Microbiology: Parasitology

Cestodes (Tapeworms)

• The three main parts of the cestode body are the scolex, neck, and strobila
• The head of a cestode is called the scolex
• Two types of attachment organs on a cestode's head are suckers and bothria
• Cestodes are hermaphroditic
• Cestodes do not have an alimentary canal
• Cestodes have an indirect life cycle
• A Cyclophyllidea cestode has one intermediate host in its life cycle
• The egg of a Cyclophyllidea cestode contains an oncosphere
• A Pseudophyllidea cestode has two intermediate hosts in its life cycle
• Attachment organs of a Pseudophyllidea cestode are called bothria
• Body segments of cestodes are called proglottids
• The mature segment of the cestode body is located posterior and is called proglottid.
• Reproductive organs in the cestode proglottid include both male and female organs
• Vitelline glands function to produce yolk
• Hooks on the cestode scolex are called rostellar hooks
• The rostellum is a structure that can be present or absent on the scolex
• The variations of the rostellum are called armed and unarmed
• Four different types of larval stages of cestodes are cysticercus, hydatid cyst, coenurus, and strobilocercus
• The larval stage's purpose is dispersal
• The final host of Taenia solium is humans
• The intermediate host of Taenia solium is pigs
• Clinical signs of Taenia solium in the final host include an itchy rear end
• The larval stage of Taenia solium found in the intermediate host is cysticercus
• The result of a human consuming Taenia solium eggs in feces is cysticercosis

Nematodes (Roundworms)

• Nematodes have the following key characteristics: elongate/cylindrical shape, an alimentary canal, sexes usually separate, and are egg-laying
• The five larval stages of nematodes are L1-L5
• Nematodes do not multiply within the host
• Nematode life cycles are direct and indirect
• A general nematode life cycle is Egg -> L1 -> L2 -> L3 -> L4 -> L5 -> Adult
• The infective larval stage of nematodes is L3
• Nematodes ensure survival through survival of eggs with larva, paratenic hosts, transmammary, and transplacental
• Hypobiosis is arrested development
• Identification of nematodes is aided by observing male bursa, vulva, mouth (shape, teeth), esophagus, and size
• Primary clinical signs of Ancylostoma caninum include anemia and lassitude
• Primary modes of infection of Ancylostoma caninum include percutaneous or penetration of oral mucosa, per os, paratenic hosts, transplacental, and transmammary
• Hosts of Ancylostoma caninum are dogs
• Adult Ancylostoma caninum reside in the small intestine
• Adult Ancylostoma caninum eat blood
• The life cycle of Ancylostoma caninum: Adults in the intestine lay eggs -> eggs hatch -> larvae penetrate skin or ingested -> adults develop in the intestine
• Clinical signs of an acute Ancylostoma caninum infection include anemia and lassitude, respiratory disease, and diarrhea (blood and mucus)
• Clinical signs of a chronic Ancylostoma caninum infection include weight loss and poor hair coat
• Hookworms are zoonotic, and the disease is called cutaneous larval migrans

General Parasitology

• A facultative parasite may become parasitic but does not require a host, for example, fungi
• An opportunistic infection is an infection that takes advantage of a weakened immune system
• Parasitism is defined as an organism deriving food from a living organism of another species
• Fleas and copepods are examples of ectoparasites
• Cestodes and trematodes are examples of endoparasites
• Commensalism is a relationship where one organism benefits and the other is unaffected; flagellates feeding on bacteria on the surface of fish
• Mutualism is a relationship where both organisms benefit
• Virulence is the degree of pathology caused by the organism
• Pathogenicity is the ability of an organism to cause disease
• A direct life cycle involves only one host; monoxenous
• An indirect life cycle involves more than one host; heteroxenous
• A paratenic host is a non-required host in which no development occurs
• An aberrant host is a host in which the parasite cannot complete its development; dead-end host

Other Taxa

• Three classes in the phylum Platyhelminthes are Cestoda, Trematoda, and Monogenea
• Monogenea are ectoparasites
• Monogenea are typically found on the skin, fins, and gills of fish
• Monogenea have a direct life cycle involving one host
• Two examples of Monogenea: Gyrodactylus, Benedenia seriolae
• The common name for Acanthocephala is thorny-headed worms
• Adult Acanthocephala are found in the intestine
• Acanthocephala has an indirect life cycle involving two or more hosts
• Termites are the intermediate host of Oncicola venezuelensis; ocelots are the definitive host
• The larval stage of Oncicola venezuelensis found in the mongoose and monkey is cystacanth
• The phylum Myxozoa is related to the phylum Cnidaria
• Fish and annelids are the 2 hosts in the Myxozoa life cycle
• A clinical sign of Myxobolus cerebralis is cartilage destruction and erratic tail chasing behavior ("whirling disease")
• The optimum temperature for the development of major trichostrongylid species is 20 degrees C

Protozoa

• Protozoa are unicellular, eukaryotic, may have a "pseudo-mouth", and may form cysts
• Protozoa move with flagella, cilia, and pseudopodia
• Schizogony is asexual reproduction with multiple divisions of the nucleus and cell
• Eimeria, Neospora, and Balantidium are examples of protozoa
• Important flagellated protozoa are Giardia, Histomonas, and Trypanosoma
• Giardia is transmitted through contamination of water, food, or hands/fomites with infective cysts
• Histomoniasis affects poultry
• Histomonas is transmitted fecal-orally
• Balantidium is an example of a ciliate protozoan
• Eimeria and Toxoplasma are Apicomplexa protozoa
• An oocyst is a cyst containing a zygote