Pandemic swine-origin H1N1 influenza A virus isolates show heterogeneous virulence in macaques.

The first influenza pandemic of the new millennium was caused by a newly emerged swine-origin influenza virus (SOIV) (H1N1). This new virus is characterized by a previously unknown constellation of gene segments derived from North American and Eurasian swine lineages and the absence of common markers predictive of human adaptation. Overall, human infections appeared to be mild, but an alarming number of young individuals presented with symptoms atypical for seasonal influenza. The new SOIV also showed a sustained human-to-human transmissibility and higher reproduction ratio than common seasonal viruses, altogether indicating a higher pathogenic potential for this newly emerged virus. To study the virulence of the SOIV, we used a recently established cynomolgus macaque model and compared parameters of clinical disease, virology, host responses, and pathology/histopathology with a current seasonal H1N1 virus. We here show that infection of macaques with two genetically similar but clinically distinct SOIV isolates from the early stage of the pandemic (A/Mexico/4108/2009 and A/Mexico/InDRE4487/2009) resulted in upper and lower respiratory tract infections and clinical disease ranging from mild to severe pneumonia that was clearly advanced over the mild infection caused by A/Kawasaki/UTK-4/2009, a current seasonal strain. Unexpectedly, we observed heterogeneity among the two SOIV isolates in virus replication, host transcriptional and cytokine responses, and disease progression, demonstrating a higher pathogenic potential for A/Mexico/InDRE4487/2009. Differences in virulence may explain more severe disease, as was seen with certain individuals infected with the emerged pandemic influenza virus. Thus, the nonhuman primate model closely mimics influenza in humans.

Host response dynamics following lethal infection of rhesus macaques with Zaire ebolavirus.

To gain further insight into the interdependent pathogenic processes in Ebola hemorrhagic fever (EHF), we have examined the dynamics of host responses in individual rhesus macaques infected with Zaire ebolavirus over the entire disease course. Examination of coagulation parameters revealed that decreased coagulation inhibitor activity triggered severe coagulopathy as indicated by prolonged coagulation times and decreased fibrinogen levels. This has been proposed as one of the significant mechanisms underlying disseminated intravascular coagulation in EHF patients. Furthermore, monitoring of expression levels for cytokines/chemokines suggested a mixed anti-inflammatory response syndrome (MARS), which indicates that a catastrophic uncontrolled immunological status contributes to the development of fatal hemorrhagic fever. These results highlight the pathological analogies between EHF and severe sepsis and not only contribute to our understanding of the pathogenic process, but will also help to establish novel postexposure treatment modalities.

Establishment of a Genetically Confirmed Breeding Colony of Mastomys natalensis from Wild-Caught Founders from West Africa.

Mastomys natalensis are a ubiquitous and often dominant rodent across sub-Saharan Africa. Importantly, they are a natural reservoir for microbial pathogens including Lassa virus (LASV), the etiological agent of Lassa fever in humans. Lassa-infected rodents have been documented across West Africa and coincide with regions where annual outbreaks occur. Zoonotic transmission to humans most often occurs directly from infected rodents. Little is known about LASV infection kinetics and transmissibility in M.natalensis, primarily due to available animals. Here, we describe the establishment of a laboratory breeding colony of genetically confirmed M.natalensis from wild-captured rodents. This colony will provide a convenient source of animals to study LASV and other emerging pathogens that utilize M. natalensis in their enzootic lifecycles.

Effects of acute and chronic murine norovirus infections on immune responses and recovery from Friend retrovirus infection.

Murine norovirus (MNV) is a highly infectious but generally nonpathogenic agent that is commonly found in research mouse colonies in both North America and Europe. In the present study, the effects of acute and chronic infections with MNV on immune responses and recovery from concurrent Friend virus (FV) infections were investigated. No significant differences in T-cell or NK-cell responses, FV-neutralizing antibody responses, or long-term recovery from FV infection were observed. We conclude that concurrent MNV infections had no major impacts on FV infections.

Role of Erk1/2 activation in prion disease pathogenesis: absence of CCR1 leads to increased Erk1/2 activation and accelerated disease progression.

Prion diseases are neurodegenerative infections with gliosis and vacuolation. The mechanisms of degeneration remain unclear, but chemokines may be important. In current experiments CCR1 knock-out (KO) mice succumbed more rapidly to scrapie infection than WT controls. Infected KO mice had upregulation of CCL3, a CCR1 ligand, and CCR5, a receptor with specificity for CCL3. Both infected KO and WT mice had upregulation of CCR5-mediated signaling involving activation of Erk1/2 in astrocytes; however, activation was earlier in KO mice suggesting a role in pathogenesis. In both mouse strains activation of the Erk1/2 pathway may lead to astrocyte dysfunction resulting in neurodegeneration.

Seasonal H3N2 influenza A virus fails to enhance Staphylococcus aureus co-infection in a non-human primate respiratory tract infection model.

Staphylococcus aureus community-acquired pneumonia is often associated with influenza or an influenza-like syndrome. Morbidity and mortality due to methicillin-resistant S. aureus (MRSA) or influenza and pneumonia, which includes bacterial co-infection, are among the top causes of death by infectious diseases in the United States. We developed a non-lethal influenza A virus (IAV) (H3N2)/S. aureus co-infection model in cynomolgus macaques (Macaca fascicularis) to test the hypothesis that seasonal IAV infection predisposes non-human primates to severe S. aureus pneumonia. Infection and disease progression were monitored by clinical assessment of animal health; analysis of blood chemistry, nasal swabs, and X-rays; and gross pathology and histopathology of lungs from infected animals. Seasonal IAV infection in healthy cynomolgus macaques caused mild pneumonia, but unexpectedly, did not predispose these animals to subsequent severe infection with the community-associated MRSA clone USA300. We conclude that in our co-infection model, seasonal IAV infection alone is not sufficient to promote severe S. aureus pneumonia in otherwise healthy non-human primates. The implication of these findings is that comorbidity factors in addition to IAV infection are required to predispose individuals to secondary S. aureus pneumonia.

The M-PMV cytoplasmic targeting-retention signal directs nascent Gag polypeptides to a pericentriolar region of the cell.

Intracytoplasmic protein targeting in mammalian cells is critical for organelle function as well as virus assembly, but the signals that mediate it are poorly defined. We show here that Mason-Pfizer monkey virus specifically targets Gag precursor proteins to the pericentriolar region of the cytoplasm in a microtubule dependent process through interactions between a short peptide signal, known as the cytoplasmic targeting-retention signal, and the dynein/dynactin motor complex. The Gag molecules are concentrated in pericentriolar microdomains, where they assemble to form immature capsids. Depletion of Gag from this region by cycloheximide treatment, coupled with the presence of ribosomal clusters that are in close vicinity to the assembling capsids, suggests that the dominant N-terminal cytoplasmic targeting-retention signal functions in a cotranslational manner. Transport of the capsids out of the pericentriolar assembly site requires the env-gene product, and a functional vesicular transport system. A single point mutation that renders the cytoplasmic targeting-retention signal defective abrogates pericentriolar targeting of Gag molecules. Thus the previously defined cytoplasmic targeting-retention signal appears to act as a cotranslational intracellular targeting signal that concentrates Gag proteins at the centriole for assembly of capsids.