Marina Siirin

Persistent West Nile Virus Infection in the Golden Hamster: Studies on Its Mechanism and Possible Implications for Other Flavivirus Infections

Golden hamsters (Mesocricetus auratus) experimentally infected with West Nile virus (WNV) developed chronic renal infection and persistent shedding of virus in urine for up to 8 months, despite initial rapid clearance of virus from blood and the timely appearance of high levels of specific neutralizing antibodies. Infectious WNV could be recovered by direct culture of their urine and by cocultivation of kidney tissue for up to 247 days after initial infection. Only moderate histopathologic changes were observed in the kidneys or brain of the chronically infected hamsters, although WNV antigen was readily detected by immunohistochemistry within epithelium, interstitial cells, and macrophages in the distal renal tubules. Comparison of WNV isolates from serial urine samples from individual hamsters over several months indicated that the virus underwent both genetic and phenotypic changes during persistent infection. These findings are similar to previous reports of persistent infection with tickborne encephalitis and Modoc viruses.

Year-round West Nile virus activity, Gulf Coast Region, Texas and Louisiana

West Nile virus (WNV) was detected in 11 dead birds and two mosquito pools collected in east Texas and southern Louisiana during surveillance studies in the winter of 2003 to 2004. These findings suggest that WNV is active throughout the year in this region of the United States.

Experimental infection of ground squirrels (Spermophilus tridecemlineatus) with monkeypox virus.

A new, small-animal model of severe orthopoxvirus infection (monkeypox) is described.

Human outbreak of St. Louis encephalitis detected in Argentina, 2005

BACKGROUND An outbreak of flavivirus encephalitis occurred in 2005 in Córdoba province, Argentina. OBJECTIVES To characterize the epidemiologic and clinical features of that outbreak and provide the serologic results that identified St. Louis encephalitis virus (SLEV) as the etiologic agent. STUDY DESIGN From January to May 2005, patients with symptoms of encephalitis, meningitis, or fever with severe headache were evaluated and an etiologic diagnosis achieved by detection of flavivirus-specific antibody sera and cerebrospinal fluid. RESULTS The epidemic curve of 47 cases showed an explosive outbreak starting in January 2005 with one peak in mid-February and a second peak in mid-March; the epidemic ended in May. Cases occurred predominantly among persons 60 years and older. Nine deaths were reported. SLEV antibodies, when detected in 47 patients studied, had a pattern characteristic of a primary SLEV infection. CONCLUSIONS Even though isolated cases of St. Louis encephalitis have been reported in Argentina, this is the first description of a large SLEV encephalitis outbreak in Argentina.

Experimental infection of prairie dogs with monkeypox virus.

Infected prairie dogs can transmit monkeypox virus by respiratory and mucocutaneous contact with susceptible animals and humans.

Rabies vaccine preserved by vaporization is thermostable and immunogenic.

A rabies vaccine that is thermostable over a range of ambient environmental temperatures would be highly advantageous, especially for tropical regions with challenging cold-chain storage where canine rabies remains enzootic resulting in preventable human mortality. Live attenuated rabies virus (RABV) strain ERAG333 (R333E) was preserved by vaporization (PBV) in a dry, stable foam. RABV stabilized using this process remains viable for at least 23 months at 22°C, 15 months at 37°C, and 3h at 80°C. An antigen capture assay revealed RABV PBV inactivated by irradiation contained similar levels of antigen as a commercial vaccine. Viability and antigen capture testing confirmed that the PBV process stabilized RABV with no significant loss in titer or antigen content. Live attenuated and inactivated RABV PBV both effectively induced RABV neutralizing antibodies and protected mice from peripheral RABV challenge. These results demonstrate that PBV is an efficient method for RABV stabilization.