You might not expect someone with those credentials to take zombies seriously, but it turns out the undead are a great way to explore real-world health issues: why certain nasty diseases can destroy the brain, how global pandemics create chaos and fear, and what should be done about people infected with a highly contagious and incurable lethal illness

Virus already exists
An extreme behavior change could drive a person mad. One might even desire to attack others on site. This would benefit the virus by allowing it to spread through a bit from the infected organize to the victim. It’s understandable that because they don’t have control of their desires and motives the infected would loose their gift of freewill in other words a form of zombification. Viruses have the devastating ability to spread very rapidly and can easily cause a human epidemic or a zombie apocalypse .

Church Camping Trip Leads to Teens Needing Rabies Shots

"She finds herself a good one (cockroach), she stings it — and the sting paralyzes it for a minute — and she's able to get her stinger right inside the brain of the roach, that actually disables it from any instincts to run away," Stewart says. "It makes it this very docile, obedient cockroach." The wasp is then able to lead the cockroach around and place it wherever she'd like it to be before laying her eggs in the cockroach's belly. After the larvae hatch, they eat the roach's interior organs and use its outer shell as a protective exterior.

"Zombie Virus" Possible via Rabies-Flu Hybrid?
Highly improbable genetic tweak could create mutant virus.

To date, H5N1 remains mainly a virus affecting birds, although it has killed more than 200 people since 2003. But scientists say it is the most likely source of the next deadly flu pandemic in humans, since it may soon mutate into a form transmitted easily from person to person.

Avian Influenza A Virus Infections of Humans

Toxoplasmosis is found in humans worldwide, and in many species of animals and birds. Cats are the definitive host of the parasite. Human infection may result from: Blood transfusions or solid organ transplants Carelessly handling cat litter, which can lead to accidental consumption of infectious particles Eating contaminated soil Eating raw or undercooked meat (lamb, pork, and beef) Toxoplasmosis also affects people who have weakened immune systems. The infection may also be passed from an infected mother to her baby through the placenta. See: Congenital toxoplasmosis

Possible link to psychiatric disorders Studies have been conducted that show the toxoplasmosis parasite may affect behavior and may present as or be a causative or contributory factor in various psychiatric disorders such as depression, anxiety and schizophrenia.[9][10][11] In 11 of 19 scientific studies, T. gondii antibody levels were found to be significantly higher in individuals affected by first-incidence schizophrenia than in unaffected persons. Individuals with schizophrenia are also more likely to report a clinical history of toxoplasmosis than those in the general population.[12] Recent work at the University of Leeds has found that the parasite produces an enzyme with tyrosine hydroxylase and phenylalanine hydroxylase activity. This enzyme may contribute to the behavioral changes observed in toxoplasmosis by altering the production of dopamine, a neurotransmitter involved in mood, sociability, attention, motivation and sleep patterns. Schizophrenia has long been linked to dopamine dysregulation.[13]