Acute infection of humans with Ebola and Lassa viruses, two principal etiologic agents of hemorrhagic fevers, often results in a paradoxical pattern of immune responses: early infection, characterized by an outpouring of inflammatory mediators such as TNF-α, IL-1β, and IL-6, vs late stage infections, which are associated with poor immune responses. The mechanisms underlying these diverse outcomes are poorly understood. In particular, the role played by cells of the innate immune system, such as dendritic cells (DC), is not known. In this study, we show that Ebola and Lassa viruses infect human monocyte-derived DC and impair their function. Monocyte-derived DC exposed to either virus fail to secrete proinflammatory cytokines, do not up-regulate costimulatory molecules, and are poor stimulators of T cells. These data represent the first evidence for a mechanism by which Ebola and Lassa viruses target DC to impair adaptive immunity.

The size and duration of the 2000 outbreak of Sudan Ebola virus (SEBOV) infection in Uganda made it possible to collect serial serum samples from 87 patients (53 survivors and 34 nonsurvivors). Surprisingly, the levels of tumor necrosis factor- alpha and interferon (IFN)- gamma , which had been found to be increased in patients with fatal Zaire Ebola virus infection, were not increased in any of the patients with SEBOV infection. The levels of interleukin (IL)-1 beta , IFN- gamma -inducible protein-10, and RANTES (regulated on activation, normally T cell-expressed and -secreted) were higher in samples from all patients with SEBOV infection than in control samples from healthy hospital staff members, but their levels did not differ between those who survived and those who did not. The levels of IFN- alpha were significantly higher in surviving patients with SEBOV infection, whereas the levels of IL-6, IL-8, IL-10, and macrophage inflammatory protein-1 beta were higher in patients with fatal SEBOV infections.

This report describes the first detailed analysis of the replication, persistence, and excretion of a North American hantavirus in its natural rodent reservoir. Black Creek Canal virus was isolated from Sigmodon hispidus (cotton rat) shortly after the identification of a hantavirus pulmonary syndrome (HPS) case occurring in southern Florida. Six-week-old male cotton rats were inoculated subcutaneously with 1,000 tissue culture infectious doses. Viral complementary RNA (vcRNA) was quantified as a means of determining the site(s) of viral activity (transcription and replication). In the first few weeks post inoculation (pi), vcRNA was detectable in every tissue examined except blood. The quantities of vcRNA decreased over time, and by five months pi it could be detected only in the brain. In addition to using a quantitative polymerase chain reaction (QPCR) as a means of measuring viral replication/ transcription, attempts were made to reisolate virus from all tissue samples taken. Virus could be isolated from every solid tissue examined, and the titers appeared to decrease over time, similar to the QPCR results. However, in contrast to the QPCR results, infectious virus was still routinely detectable at low levels in adrenal gland, liver, kidney, and testicle 150 days pi. Although results of testing for vcRNA in the blood were uniformly negative, infectious virus was detected at one week pi, reached highest titers at two weeks, and decreased dramatically by three weeks. After three weeks pi, infectious virus could only be detected sporadically in blood. Virus was isolated from urine collected during the first 70 days pi and throughout the entire study period in feces and wet bedding. These data indicate that the viral infection can be separated into an acute phase associated with high virus titers, and a chronic or persistent phase associated with lower virus titers and continued shedding of virus in excreta.

Sin Nombre (SN) virus is the major etiologic agent of hantavirus pulmonary syndrome, a severe respiratory disease with high mortality. Like other hantaviruses, SN virus causes an inapparent chronic infection of the natural rodent reservoir and tends to grow slowly and produce little cytopathic effect even in highly susceptible Vero E6 tissue culture cells. An electrochemiluminescent quantitative PCR approach was developed to allow examination of SN virus RNA transcription in synchronously infected cells. Although virion particles contain equimolar ratios of the three negative-strand genome RNA segments (S, M, and L), rates and levels of accumulation of the corresponding N, GPC, and L viral mRNAs varied. The smallest mRNA (N) was detectable earliest and plateaued at the highest level, where as the largest mRNA (L) appeared latest and at the lowest plateau level. In addition, all three mRNAs were found to share a common 5' capped primer initiation mechanism, but appeared to have different mRNA termination mechanisms. The N mRNA 3' terminus mapped to position 1435 on the S segment, in close proximity to a CCC-rich suspected transcription termination motif. The GPC mRNA 3' terminus contained a poly(A) tall and mapped to a U8 transcription termination-polyadenylation motif reminiscent of those seen in other negative-strand RNA viruses. Finally, the L mRNA 3' terminus appeared identical to the L segment antigenome 3' terminus.