Whitewater: It Just Won’t Go Away!

Special report

Synopsis: The first human infections caused by Whitewater Arroyo virus, an arenavirus, have been detected in California.

On aug. 4, 2000, it was announced that the first three human cases of New World arenavirus infection in North America, all fatal, had been detected. Each case occurred in a different area of California and each involved a female. A 14-year-old resident of both Riverside and Los Angeles counties was the first case, followed by a 30-year-old resident of Alameda county in February 2000, and, in May 2000, by a 52-year-old resident of Orange County. Each patient initially developed an influenza-like illness with high fever, lymphocytopenia, and progression to respiratory distress requiring mechanical ventilation. Two of the three also developed hepatitis and hemorrhagic manifestations.

Examination of tissue specimens by nested reverse polymerase chain reaction (PCR), performed at the University of Texas in Austin, yielded amplification products found to be consistent with Whitewater Arroyo (WWA) virus.

Comment by Stan Deresinski, MD, FACP

The arenaviruses derive their designation from the Latin word arenosus, meaning "sandy"—a description of the appearance of host cell ribosomes as 20-25 nM electron dense granules within the viral particle. This group of negative-stranded RNA viruses primarily affects rodents, which can become chronically infected and serve as the reservoir of infection. Humans are accidental hosts who become infected as the result of contact with rodent excreta.

Arenaviruses previously known to have affected humans include lymphocytic choriomeningitis virus (LCM), Lassa fever virus, and the viruses that cause the South American hemorrhagic fevers—Junin (Argentine), Machupo (Bolivian), Guanarito (Venezuelan), and Sabia (Brazilian). Lassa fever virus and LCM virus are the known human pathogens among the Old World arenaviruses, while the South American hemorrhagic fever viruses and, now, WWA virus are the only New World (also known as Tacaribe complex) arenaviruses known to cause disease in humans. The only known New World arenavirus in North America besides WWA virus is the Tamiami virus (named after the Tamiami trail in south Florida), which has only been detected in rodents.

WWA virus was first isolated from white-throated wood rats (Neotoma albigula) recovered in the Whitewater Arroyo in McKinley County, New Mexico.1 White-throated woodrats are found in other areas of the southwestern United States, extending from California to the central plateau of Mexico, to west Texas, and north to Utah and Colorado, including Texas and California, and its habitat is predominantly desert-like. They are often commonly referred to as "pack rats" and are nocturnal.

Treatment with ribavirin has been suggested to provide clinical benefit to patients with some other arenavirus infections, as well as in hantavirus infection. Whether it has activity against WWA virus is, as yet, unknown.

Reference

1. Fulhorst CF, et al. Isolation and characterization of Whitewater Arroyo virus, a novel North American arenavirus. Virology 1996;224:114-120.