James R. Flowers, PhD(Office hours by appointment)

http://parasitology.cvm.ncsu.edu/

VMP 920Infection & Immunity II

Veterinary Parasitology Section

Studies in Infectious Diseases

Microbiology Virology Bacteriology Mycology

Parasitology Medical & Veterinary Protozoology Helminthology Medical & Veterinary Entomology

Immunology

ParasitologyStudy of Parasitism

Parasitism

Intimate relationship between two heterospecific organisms, in which the parasite, usually the smaller symbiont, is metabolically dependent on the host.

One symbiont (host) is harmed, while the other symbiont (parasite) benefits.

Parasitism

Host Specificity The degree to which a parasite

species infects a single host species

High v/s Low

Dirofilaria immitisEndoparasite with relatively high host specificity for canids

Endoparasite (permanent)

Ectoparasite (intermittent)

High Host specificity Low Host specificity

Dirofilaria immitis

Culex spp.Ectoparasite with Low Host Specificity

Culex spp.

Endoparasite (permanent)

Ectoparasite (intermittent)

High Host specificity Low Host specificity

Type of Hosts Definitive Host --- Host in which parasite reaches sexual

maturity

Intermediate Host (vector) --- Host in which the parasite is metabolically dependent to complete its life cycle

Accidental Host --- A host that the parasite does not normally infect, may or may not complete development. (Maybe a dead-end host)

Paratenic host --- A “transport” host, but the parasite does not require it to complete its life cycle.

Reservoir Host --- An animal host that maintains a parasite population and has the potential to transmit to a human or domestic animal.

Type of Life Cycles

Direct Life Cycle --- Parasite does Not require an intermediate host to complete its life cycle.

Indirect Life Cycle --- Parasite requires an intermediate host to complete its life cycle.

Parascaris equorumHorse – Definitive Host

Direct Life Cycle

Definitive Host Intermediate

Host Accidental Host Paratenic Host Reservoir Host

Direct Life Cycle Indirect Life

Cycle

Canids – Definitive Host(wolf / fox) - Reservior hostsSnail – 1st Intermediate hostFish – 2nd Intermediate hostIndirect Life Cycle

Definitive Host Intermediate

Host Accidental Host Paratenic Host Reservoir Host

Direct Life Cycle Indirect Life

Cycle

• Infection = presence of an agent that has the ability to cause disease

• Disease = the occurrence of dysfunction

• Infectious = capable of causing infection

• Infection ≠ Infectious ≠ Disease

Important Parasitological Concepts

A. The dog showed no adverse symptoms to the 2 female

Dirofilaria immitis in its right ventricle.

Infection, Disease, Infectious ?

Infectio

n B. 1,000 juvenile Haemonchus contortus were causing

severe anemia in the lamb.Infection +

Disease C. Cats suffering from large bowel diarrhea due to

Tritrichomonas foetus pass active trophs in their stool. Infection + Disease +

Infectious

Infection

D. After using the bathroom, she was horrified to see that she had passed several active proglottids of the beef tapeworm, Taenia saginata.

Important concepts to associate with parasitic life cycles, infections, pathogenesis, and dz control. Macroparasites

Large parasites (Adult Tapeworms, Adult Trematodes, most Nematodes, Acanthocephalans, Arthropods)

Individual organisms do NOT Multiply in or on the host.

Dose-dependent

Microparasites Small parasites (Protozoa, [bacteria, viruses]) Individual organisms do Multiply in the host. Generally not dose-dependent

General Groups of Parasites

Dose Dependent

Giardia sp. & other extracellular protozoa

Replication(binary fission)