Which pathogen presents a zoonotic risk?

• A. Trypanosoma brucei
• B. Hymenolepis nana
• C. Toxoplasma gondii
• D. All of the above

Answer: (D)

Zoonotic risk means pathogens that can move from animals to people. In a lab setting, recognizing organisms with this potential helps you implement proper controls to protect personnel.

Trypanosoma brucei is a parasite carried by animals and transmitted through a vector (the tsetse fly). While humans can be affected, animals can serve as reservoirs, so there is a real concern for transmission in environments where animals and vectors are present or where infected animals are handled. That connection to human infection constitutes a zoonotic risk.

Hymenolepis nana, the dwarf tapeworm, has a direct life cycle between humans and rodents. People can become infected by ingesting eggs from contaminated environments, and laboratory rodents can harbor the parasite. This immediate rodent-to-human transmission route makes it a clear zoonotic threat in facilities housing rodents.

Toxoplasma gondii involves cats as the definitive hosts, with humans at risk through contact with cat feces or consumption of undercooked meat containing tissue cysts. In labs, exposure can occur through handling infected animals, litter handling, or contaminated materials, so it presents a recognized zoonotic risk.

Since each of these organisms can be transmitted from animals to humans under certain conditions, all of the above pose zoonotic risks.