The virus has a neurologic component, and most cases of neurologic disease are severe and occur in elderly patients and/or diabetics. These neuroinvasive cases—characterized by central nervous system involvement, severe headache, nausea, and vomiting—tend to be the ones in which there are ocular manifestations.
The typical presentations in symptomatic patients—who account for about 15% of affected patients with West Nile virus—are systemic in nature (i.e., fever, headache, myalgia, arthralgia, nausea, vomiting, skin rash, and pharyngitis). The virus generally has incubation periods ranging from 2 to 14 days and the fever is self-limited and lasts about 1 week.
Most patients (80%) are asymptomatic. At the other end of the spectrum are 5% of patients with encephalitis who have severe headaches, meningismus, confusion, stupor/coma, tremors, convulsions, and paralysis.
Ocular manifestations can vary among patients and included anterior chamber and vitreous inflammation, retinal vasculitis, retinitis, choroiditis (the most common finding), and multifocal chorioretinitis in a curvilinear pattern. The early retinal lesions are deep yellow-white. Fluorescein and indocyanine green angiography (ICGA) are valuable for identifying these lesions.
Dengue fever is similar to West Nile virus in that it also is a flavivirus, about the same size as West Nile virus at 11 kilodaltons, the incubation periods range from 2 to 14 days, and the disease has a worldwide distribution.
A difference is that Dengue fever tends to be limited to tropical environs, where it is endemic and occurs less often than West Nile virus. An estimate is that 50 to 100 million new cases develop each year. Cases do appear in the United States, largely in Florida and Texas, and these represent most of the cases. However, some are imported, i.e., acquired during travel, Dr. Cunningham explained.
Patients with Dengue fever also are affected systemically.