Veterinary Science
S Mimeographed Report, 59-1 December, 1958


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATI O HUME LIBRARY
JOSEPH R. BECKENBACH, Director
GAINESVILLE, FLORIDA
AUG 4 1972
PARASITES OF ANIMALS INFECTIOUS TO MAN

by I.F.A.S. Univ. of Florida
Leonard E. Swanson, Parasitologis
Department of Veterinary Science

I. General Introduction:

A. Parasitology is the science that deals with parasitism.

1. A parasite is an animal that lives upon or within another

living organism at whose expense it obtains nourishment and

protection without giving anything in return for this relation-

ship.

2. Parasitism is the relationship between the host and parasite.

3. Helminth is a defined term for worms.

4. Helminthology is the study of worms.

B. All animals are parasitized with one form or another of these

helminths.

C. Wild animals are especially heavily parasitized and quite often

serve as reservoirs of infection for domestic animals and man.

D. Domestic animals are a constant source of possible infection of
parasites to man.

II. Relationship of Parasites:

A. Symbiosis The living together of two dissimilar organisms to the
advantage or disadvantage of one or both.

1. Mutualism is a form of symbiosis in which both symbionts are

in more or less measure, benefited by the association.








Example: Protozoan fauna of the intestinal tract of termites

change wood materials to digestible forms.

2. Commensalism is a form of symbiosis in which one symbiont is

benefited, but its co-symbiont is neither benefited nor harmed.

Example: Common colon amebia of man which feed on waste products.

3. Helotism is a form of symbiosis in which one organism enslaves

the other.

Example: Dermatobia hominis, South American skin maggot. The

adult female fly captures other insects, deposits her ova on

their bodies and they in turn serve as a means of transportation.

The maggot larvae are liberated from the eggs 4hile the insect

carrier is obtaining its blood meal from ian or beast.

4. Parasitism is a form of symbiosis whereby the parasite derives

its food and protection, usually at the expense of the host animal,

yet in light infections this association may be of no harm to

either organism. Biologically it is not the intention of parasite'

to overparasitize the host to a point whereby impaired health or

death of the host will result in destruction of the parasite

itself.

B. In summary, a symbiont receiving the benefit is the parasite and the

one receiving the damage is the host.

C. Hosts

1. Final or definite hosts harbor adults or sexually mature parasites.

2. Intermediate hosts harbor larval forms, where an intermediate

host is required to complete the life cycle.

III. Zooparasites are parasites which belong to the animal kingdom:

A. Ectoparasites are those that are parasitic to the surface of the

body or have direct contact to the skin.


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Example: Lice, fleas, ticks, mites, fly larvae, etc.

B. Endoparasites are parasite; which enter the body of the host,

inhabiting the alimentary canal, liver, lungs, blood and other

tissue.

Example: Ascarids, hooks, flukes, amebia, etc.

IV. The influence of parasites upon the host depends upon the number and

age of parasites present, location, the nature of their food, route

through the body of larval forms, environmental conditions, and age

of the host. The effects of parasites on the host also depend on the

balance of minerals, vitamins, proper food intake and general condition

of the host.

V. Parasites Injure the Host:

A. Through mechanical injury such as biting, migration and loss of blood.

Example: 1. Biting-lice.

2. Migrating-ascarid or fluke larvae causing tissue

destruction.

3. Bloodsucking-hookworm.

B. Through obstruction as in the case of a mass infection of ascarids

blocking the intestinal tract and/or bile ducts.

C. By injection of toxins such as occur in extreme hookworm infections.

D. Tissue feeding of maggots.

E. Anaphylactic reaction extreme sensitivity to touch of ascarids.

VI. Internal parasites of man and animal fall into the following phyla

and classes:

A. Phylum Platyhelminthes

1. Class Trematoda

Examples: Liver fluke


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a. Fasciola hepatica and F. gigantica.

b. Clonorchis sinensis.

Blood fluke

a. Schistosoma japonicum.

Intestinal fluke

a. Fasciolopsis buski.

2. Class Cestoda

Example: tapeworms

a. Taenia saginata

b. Taenia solium

c. Echinoooccus granulosus

d. Diphyllobothrium latum

B. Phylum Nemathelminthes

1. Class Nematoda

Example: roundworms

a. Necator americanus

b. Ancylostoma braziliense

c. Enterobius vermicularis

C. Phylum Protozoa

1. Class Infusoria

Example: a. Balantidium coli

2. Class Sarcodina

Example a. Endamoeba coli

b. E. histolytica

3. Class Sporozoa

Example: a. Isospora hominia

b. Plasmodium falciparum


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4. Class Miastigophora

E'-ample: a. Trichomonas vaginalis

VII. Internal parasites of man listed according to their location in the

body are:

A. Bronchial tubes of the lungs

1. Lung fluke

a. Paragonimus westermanii

B. Liver

1. Liver flukes

a, Fasciola hepatica

b. F. gigantic

2. Tapeworms

a. Echinococcus granulosus

C. Small Intestine

1, Threadworms (microscopic in size)

a. Strongyloides stercoralis

2. Hookworms

a. Necator americanus

3. Roundworms

a. Ascaris lumbricoides

4. Tapeworms

a. Taenia saginata

b. Taenia solium

o. Dipylidium caninum (occasional)

d. Diphyllobothrium latum

D. Large Intestine

1. Protozoa








a. Balantidium coli

b. Endamoeba coli

c. Endamoeba histolytica


E. Skin

1. Filaria Wuchereria bancrofti (elephantiasis)

2. Larval migration

a. Ancylostoma braziliense

b. Ancylostoma caninum

F. Muscle

1. Larval migration

a. Trichinella spiralis

VIII. Live Cycles:

A. All parasites of the class Nematoda are what is termed direct infec-

tors. No intermediate host is required, with the exception of

trichinella, which require an intermediate host, the pig, bear, dog,

etc.

1. Direct infectors depend on optimum moisture, temperature and


vegetative conditions to complete their life cycle. The eggs are

passed out of the host animal in the feces and hatch, liberating

a minute larva. This larva, after three or more molts, is known

as the infective stage, which is ingested or enters the body by

skin penetration. Upon reaching the digestive tract the larva

finds its suitable location in the host where it reaches sexual

maturity, mates and begins laying eggs.

2. Filaria depend upon mosquitoes or other biting insects to com-

plete their life cycle. The female worms deposit their larvae

in the host bloodstream and/or tissues. The insect vector,


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feeding on the infected animal ingest the microscopic larvae,

which further develop in the insect and at a subsequent feeding

these larvae are injected into another host animal.

B. Parasites belonging to the class Trematoda require an intermediate

host:

1. Liver flukes, and others of the Trematoda class require a fresh

water snail to complete their life cycle.

a. Fasciola hepatica and Fasciola gigantica

1) The young flukes that hatch from the eggs burrow into

the soft tissue of a fresh water snail where they develop

and multiply. After a period of time they are liberated

into water as young free swimming flukes. These young

flukes swim around in water, attach themselves to vege-

tation and are subsequently eaten by man. This stage in

the life cycle is known as the infective stage to man or

beast.

b. Clonorchis sinensis

1) This fluke life cycle is identical with the exception

that it requires two intermediate hosts, a fresh water

snail as the primary intermediate host and a fresh water

fish as the secondary intermediate host. Man may become

infected by eating improperly prepared fish.

2. Blood flukes.

a. Schistosoma japonicum

1) Blood fluke life cycles are identical to the above ex-

cept that there is a skin penetration by the cercariae

stage instead of encystment on vegetation and no secon-

dary intermediate host is required.


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3. Intestinal flukes

a. Fasciolopsis buski

1) The intestinal fluke life cycle is identical with other

flukes except that the infective stage encyst on water

chestnuts and other plants eaten raw by tropical man

and no secondary intermediate host is required.

C. Parasites belonging to the class Cestoda require an intermediate

host.

1. Taenia saginata; Taenia Solium and Echinococcus granulosus.

a. The human tape worm (Taenia saginata) adults are found in

the human intestinal tract. The gravid segments are passed

to the exterior, ingested by cattle and the embryo penetrates

the intestinal wall, is picked up by the vascular system and

carried to the muscles. They usually locate in the heart

and cheek muscles. In heavy infections they may be found in

any muscle of the body. If man eats raw or partially cooked

meats, he may become infected. In modern plants inspecting

veterinarians examine each and every animal for these cysts

and are able to reduce the incidence of human tapeworm

infections.

b. The human tapeworm (Taenia solium) life cycle is identical

with the above except that swine are the intermediate hosts.

It is also possible for man to serve as both the final and

the intermediate host.

c. The dog tapeworm (Echinococcus granulosus) adult lives in

c the intestines of dogs and wild carnivera. The tapeworm

segments are passed from the host with fecal materials which


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may contaminate human food and/or water supplies. The

infective embryo penetrates the intestinal wall, is picked

up by the vascular system and carried to various parts of

the body, especially the liver where it develops into an

infective hydatid cyst. Sheep, goats and wild ruminating

animals also may eat the contaminated food and become in-

fected as is man. Wild or domestic canine animals may

eat these parasitized intermediate hosts and become in-

fected with the adult tapeworms.

D. Protozoa

1. These parasites may be direct or indirect infectors depending

upon the parasite in question. In the direct infector group

man becomes infected by consuming contaminated food, water and

direct contact with the organism. House flies, birds, rats, man,

etc. may serve as mechanical means of transporting these infec-

tions. The indirect group depend upon insect vectors to complete

their cycle.

a. Those belonging to the malaria group require a mosquito to

complete their life cycle, whereas coccidia which belong to

the same class are direct infectors.

b. Those belonging to the trichomonas, ameba and balantidium

groups are direct infectors.

IX, damage done to the host:

A. parasites, depending upon their location in the host and type of

food required for their existence, injure the animal by feeding on

blood, bacteria, tissue, bile, epithelium, lymph, or by mechanical

blocking of the essential physiological functions of the respective

organs or tissues of the body.


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X. Diagnosis:

Internal parasite infection, whether it be in man or other animal,

cannot be seen in its protected home. The infection may be likened to a

closed book; you do not know of its presence or absence unless accurate

methods of diagnosis are utilized.

Infection may be suggested if man exhibits symptoms of anemia, enlarged

abdomen, irritability and general unthriftyness. The most accurate diagnosis

universally used for determination of parasitism in man is the microscopic

examination of specimens of feces and/or blood for parasite ova and/or larval

forms of parasites.

XI. Prevention

In general parasites must live congenially with their host in order to

produce their kind; however, if by accident, overcrowding, improper diet, un-

sanitary premises, man may become excessively parasitized.

The most critical point to be emphasized in the control of parasitism

in humans is farm, home and personal sanitation. If modern toilet facilities

are not available, outside toilets should be constructed so as to exclude fly

contamination or possible animal invasion. Locate the toilet where possible

contamination of food or water supply for man or animal cannot occur and this

includes protection from heavy storm damage. It is realized that average in-

dividuals will not normally use barns, fields and woods for human evacuation

but it does occur and should be discouraged. Fresh vegetables and fruit eaten

raw should be thoroughly washed, especially those from farmers who may be

prone to use night soil as a fertilizer.

The practice of allowing children to work and play barefoot in tropic

and subtropic areas should be discouraged as this invites heavy hookworm

infections. On beaches and public gathering places where dogs roam, there is


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always the possibility of picking up creeping eruption or hookworm infection

and this can only be guarded against, according to our present knowledge, by

wearing protective clothing. Avoid as much as possible these contaminated

areas. Dogs that are kept as pets around homes should be watched closely and

treated by a veterinarian for the removal of hookworm infection. Also, on

your own premises, it is good common sense to pick up all bowel passages from

dogs and bury or burn same daily. The above not only lessens the possibility

of creeping eruption, but prevents dogs and man from hookworm infection.

The above statements apply equally well to infections with Strongyloidas

sterooralis. Trichinella or tapeworms of humans are only contracted by consamp-

tion of raw or partially cooked meats, especially meats from uninspected source

Pork products even from inspected establishments should not be eaten unless

cooked thoroughly. The meat should have a greyish appearance and not pink or

red when cocked. Beef from inspected establishments may be eaten raw or par-

tially cooked with relative safety as the cysts can be located at time of

slaughter. If found, proper steps to eliminate the parasite in the carcass

are taken before it is offered for human consumption. Fish products should only

be eaten after proper preparation and thorough cooking.

As this outline is prepared for public health sanitarians, it is felt

that they can render the greatest service to communities by advising their

people on methods of prevention, and in assisting Physicians and Veterinarians

in the curtailment and elimination of parasites. Swimming pools, ponds, lakes

or streams should not be used for bathing or drinking purposes until proper san-

itary measures and examinations are taken to reduce possible human infections.


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References:

1. Belding, David L. 1942. Textbook of Clinical Parasitology.
Appleton-Century-Crofts, Inc. New York, N. Y. 888 pp.

2. Morgan, Banner B. and P. A. Hawkins. 1951. Veterinary Helminthology.
Burgess Publishing Company. Minneapolis, Minnesota. 400 pp.

3. Underhill, B. M. 1924. Parasites and Parasitosis of the Domestic
Animals. The Macmillan Company, New York, N. Y. 379 pp.
LES: jm
200 copies