Pathophysiology of Parasitic Infections Flashcards
seeks to explain the functional changes that are occurring within an individual due to a disease or pathologic state. The effects caused by parasitic diseases may be so subtle as to be unrecognizable, or they may be strikingly obvious
Pathophysiology
When the balance between host and parasite is tipped in favor of the parasite , a (?) results
disease
On the other hand, if the balance shifts in favor of the hosts ability to inhibit the parasite, the (?) will be damaged and eliminated
parasite
(?) refers to the ability of an infectious agent to gain entry to the host’s tissues and bring about a physiological or anatomical change, resulting in altered health and leading to disease.
Pathogenicity
The factors that contribute to parasite pathogenicity include:
parasite load, tissue tropism, and pathogenesis
The (?) (also referred to as worm burden among the helminths) refers to the number of parasites in or on the host.
parasite
This determines the likelihood of the parasitic disease.
parasite load
Usually, the greater the number of (?) that enter the host, the greater will be the pathological damage.
parasite infective stages
However, a few parasites that have (?) within the host can also have a considerable effect on the host
reproductive phase
reflects the ability of a given parasite to infect a specific organ or sets of organs
Tissue tropism
After entering the host, the parasite migrates to these parts of the body where conditions are suitable for (?).
temporary or permanent residence
Some pathogens are broadly (?), infecting all or most organs, while others are restricted to a giventissue or even to
certain tissue niches.
tropic
refers to the manner of development of a disease.
Pathogenesis
The pathogenic mechanisms of parasites are many and varied, but for the sake of convenience they can be discussed under the headings of:
a. Spoliative action
b. Traumatic or mechanical damage
c. Lytic necrosis
d. Toxic and allergic phenomena
e. Stimulation of host’s tissue reaction
f. Secondary invasion
(?) with parasites robs the host of essential nutrients and substances.
Infection
Depleting or denying the host of these leads to (?) and in the process causing damage to surrounding tissues.
malnutrition
Malnutrition is more likely to occur in individuals with large burdens of parasites. The effects include
stunted growth, wasting, hunger, or more specific signs of micronutrient deficiency.
Some parasites compete with the host by (?), others by (?), a variety of nutrients from the host.
absorbing
ingesting
The tapeworm (?) can absorb vitamin B12 from the contents of the host’s gut against a concentration gradient.
Diphyllobothrium latum
Since (?) is necessary for erythrocyte production and maturation, its deficiency may result in megaloblastic anemia.
vitamin B12
(?) attach to the intestinal mucosa by means of teeth or cutting plates.
Hookworms
Aside from the bleeding at the site of attachment, hookworms ingest human blood, which results in
iron-deficiency anemia.
In other instances, parasites could contribute to malnutrition by
decreasing host nutrient intake, increasing nutrient excretion, and/ or decreasing nutrient utilization
The tiny protozoan (?) robs its host in a different way.
Giardia lamblia
It is concave on its ventral surface and applies this suction cup to the surface of an intestinal epithelial cell.
Giardia lamblia
When many of these parasites are present, they cover so much intestinal absorptive surface that they interfere with the host’s absorption of nutrients. The unused nutrients then pass uselessly through the intestine and are wasted
Giardia lamblia
A scanning electron micrograph of the surface of the small intestine of a gerbil infested with Giardia sp. protozoa. The (?) is almost entirely obscured by the attached Giardia trophozoites.
intestinal epithelial surface
(?), or destruction of cells, tissues or organs brought about by parasite attachment, feeding, blockage, or migration by is common in parasite infections.
Physical trauma
The attachment of hookworms into the host intestinal mucosa by their teeth or cutting plates results into traumatic destruction of the (?) and bleeding at the site of attachment.
villi
Large numbers of Ascaris lumbricoides worms form tangled mass called (?) that can lead to intestinal obstruction.
bolus
It is also known to migrate and enter the appendix, ciliary and pancreatic ducts, or the common bile duct, perforate the intestinal wall, or may penetrate the parenchyma of the liver and even the lungs.
Ascaris lumbricoides
Another pathogenic mechanism is by interference with the vital processes of the host through
parasitic enzymes.
Enzymes elaborated by many parasites do not only make it possible for them to (?) in the immediate environment and to transform this nutrient into their own protoplasm but also to (?) to promote invasion and spread of parasites.
digest available food
degrade tissues or cells
The dysentery amoeba, (?), trophozoites that secrete cysteine proteinases which do digest cellular materials and the mucosa of the large intestine, forming ulcers and abscessed pockets that can cause severe disease.
Entamoeba histolytica
typical flaskshaped ulcer
intestinal amebiasis
The normal secretions and excretions of parasites and the products liberated from dead parasites accumulate in the host tissues and become toxic to the host, behave like foreign proteins and give rise to various
allergic manifestations
Lysis of the red blood cells parasitized by Plasmodium spp. in malaria unleashes large amounts of waste products and cell debris into the blood, to which the host responds with a sharp rise in (?)
TNF and other pro-inflammatory cytokines
(?) and consequent eruption of TNF accounts for the periodicity of the typical paroxysms of chills and fever in malaria
Synchrony of red cell lysis
Some manifestations of the immune response are responsible for much of the pathogeneses hosts suffer. Parasites provoke tissue reaction that consists of (?) at the site of the parasite and may involve increase in certain types of cells — (?)
cellular proliferation and infiltration
lymphocytes, neutrophils, and macrophages.
When (?) are unable to destroy the parasites, since most are too large to be engulfed, one of the end products of an immune response is the formation of (?).
neutrophils and macrophages
granuloma
This basically consists of a cellular reaction to the presence of parasite which is eventually surrounded by epitheloid cells and multinucleated giant cells and as it dies off, calcium is deposited within the cell.
Granuloma
the physical presence of such structure may block fluid flow and lead to necrosis of the surrounding tissues
granuloma
A few parasitic infection have been shown to lead to (?).
malignancy
The liver fluke, (?), may induce bile duct carcinoma
Clonorchis sinensis
(?) may cause urinary bladder cancer
Schistosoma haematobium
A parasite may open pathways in the skin or gastrointestinal tract for the entry of other pathogens in the tissues
Secondary invasion
In some helminthic infections, the migrating larvae may carry viruses and gram-negative bacteria from the intestines to the blood and tissues, as in
strongyloidiasis, trichinosis, and ascariasis.
pathogenic parasites are endowed with special properties that enable them to cause disease if given the right opportunity. Because of the possibility of recovery after a parasitic disease, there is no doubt that a host has protective mechanisms against the parasites.
Host Defense
two types of host defense:
innate and adaptive
parasites are well adapted to resisting
host innate defenses
are critical in attempts by the host to control such infections.
Adaptive responses
Distinctive host responses to parasitic infections, especially in helminth infections, are (?) - an increase in the number of eosinophils in the blood or tissues, and elevated serum IgE level.
eosinophilia
Their primary function is considered to be defense against organisms that are too large to be phagocytosed, particularly parasitic helminths.
eosinophils
Eosinophils and IgE play a critical role in what is known as (?), a particularly important mechanism against parasites.
antibody-dependent cellular cytotoxicity (ADCC)
bind to the surface antigens of the parasite and eosinophils attach to the Fc portion of the IgE triggering eosinophil degranulation.
IgE antibodies
The toxic products of the (?) can either kill, damage, or dislodge the parasite as a protective host mechanism.
released eosinophil granules
(?) with parasitic infections differ significantly from that in viral and bacterial infections.
Acquired immunity
(?) against parasitic infections is much less efficient and not absolute. It is apparent from the chronic course and recurrences of parasitic infections.
Immunological protection
(?) provide their human host an intense antigenic challenge because they are more antigenically complex than bacteria or viruses
Parasites
Several factors may contribute to this:
• Large size.
• More complex structure.
• Metabolic diversity.
• Complicated life cycle.
• Have evolved to be closely adapted to the host.
This immunity, either complete or partial, may be maintained only while the parasites are present—the phenomenon is known as (?) (or concomitant immunity).
premunition
The parasites remain alive, but its reproduction and other activities are restrained by the (?).
host response
Once the parasitic infection is completely eliminated, the host becomes again (?) to reinfection.
susceptible
Parasites could not survive in their hosts if they could not evade the host defenses mounted by immune responses. As noted earlier, parasites have evolved in relation their host. Consequently, they have developed numerous ways to overcome the host’s defense mechanisms.
Parasite Immune Evasion Mechanism
Many parasites inhabit body sites that are inaccessible to immune response.
Seclusion
Some parasites persist in the (?) of the gastrointestinal tract, oral cavity, or urinary tract.
lumen
Unless the integrity of the intestinal mucosa is breached by injury or inflammation, this barrier protects lumen-dwelling parasites, many of which are surrounded by a protective tegument, or (?), from most of the effective humoral and cellular immune mechanisms of the host allowing survival and the opportunity to reproduce.
cuticle
Some parasites can avoid exposing themselves to immune response by becoming (?).
intracellular
inhabit erythrocytes and are able to avoid the effect of antibodies.
Plasmodium spp.
Those that parasitize (?) possess mechanisms to avoid destruction.
macrophages
proliferate in macrophages in various organs because they are able to inhibit the fusion of lysosomes with the parasitecontaining phagosome.
Amastigotes of Trypanosoma cruzi and Leishmania spp.
One way parasites can avoid forces of immune response is by periodically changing antigens of their surface coat, i.e., to undergo
antigenic variation
It may occur with developmental changes in parasite.
antigenic variation
pass through several discrete developmental stages, each with its own particular antigens.
Plasmodium spp.
Immune responses directed at an early developmental stage may be totally (?) against a later stage of the same parasite.
ineffective
Even more intriguing is the ability of some parasites to vary the antigenic characteristics of a
single developmental stage.
have the capacity to express more than 100 different surface glycoproteins. By the time the host has mounted a response against each new antigen, the parasite antigen has changed again.
Trypanosoma brucei
A number of parasites are able to coat themselves with host molecules. In this way, they are able to hide their own antigenic surface from the immune system
Antigenic disguise
may immunologically hide from the host by masking themselves with host blood group antigens and immunoglobulins.
adult schistosomes
Resemblance between parasite antigen and host antigen is referred to as
molecular mimicry
Some parasites have the (?) to synthesize antigens identical to those of its host.
genetic information
Parasites produce substances that are transported to their (?) that mimic substances naturally found within the host.
tegument
In this case the antigenic determinants of the parasite are so closely related chemically to (?) that the immunological cells cannot distinguish between the two and an immune response cannot be raised.
host “self” components
The larval stage of (?) in the hydatid cyst has been found to carry P blood group antigen, and the tegument of Schistosoma spp. adult can acquire antigenic molecules from the host.
Echinococcus granulosus
Parasites liberate antigenic surface components and, later, regenerating them. The antigens shed are able to combine with and (?) before they reach the target parasite.
neutralize antibodies
Parasites can reduce the immune function by destruction of immunologic mediators. This means that the host shows depressed immune responses to antigens in general, including those of the infecting pathogen.
Immunosuppression
Tapeworm larvae produce
anticomplementary chemicals
(?) splits the Fc component of attached antibodies, rendering it incapable of activating complement.
Trypanosoma cruzi
Several protozoa, most notably (?) that are responsible for African sleeping sickness, induce polyclonal B-cell activation leading to the production of nonspecific immunoglobulins and eventual exhaustion of the antibody-producing capacity of the host.
Trypanosoma brucei species
often cause anemia.
trypanosomiasis and malaria
can result in bowel obstruction
Ascariasis
can cause diarrhea.
amoebiasis
