Microbiology Terms Starting With Z
Microbiology Glossary: Z
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Zooflagellate
/ ZOH-oh-FLAJ-uh-layt / · From Greek zoon meaning animal and Latin flagellum meaning whip, referring to animal-like protists with whip-like appendages
Zooflagellate is a heterotrophic, single-celled eukaryote that bears one or more flagella used for locomotion and feeding, lacks chloroplasts, and obtains nutrition by ingesting organic matter or living as a parasite.
Zooflagellates are not a single evolutionary lineage but a functional grouping of flagellated protists that share a heterotrophic lifestyle. Most species possess one to eight flagella that rotate or undulate to propel the cell through aquatic or host environments at speeds reaching 200 micrometers per second. Trypanosoma brucei, the agent of African sleeping sickness, and Trypanosoma cruzi, which causes Chagas disease, together affect more than 20 million people worldwide and exemplify the parasitic zooflagellate lifestyle.
Free-living zooflagellates in soil and freshwater consume bacteria at rates that significantly accelerate nitrogen and phosphorus cycling, linking microbial biomass to higher trophic levels. Termite gut symbionts such as Trichonympha species digest cellulose on behalf of their hosts, and these protists can account for up to one-third of a termite’s body weight.
Mixotricha paradoxa, a zooflagellate living in the gut of Australian termites (Mastotermes darwiniensis), does not move primarily using its own flagella. Locomotion is driven by roughly 250,000 spirochete bacteria attached to its surface, making it one of the most unusual examples of a eukaryote outsourcing motility to symbiotic prokaryotes.
All flagellated protists are zooflagellates. Euglenoids and dinoflagellates bear flagella but possess chloroplasts and are classified as phytoflagellates; some can switch between photosynthetic and heterotrophic nutrition depending on light availability.
Giardia lamblia, a zooflagellate with four pairs of flagella, attaches to the lining of the human small intestine using a ventral adhesive disk and causes giardiasis in an estimated 280 million people each year. The parasite completes its life cycle rapidly, dividing by binary fission every 6 to 12 hours, and infectious cysts shed in feces can survive in cold freshwater for up to three months.
Zoonosis
/ zoh-ON-oh-sis / · Greek zoion (animal) + nosos (disease)
Zoonosis is an infectious disease that transmits naturally between non-human vertebrate animals and humans, with the animal population serving as the primary reservoir for the pathogen.
Transmission routes include direct contact with infected animals or their tissues, bites from arthropod vectors such as ticks and mosquitoes, consumption of contaminated food or water, and inhalation of infectious aerosols from animal excreta. More than 200 recognized zoonotic diseases exist, and they account for approximately 60 percent of all known human infectious diseases. Reservoir animals often carry the pathogen without showing signs of illness; white-footed mice (Peromyscus leucopus) harbor Borrelia burgdorferi, the bacterium causing Lyme disease, with no apparent harm to the mouse.
Spillover risk rises when humans encroach on wildlife habitat, intensify livestock production, or trade live animals across geographic boundaries. Surveillance programs that monitor pathogen circulation in animal populations, such as global networks tracking avian influenza H5N1 in wild birds, form a central pillar of pandemic preparedness.
Nipah virus, first identified during a 1998 outbreak in Malaysia that killed 105 people, was traced to fruit bats (Pteropus species) roosting in mango trees overhanging pig farms. Pigs amplified the virus before it reached humans, illustrating how a single ecological overlap can launch a deadly zoonotic outbreak.
How To Become An Infectious Disease Specialist? →Reservoir animals always become visibly sick when carrying a zoonotic pathogen. Many reservoir species maintain high pathogen loads with little or no disease, a tolerance that allows the microorganism to persist in the population and remain available for transmission to humans.
White-tailed deer (Odocoileus virginianus) in the eastern United States carry Borrelia burgdorferi without developing Lyme disease symptoms. Black-legged ticks (Ixodes scapularis) feeding on infected deer can acquire the bacterium and transmit it to humans, with nymphal ticks, which are roughly 1 to 2 millimeters in size, responsible for the majority of human cases because they are small enough to go unnoticed during feeding.
Zoonotic Disease
/ zoh-oh-NOT-ik dih-ZEEZ / · From Greek zoon, meaning animal, and nosos, meaning disease.
Zoonotic Disease is an infection caused by a pathogen that originates in non-human animals and spreads to humans through direct contact, vector bites, contaminated food or water, or environmental exposure.
Approximately 60 percent of known human infectious diseases and 75 percent of emerging infectious diseases are zoonotic in origin, reflecting how frequently pathogens cross the animal-human barrier. Major zoonotic diseases include rabies, Lyme disease, avian influenza, Ebola, and COVID-19, which genomic evidence links to bat coronaviruses. Wildlife trade, habitat destruction, and agricultural intensification bring humans into closer contact with animal reservoirs, accelerating spillover events.
Domestic animals contribute substantially to this burden: dogs transmit rabies across much of Asia and Africa, cattle spread brucellosis to farmers and veterinarians, and poultry flocks amplify influenza strains with pandemic potential. One Health frameworks, adopted by the World Health Organization and partner agencies, address zoonotic disease by coordinating human medicine, veterinary science, and environmental monitoring under a single surveillance structure.
Cats infected with Toxoplasma gondii shed oocysts in their feces for only one to three weeks of their lives, yet that brief window produces millions of oocysts per day. Soil and water contamination from this shedding has resulted in an estimated one-third of the global human population carrying latent Toxoplasma infections.
Zoonotic diseases come only from wild animals. Domestic animals including dogs, cats, and livestock transmit numerous zoonoses to humans, among them ringworm, salmonellosis, Q fever, and brucellosis, often through routine daily contact.
Rabies virus circulates in bat, raccoon, and dog populations worldwide and kills approximately 59,000 people each year, with more than 95 percent of deaths occurring in Asia and Africa. Post-exposure prophylaxis, a series of vaccine doses given after a bite, is nearly 100 percent effective when started before symptoms appear, but once clinical signs develop, survival is exceptionally rare.