Objective: Herein we investigated the neuropathogenic outcomes and underlying mechanisms of dual lentivirus infections with genetically distinct viral strains as co-infections or super-infections. Design: Experimental Feline Immunodeficiency Virus (FIV) infections were performed using cultured feline cells and an in vivo model of AIDS neuropathogenesis. Methods: Dual infections were carried out with two FIV strains (FIV-Ch and FIV-PPR) as co-passaged or superinfected viruses ex vivo in feline monocytederived- macrophages and in vivo in an established feline model with subsequent analyses of outcomes using real time RT-PCR, neuropathological features, quantitation of viral load and measures of neurobehavioral performance. Results: Dual infections caused greater IL-1beta, TNFalpha and IDO expression and neurotoxic properties in infected feline macrophages. Co-infection and sequential FIV super-infection in vivo also induced greater IL-1beta, TNFalpha and IDO expression in the basal ganglia (BG) and frontal cortex (CTX), compared to the mono- and mock-infection groups, although viral loads were similar in mono- and dual-infected animals. Immunoblot analyses disclosed lower synaptophysin immunoreactivity resulting from FIV superinfection and co-infection in the CTX. Both cholinergic and GABAergic neuronal injury were evident in the in CTX of animals with dual FIV infection. With increased astrocytic and microglial activation and neuronal loss in dual FIV-infected brains, immunohistochemical analysis also revealed elevated detection of cleaved caspase-3, concurrent with dysmorphic changes in neurons and associated neurobehavioural abnormalities. Conclusions: These findings highlight the adverse biological effects of dual lentivirus infections in super-infection and co-infection models for which the underlying pathogenic mechanisms represent an escalation in neuroinflammation and ensuing neurodegeneration.

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