Nile Virus?
The West Nile virus is a disease that people can catch if they’re bitten by a certain type of mosquito, specifically the Culex species. But it’s not just humans who can get this virus – it can also affect animals like birds, horses, dogs, and other mammals. In fact, wild birds can be particularly good at carrying and spreading the virus.
It’s important to note that humans aren’t the primary target of this virus. We call them “accidental dead-end hosts” because the virus doesn’t stay in the human bloodstream for very long and doesn’t reach high levels. Apart from mosquito bites, it’s also possible, although rare, for the West Nile virus to be transmitted through blood or organ donations, breast milk, or from a pregnant mother to her unborn child.
Approximately 1% of people infected with the West Nile virus will experience severe symptoms, and individuals over 50 years old are more likely to develop complications. These complications are mostly related to the nervous system. Additionally, due to the lack of necessary funding, many states are not actively keeping track of the spread of this virus.
Risk Factors and Frequency for West Nile Virus
West Nile virus was first reported in Uganda back in 1937. It caught attention again in 1999 with seven deaths and 62 cases of brain inflammation, or encephalitis, reported in New York. This marked the first appearance of the virus in the western hemisphere. Currently, the virus is found in Africa, Europe, Asia, North America, Australia, and the Middle East.
Initially, the virus caused minor illness. However, by mid-1990s, it became linked with severe neurological diseases such as meningitis and encephalitis. According to a detailed review carried out in 2013, less than one percent of infected patients had these severe conditions, with a mortality rate of 10 percent. West Nile fever can be found in 25% of those infected, while the remaining 75% experience little to no symptoms. This could lead to a huge underreporting of cases. It’s worth noting that outbreaks of the virus are often reported in late summer and fall because of the life cycle of the mosquito that transmits the virus.
- West Nile virus is present in Africa, Europe, Asia, North America, Australia, and the Middle East.
- Initially, it caused minor illnesses, but it has become associated with severe neurological diseases since mid-1990s.
- Less than one percent of infected patients have severe conditions like meningitis and encephalitis, with a death rate of 10 percent.
- About 25% of patients get West Nile fever, while 75% show few to no side effects.
- The virus mostly spreads in late summer and fall thanks to the mosquito’s life-cycle.
From 1999 to 2015, nearly 44,000 confirmed and probable cases of West Nile virus have been reported in the US. This includes over 20,000 cases of severe neurological disease. The number of these severe cases changes dramatically from year to year, ranging from 386 to 2,946. Surveys of the blood of infected patients and blood donors show a severe infection rate of 0.5%, and a total infection rate of 10% in areas where the virus broke out. From this data, we can estimate that there have been between 3 and 5 million cases of West Nile virus infections total.
Signs and Symptoms of West Nile Virus
West Nile virus is a disease that usually shows symptoms within 4 to 14 days after exposure. Most commonly, these symptoms, which can last between 5 to 7 days, can include fever, which is present in at least 25% of patients.
- Feeling of tiredness
- Low-grade fever
- Muscle aches
- Headache
- Eye pain
- Vomiting
- Loss of appetite
- Rash on the trunk of the body
However, in some rare cases, the virus can cause severe neurological symptoms. These may involve serious muscle weakness, changes in mental alertness, seizures, and even sudden loss of muscle function or paralysis. Patients with these serious symptoms often show signs of brain inflammation and/or meningitis, which can progress quickly. Despite intense medical care, the death rate is high in these severe cases.
Most people who get infected with the West Nile virus have recently traveled to an area where the virus is commonly found, mostly in the summer or fall. However, these areas could be in any continent. The usual pattern of the infection includes having a fever that lasts for about five days, headaches for around 10 days, and feeling tired for about a month.
Testing for West Nile Virus
If you’re suspected of having a West Nile virus infection, certain laboratory tests could provide clues. An increase in white blood cells and other non-specific changes could be signs of a viral infection. The main way to diagnose West Nile virus is by testing your blood or cerebrospinal fluid – the clear fluid in and around the brain and spinal cord – for antibodies against the virus. This is done using a method called an enzyme-linked immunosorbent assay, or ELISA, which looks specifically for an antibody called IgM.
Another test called a plaque reduction neutralization test, or PRNT, can help distinguish between reactions to different viruses if there’s any confusion. These lab tests are crucial since having too few sodium ions in your blood (hyponatremia) might also occur when the virus affects the central nervous system.
If the West Nile virus invades the nervous system, a procedure known as a lumbar puncture (or spinal tap) will typically show signs of viral meningitis. This test checks the cerebrospinal fluid for elevated protein and white blood cell levels. You might initially have more neutrophils, a type of white blood cell, but this can shift to an increase in lymphocytes, another type of white blood cell, over time. The levels of glucose in this fluid usually remain normal. If you’re suspected of having the serious, neuroinvasive form of the disease, the cerebrospinal fluid is also checked with the ELISA test. If the first test comes back negative but your doctor still suspects a viral infection, the test may be repeated after 10 days as it takes time for IgM levels to rise to noticeable amounts.
Imaging tests can also be used, but a CT scan of the brain typically won’t show any immediate signs of the disease. An MRI might reveal abnormalities but only several weeks after the neuroinvasive disease begins.
Treatment Options for West Nile Virus
West Nile virus treatment mainly focuses on easing the symptoms. Various potential treatments, including interferon, ribavirin, and an IV treatment with antibodies called immunoglobulin, have been tried. However, it’s not clear how effective these treatments are, as they’ve only been studied in one controlled trial so far.
If a doctor confirms a person has West Nile virus, the treatment will depend on how severe the symptoms are. Those with mild symptoms can often manage their illness at home, and generally, they have a very good chance of recovery. However, people who are seriously ill, especially those suffering from neurological symptoms, may need long-term intensive care. These patients often need physical rehabilitation and occupational therapy due to the extensive recovery period. After recovering from the infection, some individuals may experience motor, thinking, and fine motor abnormalities due to the nerve damage caused by the virus. Some of these neurological deficits may be permanent, and recovery can take a long time.
Since severely affected patients could be bedridden, the risk of bed sores, swallowing difficulties leading to aspiration, and blood clots in their veins, known as deep vein thrombosis (DVT), can be common. Therefore, doctors usually recommend preventive treatments to reduce these risks.
What else can West Nile Virus be?
When a doctor suspects a patient may have the West Nile virus, it’s important to rule out other conditions that may present with similar symptoms. The doctor should start by asking for a detailed travel history, as this can offer clues as to what the patient could potentially have contracted. Here are some other conditions that they may consider:
- Bacterial meningitis
- Varicella-zoster virus
- Herpes simplex type 1 virus
- St. Louis encephalitis (confirmatory testing is needed since it may cross-react)
- Enteroviruses
- Dengue virus
- Japanese encephalitis
Additionally, the doctor will also consider illnesses that are transmitted by ticks:
- Lyme disease
- Ehrlichiosis
- Anaplasmosis
- Rocky Mountain spotted fever
- Powassan virus
What to expect with West Nile Virus
The majority of people with West Nile virus (WNV) will recover well. Most people who are infected don’t even experience symptoms. Those who do get sick, usually experience symptoms similar to a common viral infection, and recover within about 10 days.
However, a small percentage of cases can develop into a more serious condition known as neuroinvasive disease, which can affect the nervous system causing various neurologic problems. This more severe form of the disease carries a mortality rate of around 10 percent, and older people are the most susceptible. Some of the neurologic issues caused by this disease may last for years or could even be permanent.
The most severe forms of the disease are most common among the elderly, and the highest risk factor for death is if the disease affects the nervous system. In such cases, between 1-4% of patients may pass away.
Possible Complications When Diagnosed with West Nile Virus
Symptoms can vary greatly with different conditions, and can even affect various parts of the body. Here are a few related symptoms:
- Neurological symptoms – This can involve conditions like meningitis, encephalitis or weakness. In severe cases, it could include acute flaccid paralysis, seizures, or even coma.
- Ocular manifestations – This means symptoms affecting your eyes, such as vitreitis, chorioretinitis, or retinal hemorrhages.
- Myocarditis – This is a condition causing inflammation in the heart.
- Pancreatitis – Pancreatitis is a condition causing inflammation in the pancreas.
- Rhabdomyolysis – This condition causes a breakdown of muscle tissue that leads to the release of muscle fiber contents into the blood.
- Central diabetes insipidus – This is a condition where the body can’t balance water in the urine, leading to excessive urination and thirst.
- Death – In severe cases, these conditions can unfortunately lead to death.
Preventing West Nile Virus
The West Nile Virus (WNV) is mainly spread through mosquito bites. So, the best way to prevent it is by avoiding mosquito bites. There are two main ways to do this: personal protective measures and mosquito control.
Personal protective measures include using insect repellents that contain DEET or picaridin, wearing clothes treated with permethrin (a insecticide), and avoiding areas where there’s a high risk of getting bitten by mosquitoes, like places where mosquitoes are very common.
Mosquito control programs can also help reduce the risk of exposure to WNV. These programs aim to decrease the number of mosquitoes, especially in high-risk areas. Another effective method is to eliminate conditions that attract mosquitoes, like standing water around your house.
