West Nile Virus (WNV) is an RNA virus belonging to the Japanese encephalitis family. It is a flavivirus, like Dengue and Zika. It is transmitted by mosquitos. WNV first appeared in North America in 1999. It has subsequently spread throughout the continental United States, where it has flourished. The 2003 US epidemic was the largest WNV outbreak ever reported. In the US, less than 3% of the population has antibodies, suggesting that WNV could continue to cause large epidemics. Fortunately however, it appears to have greatly reduced in recent years (e.g. 2018 in Chicago Illinois).
WNV is harbored in both mosquito's and birds. A sudden die-off in bird populations, such as crows, sometimes precede a subsequent human epidemic. Such a die-off occurred in Chicago. WNV is not common in animals -- but horses can also become infected. WNV can be also be transmitted from breast milk.
There are two related flaviviruses, that may be associated with dizziness as well, Dengue and Zika. Zika virus received its name from the Zika forest in Uganda. There recently has been an outbreak in South America in Brazil (Smith et al, 2016). Zika is transmitted through mosquito bites, as well as through sexual intercourse, and likely also through blood. The majority of infections are likely asymptomatic. Zika is associated with microcephalis in infants. Zika diagnosis relies on RT-PCR of bodily fluids, such as serum, urine, or CSF.
About 80% of WNV virus infections are asymtomatic. 20% develop West Nile Fever (WNF), and less than 1% develop West Nile Neuroinvasive Disease (WNND).
In WNF, persons develop fever, headache, fatigue and a generalized rash. headache typically lasts for 10 days, weakness for 1 month, and fever for about 1 week.
In WNND, patients may develop meningitis, encephalitis, and a polio like syndrome. About 40% have meningitis, and 60% encephalitis.
Cranial nerve palsies are common in WNND. The 7th cranial nerve (causing Bell's palsy) is the most commonly affected. Next most common is the 8th cranial nerve, which may account for dizziness, vertigo and nystagmus. (Parrino et al, 2019)
Video of opsoclonus in young woman, developed after the West Nile outbreak in Chicago.
See the Movie page for a list of more movies like this one.
Opsoclonus-myoclonus (see also this link) is thought to be unusual in WNND but it has been reported over and over in the literature (Sayao, Suchowersky et al. 2004; Khosla, Edelman et al. 2005; Alshekhlee, Sultan et al. 2006; Joyner, Kelly et al. 2006; Prasad, Brown et al. 2006; Wong 2007, Afzal et al, 2014; Cooper 2014; Birlutiu 2014). The author saw a huge surge in cases of ocular flutter and opsoclonus in his clinical practice, after WNV became prevalent in Chicago. In 2006, about 20% of the mosquito's on the Chicago South Side carried WNV. All of these patients seen by the author during this time had developed flutter or opsclonus accompanied by headache and ataxia. It is the author's opinion that West Nile may be a common cause of opsoclonus, at least in parts of the country where WNV is common.
Other flaviviruses related to WNV with dizziness.
The author of this page has encountered a small number of patients (out of an 'n' of about 25,000 dizzy patients), who had Dengue virus exposure documented prior to developing dizziness. Of two Dengue patients, one had a bug bite on the ear that subsequently developed vestibular neuritis. In another, a dengue virus conversion was documented roughly at the same time as the individual developed dizziness with a "quick spin" time frame, suggestive of vestibular paroxysmia.
Regarding Zika, the author has encountered a single young person who spent 3 months in Brazil, came back, and then developed bilateral vestibular loss. The connection here between Zika and the bilateral loss is admittedly tenuous. Still, the them is that these viruses may be another source of vestibular nerve damage. It is to be expected that as technology for detecting vestibular nerve damage improves (i.e. the VHIT test), we will see more of these situations.
General laboratory testing simply indicates that the patient is ill, but is not at all specific for WNV.
Spinal fluid, which must be abnormal to make a diagnosis of WNND anyway, is generally very abnormal in WNND in a nonspecific way with increased inflammatory cells and protein. The specific identification of WNV is generally basied on detection of specific antibodies to WNV in serum or CSF. The cumulative percentage of patients who are seropositive increases by about 10% per day during the first week.
Because the diagnosis of WNV is based on antibody testing, and a "gold standard" is lacking, false-negatives could be common. We have never encountered anyone with serum antibodies to WNV, and we think that this is a very low yield diagnostic test.
Neuroimaging studies are often normal in WNV, with DWI (diffusion weighted MRI) being the most sensitive modality. DWI doesn't diagnose WNV, but it may show where the worst brain damage is located. In our clinical practice in Chicago, we had a patient present with dural enhancement.
There is currently (2019) no treatment proven effective in WNV.
Patients with WNND generally take months or even years to recover. In the NY outbreak of 1999, only 37% of infected patients felt that they were fully recovered at 1 year post onset. WNV persists in the brains of infected monkeys for 5-6 months after resolution of their clinical illness, and the prolonged course may be in part related to persistent virus.
Prevention of WNV requires prevention of mosquito bites, and eradication of mosquitos. In spite of considerable publicity about WNV, and even a 20% infection rate of mosquito's in certain parts of Chicago, utilization of mosquito repellant and mosquito abatement has not been commonly adopted.