Associate Professor - Veterinary and Biomedical Sciences

Research Interests
Dr Njenga’s overall major research interests are in virus pathogenesis and virus-immune interactions, which are investigated using two picornaviral models. Research on xenotransplantation (use of animal cells, tissues, or organs to treat human diseases) as a means of overcoming the acute shortage of tissues and organs for transplanting into humans is focused on the use of pigs as donor animals, in part because pigs are readily available, easy to breed, and they have similar anatomical and physiological features as humans. However, a major concern is that xenografts may transmit undetected viruses from pigs to humans or that human viruses present in the recipient may infect the xenograft and render it useless. Our laboratory has developed an encephalomyocarditis virus (EMCV) model for graft-to-recipient (pig-to-mouse or pig-to-monkey) xenozoonosis. We demonstrated that an EMCV strain isolated from naturally infected pigs persisted in pig cardiomyocytes and central nervous system cells, associated with extensive apoptosis and viral antigen expression. Apart from pigs, EMCV-30 also caused severe disease in cynomolgus macaques and mice, and productively infected primary human cardiomyocytes, suggesting that it is a potential zoonotic agent. Transplantation of EMCV-infected porcine islet cells (PICs), which are already in clinical trial for treatment of type I diabetes in humans, into diabetic mice cured the diabetes but it also resulted in transmission of the virus and the viral disease to the recipient. Presently, we are investigating the effects of viral infection on performance of PICs, and determining the change in disease pathogenesis as a result of transplantation-associated physiological and immunological changes. We also use a picornaviral model of human multiple sclerosis (MS) disease to investigate the role of immune responses in the myelin destructive processes in the central nervous system. Human male MS patients develop more severe clinical symptoms and deteriorate faster after contracting the disease, and the biological basis and the underlying physiological and biochemical mechanisms for this dimorphism are poorly understood. We are using our well-characterized picornaviral model of demyelination, whose disease paradigm (males vs females) is similar to human disease, to investigate the interaction between sex hormones, the immune system, and neurological disabilities.

Selected Publications
(For a comprehensive list of  Dr. Njenga's recent publications, refer to PubMed, a service provided by the National Library of Medicine.)

Brewer, L., Lwamba, H.C.M., Murtaugh, M.P., Brown, C., Palmenberg, A.C., Njenga, M.K. Porcine encephalomyocarditis virus persists in pig myocardium and infects human myocardial cells. J. Virol. 11621-11629, 2001.

LaRue, R., Brewer, L., Brown, C., Njenga, M.K. A wildtype porcine encephalomyocarditis virus containing a short poly(C) tract is pathogenic to mice, pigs, and cynomolgus macaques. J Virol. 77:9136-9146, 2003.

Brewer, L.A., Brown, C., Murtaugh, M.P., Njenga, M.K. Transmission of encephalomyocarditis virus (EMCV) to immunodeficient mice by transplanting tissues from EMCV-infected pigs. Xenotransplantation (In Press).

Johnson, A.J., Njenga, M.K., Hansen, M.J., Kuhns, S.T., Chen, L., Rodriguez, M., Pease, L.R. Prevalent Class I-restricted T-cell response to the Theiler's virus epitope Db:VP2_121-130 in the absence of endogenous CD4 help, tumor necrosis factor alpha, gamma interferon, perforin, or costimulation through CD28. J. Virol. 73: 3702-3708, 1999.

Alley, J., Khasabov, S., Simone, D., Beitz, A., Rodriguez, M., Njenga, M.K. More severe neurologic deficits in SJL/J male than female mice following Theiler’s virus-induced CNS demyelination. Experimental Neurol 180:14-24, 2003.

Shin, H-J., Cameron, K.T., Jacobs, J.A., Turpin, E.A., Halvorson, D.A., Goyal, S.M., Nagaraja, K.V., Kumar, M.C., Lauer, D.A., Seal, B.S., Njenga, M.K. Molecular epidemiology of subgroup C avian pneumoviruses isolated from the United States and comparison with subgroup A and B viruses. J. Clin. Microbiol. 40:1687-1693, 2002.

Current Funding
"Risk of Porcine Picornavirus in Xenotransplantation," NIH.

"Development of Reverse Genetics Rescue System for Avian Pneumovirus," NRICGP-USDA.

"Full genome sequencing of Avian Pnuemovirus," U of M Agricultural Experiment Station.

Honors and Awards
Bosworth Grier Outstanding Graduate Student, Pennsylvania State University, 1994.

National Institutes of Health Postdoctoral Fellow, 1997–1999.

Outstanding Research Fellow, Neurology Department, Mayo Clinic and Foundation, 1999.

Adjunct Visiting Scientist, Mayo Clinic and Foundation, 1999–present.

Current Students
Jessica Lynch, Ph.D. in Neuroscience, Spring 2006.