PARASITOLOGY - science which deals with the study of parasites ( strictly speaking only animal parasites).

PARASITES – come from the Greek word “Parasiton” which literally means eating one another’s table.

Common Parasites of Man

Common Parasites of Man

Common Parasites of Man

When the world is still young, parasitologists postulated that there are no parasites, all organisms started as free living. But since no living organism can live by itself ( No man is an island ) there is the need for organisms to interact with each other. Out of the need for interaction, several types of associations appeared. These are the following:

1. MUTUALISM/ SYMBIOSIS2. COMMENSALISM3. PARASITISM

Mutualism- is an association of 2 distinct type of organisms in which both parties are benefited. Example: A & B associations. A is benefited and B6 is likewise benefited. Plants give off oxygen needed by animals. Animals give off carbon dioxide needed by plants.

Commensalisms- an association between two distinct types of organisms in which one organism (A) benefits from the other (B) B does not get benefit from the A but B is not injured or harmed by A. Association between the shark and the remora fish. The shark give a free ride to the remora fish at the site of their feeding ground. The remora can feed on the feeding ground of shark and is therefore benefited. The shark does not get any benefit.

Parasitism- our subject matter is an association of 2 different types of organisms in which one party (A) gets shelter/ food from the other (B). B does not get benefit from A. In the course of their association B is always injured or harmed by A. This one way type of relationship is considered a worse type of interaction.

1. PARASITE-characterized by being the smaller than the host; dependent completely on the host and obtain benefit from the host.

2. HOST- larger than the parasite; independent of the parasite; gives benefit and shelter to the parasite

In parasitism the associating organisms are:

A.WHETHER THEY LIVE INSIDE OR OUTSIDE THE HOST’S BODY

a.)ECTOPARASITES – parasites which live on the surface of the host’s body or cavities/crevices which opens outside the body.Ex. Fleas, louse, ticks, mites

CATEGORIES OF PARASITES

b.) ENDOPARASITES – parasites which live inside the host’s body or in the

fluids/tissue organ of the host

1. Intestine – Ascaris lumbricoides2. Blood – Plasmodium3. Connective tissues – Trichinella4. Visceral organs – Paragonimus

B. ACCORDING TO THE LENGTH OF TIME THEY SPEND IN THE HOST

a) INTERMITTENT – parasites which visits the host occasionally.Ex. Mosquito – they feed and go

STATIONARY – spend a length of time in the host

1. TEMPORARY – a portion of their life cycle was spent in the host ( Ex. botflies ) – as larva, parasitize the connective tissue of cattle ; as adult, continue as free living adult fly.

2. OBLIGATE – parasite which spent their entire life in the host except for a time that they occur free in the environment to transfer to another susceptible host. Ex. Ascaris

3. FACULTATIVE – parasites which spent their entire existence in the host and when condition in the environment becomes unfavorable they assume a free living existence.

ABNORMAL PARASITES FROM ABNORMAL HOSTS

1. ABERRANT PARASITES – parasites which wander the host’s body aside from it’s usual site ( Ex. Ascaris)

2. INCIDENTAL PARASITES –

parasites of lower form of animals w/c may eventually be transferred to humans due to peculiar habit of humans (Ex. D. caninum – dogs)

HEMATOZOIC PARASITE – parasite living inside the red blood cell. Ex. malarial parasite

1. CYTOZOIC PARASITE – parasite living inside the tissue cells. Ex. Isopora hominis

2. COELOZOIC PARASITE – parasite living in the body cavities. Ex. Wucheraria bancrofti

3. ENTEROZOIC PARASITE – parasite living inside the linen of the intestine. Ex. Ascaris lumbricoides

OTHER TYPES OF PARASITES

HYPERPARASITISM – when a parasite is infected with another parasite.

The big fleas have small fleas on the back to bite them and the small fleas have lesser fleas and so on and so forth.

SUPERPARASITISM – when a host has 2 or more species of parasites inhabiting it’s body.

TYPES OF HOSTS

1. DEFINITIVE HOST – host which harbors the adult or sexual stage of the parasite.

2. INTERMEDIATE HOST – host which harbors the larvae or a sexual stage of the parasite.

a) FIRST INTERMEDIATE HOST

( in helminth ) – harbors the earliest larval stage of the parasite (usually snails)

a) SECOND INTERMEDIATE HOST – harbors the second level of the parasite infective to the final host, a definitive host. It permits the development in its body without developing any symptoms.

3. RESERVOIR HOST – an animal that harbors the same species of a parasites as in man. (Ex. B. coli – pigs/man)

4. PARATENIC /TRANSPORT HOST – a host that carries a stage of the parasite that does not undergo developmental changes in its body.

Criteria for Successful Parasitism1. Successful Portal of Entry - a parasite must have a successful avenue to enter the host. Entrance of parasites to host can be:

a) PASSIVE ENTRY – by ingestion of hosts of food or drink containing the ova/eggs of the parasite.

Ex. Ova of Ascaris lumbricoides contaminated in food or drinks that were swallowed by host.

b) ACTIVE ENTRY – when the infective stage actively penetrates the intact skin of the host in soil or in water.

Ex. Active penetration of the cercaria of Schistosoma japonicum when human bathe in the infected river.

c) INOCULATIVE – when the infective stage is sucked by an arthropod vector such as mosquitoes and transferred to another host in the next blood meal.

Ex. Malaria caused by Plasmodium carried by Anopheles

2. SUCCESSFUL PORTAL OF EXIT – if a parasites can successfully enter the host it must find way also to leave the host.

1. Parasites of the of the alimentary canal leaves the digestive tract by way of anus thru feces. (Ex. Ascaris, Trichiuris)

2. Parasites of the blood depends on the mercy of the arthropod vector to transfer from one host to another. (Ex. Malaria)

3. Parasite of the lungs can be extruded outside by sputum or may be swallowed and exit via the digestive tract. Ex. Paragonimus

Parasites of lower form of animals can exit the host by being eaten (carnivorous attitude of large animals)

3. The parasites should be able to counteract the defensive immunological mechanism elicited by the host. Actions of macrophage cells, phagocytic properties of the whites cells, etc.

4. The parasite must be able to find a specific site inside the host optimum for its growth and reproduction. The ability of the parasite to establish an ecological niche – a place where all the possible needs and requirement can be found is essential for successful reproduction.

1. Doubling of sexual organs (Ex. T. solium)

2. Production of enormous amount of eggs 1,000,000 per day. Ex. D. latum

3. A sexual stages that remain viable for a considerable period of time. Redia and sporocyts of trematodes – if the next host is net ready, it can stay as a paratenic host.

Successful reproduction of the parasite entails :

Specializations include:1. Highly specialized organs of attachment

(hooks suckers boring apparatus)

2. The remarkable specialization of parasites with regards to their reproduction and life history: every structure, every function, every instinct of the parasites is modified for the sole purpose of reproduction. Hence we can say, a fluke does not eat to live but eats to reproduce.

MAJOR TYPES OF LIFE CYCLES UNDERGONE BY PARASITES

1. a) The first type of life cycle may be complex but the parasitic phase is temporary and limited to the outer surface of the host The life of mosquito is good example. Any other organisms also parasitize man and animals only while while feeding or only accidentally.

Mosquitoes-Micropredators

b) Biting flies, kissing bugs belong to this group as do the larval forms of flukes (flatworms) which attempt to penetrate the wrong host.

c) Organisms grouped into this first type of life cycle are more properly called micro predators than parasites.

2. In the second type of life cycle the parasites spends only a part of its time with the host but more than a brief contact. It may be ectoparasitic or endoparasitic. Some ticks for example remain on their host most of the time, but drop off and lay eggs in the soil. Sometimes a different host is used for each stage in the life cycle. The life of the tick Dermacentor andersoni which carries the causative agent of Rocky Mountain

Spotted Fever is an example. Internal parasite may also spend only part of their lives in their hosts. A hookworm egg for example, hatches in the soil and the larvae must develop into an infective stage before it can enter the host. In this case by burrowing through the skin the threadworm Strongyloides stercoralis which

causes Strongyloidiasis in man sometimes has a life cycle similar to that of the hookworm

but due to little understood factors, it lives far several generations in the soil as non-parasitic

worm.

3. A third type of life cycle includes the many parasites which spend all their lives in or on their host except for the period of transmission of the egg, cyst or other stage from one final host to another. The well known roundworm Ascaris lumbricoides is not normally found outside of the egg apart from the body of the host. A certain amount of development occurs within the egg before it becomes infective, but there is no free-living larval stage similar to that of the hookworm. Protozoan parasites likewise are active only while within the host , the cyst being comparable to the egg of higher organisms in that it is an infective stage.

4. A fourth type of life cycle is similar to 3 but it involves biological vectors. The Chinese liver fluke Clonorchis sinensis follows this type of life cycle. The adult worm lives in the human liver ( also in dogs, cats, and other mammals) and produces eggs which leaves the body through the bile duct and intestine and hatches into free-living larvae which enters snails. After several changes in form, the parasite leaves the intermediate host and enters a third

Host, a fish. Man eats the fish and acquire the larval worm which matures in the liver thus completing the cycle.

5. A fifth type of life cycle occurs when the parasites need not leave the host even from one generation to the next. An example is the mango mite Sarcoptes Scabei

Life cycle of Dermacentor andersoniAdults attached to large mammals

(including man)

Dropped to ground Lay eggs

Eggs develops into 6 – Legged larvae (5000)

Larva can feed already

Attached to small mammals (squirrels)

After 4 days of feeding detached from host

Transforms to nympal stage in the ground

Attached to rabbits

Drop again after several days

Develops into adults

Attached to larger mammals like horses,

mules, man

Adults in Lives and bile ducts

Lay eggs

Defecated in water

Enter snail Bulimidae

Inside snail develops into Sporocysts

Develops into rediaDevelops into cercaria

Develops to metacercaria in fish

Man eats fish

Metacercariac Liberated

Transform to adults

LIFE CYCLE OF Clonorchis sinensis

Hatched into miracidia (1st larval stage

Encyst in freshwater fishes(carp family)

Small intestine

Adults Lay eggs 27,000,000/gm of faces

10 – 14 days develop embryo

Eggs swallowed in contaminated foods

and drinks

Eggs hatch in small intestine

Larva penetrates nucleus membrane

Goes to internal organs

Goes to trachea and Lays

esophagus

Life Cycle of A. lumbricoides

Back to small intestine

Eggs defecated in faces

LIFE CYCLE OF Sarcoptes scabiePregnant females make tunnels in epidermis esp. thin and delicate

LayerFemales lay eggs in burrows up to maximum of 50 eggs

Eggs develop into larvae after few days very similar

to adult

Larvae transfer to nympal stage 2 –3 days

inside skin

Goes to internal organs

Becomes adults

Adults lives for 4 weeks

Females impregnated by males

After Laying eggs female dies

Nymphs burrow for themselves

Parasite Host Specificity

• Refers to the peculiar mutual adaptation that restricts a parasite to certain host and vice-versa.

• Why are some hosts heavily burdened with a lot of parasites?

• Why do some parasites restrict only to one or few hosts?

1. Both the host and its environment determine the distribution of the parasite.

2. Widely separated hosts may have the same species of parasites but in general the more diverse the environment , the more kinds of species of parasites exist in given host.

GENERAL RULES AND PRINCIPLES APPLIED IN THE RELATIONSHIP OF THE HOST

AND PARASITE

3.When unrelated hosts live together and eat the same food they may possess some parasites in common.

4.The size and ecological differentiation of the area in which the host live is directly correlated with the diversification and distribution of parasites of that host.

5. In all questions concerning distribution of host and their parasite the food factor of the best is of primary importance.

6. Hosts which migrate for long distances tend to lose at least some of their parasites during the course of migration or some after they arrive at new location.

7 Never say that a species does not occur some place simply because it has not been found there.

8 Adult parasitic worms in contrast to protozoa, do not multiply within the host although they may produce eggs or larvae. Additional adult worms must enter from outside the host.

9. When a host is widely distributed some of its parasites such as the protozoa may accompany the host everywhere it wonders, but when intermediate host are involved the distribution of the parasite may be closely restricted simply because the intermediate host has a narrow geographic