[DISCUSSION] MODULE 3 UNIT 1 Flashcards
Unicellular
PROTOZOA
Single cell for all functions
PROTOZOA
Kingdom: Protista
PROTOZOA
Majority can replicate inside the infected host
PROTOZOA
Multicellular
HELMINTHS
Specialized cells
HELMINTHS
Kingdom: Animalia
HELMINTHS
Majority does not replicate inside the host
HELMINTHS
Multicellular, bilaterally symmetrical animals having three germ layers
HELMINTHS
- Phylum Platyhelminthes (flatworms):
i. Class: Cestoda (tapeworms)
ii. Class: Trematoda (flukes or digeneans)
- Phylum Nemathelminthes:
i. Subclass: Adenophorea (Aphasmidia)
ii. Subclass: Secernentea (Phasmidia).
(Aphasmidia)
Nemathelminthes, Adenophorea
(Phasmidia).
Nemathelminthes, Secernentea
tapeworms
Platyhelminthes, Cestoda
flukes or digeneans
Platyhelminthes, Cestoda
flatworms
Platyhelminthes
Elongated, cylindrical, unsegmented
Nematohelminthes (Nematode)
Dorsoventrally flated leaf-like or tapelike
Platyhelminthes (cestode, trematode)
Segmented or unsegmented
Platyhelminthes (cestode, trematode)
Separate (diecious)
Nematohelminthes (Nematode)
Mostly hermaphroditic (except schistosomes)
Platyhelminthes (cestode, trematode)
Body cavity Present
Nematohelminthes (Nematode)
Body cavity Absent
Platyhelminthes (cestode, trematode)
Alimentary canal Complete
Nematohelminthes (Nematode)
Alimentary canal Incomplete
(trematodes)
Alimentary canal Absent
(cestodes)
are among the most abundant animals on Earth.
Nematodes
They occur as parasites in animals and plants or as free-living forms in soil, fresh water, marine environments, and even other unusual places.
Nematodes
The number of named species is about (?), but it is probable that only a small proportion of the free-living forms have been identified.
20,000
Greek: nema- meaning
“thread“
Elongated, cylindrical worms with an unsegmented body
NEMATODE
referred to as roundworms because they are round when viewed in cross-section
NEMATODE
Possess a relatively well-developed complete alimentary canal, with an anus
NEMATODE
Body cavity is present
NEMATODE
Head does not have suckers or hooks, but may have a
buccal capsule with teeth or cutting plates
Sexes are separate
(diecious)
The male, which is smaller than the female, commonly has a (?) posterior end.
ventrally curved or coiled
Either oviparous or larviparous
NEMATODE
The most common life cycle pattern among parasitic nematodes is direct. However, some use an indirect cycle with 2 hosts.
(filaria and Dracunculus)
The life cycles of the individual nematodes are similar but
parasite-specific
The specifics of each nematode organism’s life cycle are addressed on an
individual basis.
In their life cycle, nematodes may assume three (3) basic morphologic stages:
egg, larva (pl. larvae), and adult worm.
Nematode eggs differ greatly in
size and shape
Egg
the shell is of variable thickness, usually consisting of three layers which protects the
ovum
Nematode egg shell layers
o an innermost thin, impermeable lipid layer
o a middle, tough and chitinous layer
o an outer vitelline membrane.
Terms generally used in reference to eggs are the following:
- Fertilized (fertile)
- Unfertilized (infertile)
laid by gravid (i.e., pregnant) female worm following copulation (mating) with a male worm
Fertilized (fertile)
under proper incubation conditions, the (?) develops
fertilized ovum (zygote)
a product of unmated female worm, therefore, will not develop further
Unfertilized (infertile)
having smaller cells, called blastomeres, formed by cleavage, a series of consecutive cell division of the fertilized ovum
Segmented
after a number of cleavages, a solid mass of blastomeres, called morula, is formed.
Segmented
the ovum/zygote is in one-cell stage
Unsegmented
having an embryo (developing larva) which is an important criterion for egg maturity
Embryonated
might refer to an egg that is “immature”, i.e., not yet well into the process of development until egg contains a visible embryo; or it may be unfertilized so such egg will not contain a viable zygote
Unembryonated
There are four larval (or juveline) stages of a nematode life:
○ first-stage (L1, rhabditiform larva)
○ second-stage (L2)
○ third-stage (L3, filariform larva)
○ fourth-stage larva (L4)
first-stage
L1, rhabditiform larva
third-stage
L3, filariform larva
The egg embryonates and (?) develops inside the egg.
During each larval stage, a (?) happens where the cuticle is shed, allowing the nematode to increase in size.
After reaching a particular stage of growth and favorable conditions are present, the (?) and the larva emerges from the egg shell.
A molt of the L4 stage results into the (?) (either male or female) which occurs in the definitive host.
(?) reside in their preferred habitat, where they concentrate on obtaining nutrition and reproduction.
Depending on the species, the adult female nematode may lay eggs ((?) female) or larvae ((?) female); some produce eggs containing fully formed larvae ((?) female).
L1
molt
egg hatches
adult stage
Adults
oviparous, viviparous, ovoviviparous
Most often, the infective stage is the (?) with first-stage larva for (?) and the third-stage larva for the (?).
embryonated egg
Adenophorea
Secernentea
In other nematodes, infection is brought by the (?) that have hatched from the egg.
larvae
Infection of humans with different species of nematodes is by:
i. ingestion of the infective stage egg or larva
ii. larval penetration through the skin of the host
iii. transmission of larvae by the bite of an insect
i. ingestion of the infective stage egg or larva
Ascaris lumbricoides
ii. larval penetration through the skin of the host
Necator americanus
iii. transmission of larvae by the bite of an insect
Wuchereria bancrofti
Ascaris lumbricoides
Small intestine
Hookworms-Necator americanus
Small intestine
Ancylostoma duodenale
Small intestine
Strongyloides stercoralis
Small intestine
Capillaria philippinensis
Small intestine
Trichinella spiralis
Small intestine
Trichuris trichiura
Large intestine
Enterobius vermicularis
Large intestine
Capillaria hepatica
Extraintestinal sites
Filaria
Extraintestinal sites
Dracunculus medinensis
Extraintestinal sites
In general terms, the effect of parasitic nematodes on the host depends upon the following factors:
i. the worm burden ii. the habitat of the parasite iii. the activities of the parasite iv. the length of time the infection persists v. the overall health of the host
Since the nematodes can only rarely multiply in humans, the number of parasites present is a critical factor in determining the amount of damage to the host.
Worm Burden
In most cases, an infection of a small number of worms in a relatively healthy individual may remain asymptomatic or cause minimal discomfort.
Worm Burden
However, patients who have a heavy worm burden, particularly if combined with other health problems, are probably more likely to experience severe symptoms and/ or complications.
Worm Burden
The local reaction to adult worms in the intestine are generally minimal. Many infected patients are asymptomatic, but manifestations of infection include abdominal pain, diarrhea, nausea, vomiting, fever. Skin irritation, the formation of skin blisters, and muscle involvement may also be present.
Habitat
The pathogenicity of intestinal nematodes may be due, in part, to migration of adults or larvae through human tissues such as liver or lungs, piercing of the intestinal wall, bloodsucking activities of adult worms, or allergic reactions to substances secreted or excreted by either adult worms or larval stages.
Habitat
This can be serious in heavy infections.
Habitat
Pathogenicity induced by the tissue-dwelling adult nematodes primarily results from immune and nonspecific host responses to the parasite secretions and excretions and to degenerating parasite material. In some cases it may result from circulating larval stages. Migrating nematodes are usually associated with blood or tissue eosinophilia.
Activity
Nematodes are long-lived worms. Infections with nematodes have been known to last for up to 12 months or longer (some infections may last 10 to 15 years or more), depending on the specific species involved. The occurence of reinfections and/or autoinfections may increase the infection time up to several years and beyond; some infections persist indefinitely.
Length of Infection
The occurrence of reinfections and/or autoinfections may increase the infection time up to several years and beyond; some infections persist indefinitely.
Length of Infection
