1 introduction to veterinary parasitology

ParasitologyTheory

Education's purpose is to replace an empty mind with an open one. Malcolm Forb

General Veterinary Parasitology

Para 102 2 (1-2)

Books Recommended • Akhtar, M., M. A. Hafeez and C. S. Hayat 2003. General

Parasitology and Protozoology. The Elite Scientific Publications Faisalabad, Pakistan.

• Iqbal, Z., M.S. Sajid, A. Jabbar, Z.A. Rao and M.N. Khan, 2006. Techniques in Parasitology. ISBN 969-417-089-3. Higher Education Commission, Islamabad-Pakistan

• Roberts, L.S. and J.J. Janovy, 2000. Foundations of Parasitology. 5th Edition, W.C.B. Company, U.K.

• Soulsby, E. J. L., 2006. Helminths, Arthropods and Protozoa of Domesticated Animals. The English Language Book Society Bailliere Tindall, London.

Books Recommended• Ash, L.A. and T.C. Orihel, 1991. Parasites: a guide to laboratory

procedures and identification. ASCP Press. American Society of Clinical Pathologists.

• Roberts, L. and J. J. Janovy, 2008. Foundations of Parasitology. 8th Ed. McGraw-Hill Science, USA.

• Hayat, C.S. and M. Akhtar, 1999. Parasitic Diagnosis. UGC. Govt. of Pakistan.

• Iqbal, Z., M. S. Sajid, R. Z. Abbas and M. N. Khan, 2003. Manual of General Parasitology and Protozoology, ISBN 969-8490-07-8. Friends Science Publishers, Faisalabad, Pakistan.

Marks distribution 2 (1-2)Total Marks: 40 Theory: 20

Mid: 6 Final: 12Quiz/Assignments: 2

Practical: 20 Written: 10 Copy+Viva: 5 Class Evaluation: 5 Presentation: 5

Terminology• PARASITISM

Parasite Host

• PARASITOLOGY • 80% of all species of organisms are parasites • Parasitic relationships may be temporary,

facultative, or obligatory

SymbiosisSYMBIOSIS: (="living together") • Definition (German scholar A. de

Bary in 1879)• Any two organisms living in close

association, commonly one living in or on the body of the other

• Symbionts • Different species but not

necessarily

Various types of symbiosis:PHORESIS: ("traveling together" or "to carry")

• PHORONT HOST • Usually one phoront is smaller than the other and is mechanically carried

about by its larger companion • No physiological or biochemical dependence on the part of either

participant. • Examples are bacteria on the legs of a fly or fungal spores on the feet of a

beetle. Dermatobia hominis is a fly whose larva lives beneath the skin of warm blooded animals . The female does not attach her eggs directly to the host of the larva but rather to another insect, such as a mosquito.

• When the mosquito finds an animal upon which to feed, the eggs hatch rapidly, and the larvae drop onto the new host and burrow into its skin.

Gooseneck barnacles (Poecilasma kaempferi) growing on the legs and carapace of a crab

(Neolithodes grimaldi)

• COMMENSALISM: When one member , the COMMENSAL, benefits and the other member is neither helped nor harmedExample: Entamoeba gingivalis in mouth to some degree; some pilotfish and remoras associated with sharks

Mutualism• Mutualism describes a relationship in which both partners benefit from

the association. • Mutualism is usually obligatory, since in most cases physiological

dependence has evolved to such a degree that one mutual cannot survive without the other.

• Termites and their intestinal protozoan fauna are an excellent example of mutualism. Termites cannot digest cellulose because they cannot synthesize and secrete the enzyme cellulase. The myriad flagellates in a termite’s intestine, however, synthesize cellulase and consequently digest wood eaten by their host. The termite uses molecules excreted as a by-product of the flagellates’ metabolism. If we kill the flagellates by exposing termites to high temperature or high oxygen concentration, then the Termites starve to death, even though they continue to eat wood.

PREDATION where one member, the PREDATOR, benefits and a smaller organism, the PREY, is harmed; usually eatenExample: rabbits, cats and mice.

Parasitism• Relationship in which one of the participants, the parasite,

either harms its host or in some sense lives at the expense of the host.

• Parasites may cause mechanical injury, such as boring a hole into the host or digging into its skin or other tissues, stimulate a damaging inflammatory or immune response, or simply rob the host of nutrition.

• Most parasites inflict a combination of these conditions on their hosts.

Basic types of parasitism• ECTOPARASITE (lives on surface of the host).

Appropriate terminology includes the terms "infected" and "infested")

Examples: ticks, lice, fleas• ENDOPARASITE (lives within the host)

Appropriate terminology is "infected;" infested is inappropriate terminology) Example: roundworms in gut; tapeworms in gut• HYPERPARASITE (parasite within a parasite) Examples: malaria in mosquitos; tapeworm larvae in fleas]

Accidental parasiteWhen a parasite enters or attaches to the body of a species of host different from its normal one, it is called an accidental, or incidental, parasite. • Accidental parasites usually do not survive in the wrong host, but

in some cases they can be extremely pathogenic• Accidental parasitism puts both host and parasite into

environmental conditions to which neither is well adapted; it is not surprising that the result may be serious harm to either or both participants.

Example: Nematodes, normally parasitic in insects, to live for a short time in the intestines of birds or for a rodent flea to bite a dog or human.

• Permanent parasite: Some parasites live their entire adult lives within or on their hosts

Example: Mosquito or bed bug, only feeds on the host and then leaves• Temporary, or intermittent parasite: Some parasites living within or on

several different host during entire adult lives on their hosts• Parasitoids: Parasites whose immature stages feed on their host’s body,

usually another insect, but finally kill the host They require a single host Example: insects, typically wasps or flies• Protelean parasites: Parasites whose only immature stages are parasitic

Example: insects belonging to Phylum Nematomorpha (Mermithid nematodes and hairworms

• Anthroponoses: human diseases that can be transmitted to animals

• Epidemic: disease that affects a large number of humans and spreads rapidly

• Epizootic: disease that affects a large number of non-human animals and spreads rapidly

• Epizoic: living on the surface; a skin parasite

• Euryxenous: broad host range• Heteroxenous: alternation of generations of a parasite• Incidence: the number of cases of an infection occurring

during a given period of time in relation to the population unit in which they occur

• Infection: parasitic invasion resulting in injury and reaction to injury

• Latent: non-visible infection

• Monoxenous: single host life cycle

• Parasitemia: parasites in blood

• Pathogenic: results in disease or morbid symptoms

• Premunition: resistance to superinfection; depends upon survival of parasites in host and disappears with their elimination

• Prevalence: number of organisms in a population infected with a parasite at any one time

• Virulence: relative infectiousness of a parasite• Zoonosis: animal diseases that may be transmitted from

animals to humans

Parasite transmission route • INGESTION from food or water / • Inhalation • DIRECT PENETRATION of skin from environment• VECTORS

(transmits parasites from host to host)• BIOLOGICAL VECTOR (essential in life-cycle of parasite)

• MECHANICAL VECTOR (unessential in life-cycle of parasite - phoretic)

Host • DEFINITIVE OR FINAL HOST (host in which parasite reaches

sexual maturity and reproduces)• INTERMEDIATE HOST (some development in host, but does

not reach sexual maturity; often asexual stages)• PARATENIC OR TRANSPORT HOST (no parasite development;

but parasite continues to live and is infective to next host; for instance, pseudophyllidean tapeworm larvae in fish)

• RESERVOIR HOST (non-human animals that serve as sources of infection to humans)

Examples are rats and wild carnivores with Trichinella spiralis, dogs with Leishmania spp.

Host specificity• Some parasites are specific to host infecting only

a single host species • Some infecting a number of related species• Some infecting many host speciesExample: The pork tapeworm, Taenia solium, apparently can mature only in humans, so adult T. solium have absolute host specificity. The nematodes Trichinella spp. Seem to be able to mature in almost any mammal.

Typical characterisitics of parasitism• High reproductive potential: Example: multiple fission in Apicomplexa; hermaphrodism of trematodes; partenogenesis in Strongyloides spp• Often unique morphological or physiological specializations, loss of structures,

etc.Example: loss of digestive tract of tapeworms, loss of wings of fleas and lice and loss of many sensory structures of nematodes• Development and refinement of a TEGUMENT; a living external layer of digenes,

cestodes and acanthocephala that allows digestion and other functions across body surface

• Development of special holdfast organsExample: hooks, suckers, teeth, clamps, cutting plates, spines

• Production of anti-coagulants in leeches and hookworms

• Often special site specificity

• Usually, but not always, non-lethal to host

• Generally more numerous than hosts

• Generally much smaller than host (if larger, then termed a predator)

• Often have evolved methods of evading host immune system

Impact of parasites on domestic animals

• domesticated animals are usually confined to pastures or pens year after year, often in great numbers, so that parasite eggs, larvae, and cysts become extremely dense in the soil, and the burden of adult parasites within each host becomes devastating.

Example,• the protozoa known as coccidia thrive under crowded conditions; they

may cause up to 100% mortality in poultry flocks, 28% reduction in wool in sheep, and 15% reduction in weight of lambs.

• Infections in poultry are controlled by the costly method of prophylactic drug administration in feed. Unfortunately, coccidia have become resistant to one drug after another

Impact of parasites on wild animals

• Less can be done to control parasites of wild animals.• Most wild animals can tolerate their parasite burdens fairly well, but

they will suffer when crowded and suffering from malnutrition, just as will domestic animals and humans.

Example: lungworms have so increased in numbers that in some herds no lambs survive the first year of life. These herds seem destined for quick extinction unless a means for control of their parasites can be found in the near future.

Parasitic zoonosis• Transmission to humans of parasites normally found in wild

and domestic animals. • Many zoonoses are rare and cause little harm, but some are

more common and important to public health. Example: • Echinococcosis, or hydatid disease, in which humans

accidentally become infected with juvenile tapeworms when they ingest eggs from dog feces

• Toxoplasma gondii, which is normally a parasite of felines and rodents, is now known to cause many human birth defects