Mechanical

effect

Effects of Parasites on Hosts

The parasites usually have a negative effect on the host,

causing various diseases.

Disease-causing parasite forms (stages) are termed

pathogenic.

Parasite forms (stages) that do not cause diseases are termed

nonpathogenic.

The parasites can have a number of effects on the hosts,

as listed below:

•Mechanical effects

•Toxic effects

•Allergic reactions

•Feeding off the host

•Side effects

•Environmental effects on humans.

In liver In gall-bladder

Mouth and abdominal suckers

Mechanical effect of (Fasciola hepatica)

Body covered with prickles

Adult flukes

Mechanical effect

• Pork tapeworm Taenia solium fina – Cysticercus cellulosae

Hooks and suckers

on the scolex The length of adult tapeworm may be 10-12 meters

a) In brain b) Removed from brain

Large intestinal

roundworm of

humans

(Ascaris

lumbricoides)

Pinworm Enterobius vermicularis

EggsFemales deposite eggs on the perianal

ridges during the night time

Adult worms

No comment

Trichina

Trichinella

spiralis

Trichina (Trichinella spiralis)

may cause allergic reactions

Symptoms – a classic sign of trichinosis is periorbital edema,

swelling around the eyes. Splinter hemorrhage in the nails is

also a common symptom.

Prevention – investigation of skeletal striated muscles

of infected pork

Cysts with coiled larva inside in raw meat, often pork, wild boar, rat, bear

Plasmodium

malariae

Ring stage Ameboid stage

Mature schizont Released merozoites

Ruptured erythrocite

Mechanical and toxic

effect

Namų dulkių erkių

ekskrementai ir žuvusių erkučių

kūneliai sukelia astmą ir

alergines reakcijas.

Galvinė, drabužinė ir kirkšninė

utėlės sukelia ligą – pedikuliozę

(simptomai – alerginės reakcijos,

stiprus niežėjimas, dermatitas)

Niežinė erkė sukelia odos

ligą – niežus (skabiozę).

Simptomai – alerginės

reakcijos - labai stiprus

niežėjimas, perštėjimas,

šlapiuojančios pūslelės.

Effects of Hosts on Parasites

The hosts respond to the negative effects of the parasites. The

relationship between them is antagonistic (hostile). The host

response aims to subdue or destroy the parasite

Healthy way of lifeThe host response may be divided into

local and general response

•Local response at the cellular level

•Local response at the tissue level

•General response (also humoral or

immune reactions)

•Host response may consist of both

reflexive and conscious activity.

•Reflexive responses are the host’s

defense controlled at the

subconscious level

•Conscious responses may involve

following a healthy way of life

Adaptations can be classified as either progressive or

regressive, or biological.

•Progressive adaptations -

Parasite has developed certain of its parts to a higher level

of functionality.

•Regressive adaptations -

Involve the simplification or disappearance of certain organs

of the parasite.

•Biological adaptationsEnable the parasites to survive better, but cannot be

explained as simply atrophy or development of new organs

for the parasites.

Morphological Adaptations of Parasites

A model for the role of rhomboid-like proteases during red blood cell invasion by the malaria

merozoite. The model is based on work in the related apicomplexan parasite Toxoplasma

gondii. Initial binding (A) is mediated by surface-resident adhesins such as MSP1 (not shown

for clarity). Reorientation and junction formation (B) is through limited release of higher

affinity adhesins (blue) from micronemes. Rapid upregulation of microneme secretion then

occurs; the adhesins interact with a sub-plasmalemmal actinomyosin motor and are

translocated towards the posterior pole of the parasite (C-D), in the process driving forward

motion of the parasite. The adhesins finally come into contact with a rhomboid-like protease

(green) located at the posterior pole, when they are cleaved within their transmembrane

domains and released (E), allowing completion of invasion.