Ascaris, Trichuris, Enterobius, Ancylostoma, Strongyloides and Trichinella Nematoda, and the disease - PowerPoint PPT Presentation

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Ascaris, Trichuris, Enterobius, Ancylostoma, Strongyloides and Trichinella Nematoda, and the disease

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Title: Ascaris, Trichuris, Enterobius, Ancylostoma, Strongyloides and Trichinella Nematoda, and the disease


1
Ascaris, Trichuris, Enterobius, Ancylostoma,
Strongyloides and Trichinella (Nematoda), and the
diseases that these roundworms cause in
humansPaul R. EarlFacultad de Ciencias
BiológicasUniversidad Autónoma de Nuevo LeónSan
Nicolás, NL, México
2
Parasitic nematodes inhabit many thousands of
plant and animal hosts. Some of the most common
parasitic roundworms in humans are a) Ascaris
lumbricoides, the large intestinal roundworm that
causes ascariasis, b) Trichuris trichiura, the
whipworm that causes trichuriasis, c) Enterobius
vermicularis, the pinworm of enterobiasis, d)
Necator americanus and Ancylostoma duodenale, 2
types of hookworms that cause ancylostomiasis, e)
Strongyloides stercoralis responsible for
strongyloidiasis and f) Trichinella
spiralis which causes trichinosis that perhaps
ought to be called trichinellosis.
3
A parasite is an organism that exists by
depending on another organism. Parasites that
infect humans are much more widespread and
prevalent than many people realize. Nematode
diseases are important health problems for rich
and poor throughout the world. As with other
parasitic diseases, some roundworm infections are
more common in warm climates than in cooler,
temperate areas. Many roundworm parasitic
diseases result from human carelessness and lack
of appropriate personal hygiene and sanitation
measures. Thus, the best solution to the problem
rests in preventing these infections rather than
in curing them.
4
Roundworms or nematodes are a group of
invertebrates (animals having no backbone) with
long, round bodies. They range in size from those
visible to the naked eye to those several
hundredths-of-a-mm long and visible only under a
microscope. Most roundworms or their eggs are
found in the soil and can be picked up on the
hands and transferred to the mouth or can enter
through the skin. With the exception of the
roundworm that causes trichinellosis found in
muscles, mature roundworms invade the human
intestines and cause a variety of health
problems.
5
Ascaris lumbricoides. The incidence is over
1500 million infections annually. Of these cases,
about 210 million are symptomatic. In some
rural settings with poor sanitation, perhaps half
the children of 2-12 years have ascariasis.
Then many of them will also have trichuriasis
and various of other chronic illnesses.
6
40cm
7
A mass or bolus of Ascaris lumbricoides.
8
Trichuris trichuriura. These whipworms
cause 800 million infections per year worldwide.
Trichuriasis occurs in the southern United States
and Latin America. Female whipworm,
Trichuris trichiura.
9
Enterobius vermicularis.
Enterobius vermicularis male.
Enterobius vermicularis female.
Enterobius egg in feces.
10
Necatur americanus and Ancyclostoma duodenale.
The human hookworms include 2 nematode
(roundworm) species, Ancylostoma duodenale and
Necator americanus. Adult females measure 10-13
mm for A. duodenale and 9-11 mm for N.
americanus. adult males 8 to 11 mm (A.
duodenale), 7 to 9
mm (N. americanus).
11
Ancyclostoma duodenale.
12
The second most common human helminthic infection
after ascariasis is ancylostomiasis. Worldwide
distribution, mostly in areas with moist, warm
climates. Both N. americanus and A. duodenale are
found in Africa, Asia and the Americas.  Necator
americanus predominates in the Americas and
Australia, while only A. duodenale is found in
the Middle East, North Africa and southern
Europe.
13
Strongyloides stercoralis has both freeliving and
parasitic life cycles. In the parasitic life
cycle, female worms are found in the superficial
tissues of the human small intestine. There are
no parasitic males. The female worms produce
larvas parthenogenically (without fertilization)
and the larvas are passed in the host's feces.
The presence of nematode larvas in a fecal sample
is characteristic of strongylodiasis. Once
passed in the feces, some of the larvas develop
into freeliving larvas, while others develop into
parasitic larvas. The freeliving larvas will
complete their development in the soil and mature
into freeliving males and females.
14
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15
Two types of cycles exist in Strongyloides. 1/
Freeliving cycle The rhabditiform larvas passed
in the stool can either molt twice and become
infective filariform larvae (direct development)
or molt 4 times and become freeliving adult males
and females that mate and produce eggs which
hatch as rhabditiform larvas that can either
develop into a new generation of freeliving
adults, or into infective filariform larvas. The
filariform larvas penetrate the human host skin
to initiate the parasitic cycle.
16
Trichinella spiralis
Muscle can be squeezed between 2 plates of glass
to reveal microscopic larvas.
17
Trichinosis is probably best known as a parasite
that humans contract from eating raw or
undercooked pork. Through an aggressive program
of meat inspection, the incidence of trichinosis
in pigs in the US has been lowered to less than
1, so it is unlikely that those pork products
will contain Trichinella larvas. Most recent
outbreaks of trichinosis in the US have been
traced to pork products from pigs that have not
been inspected and that have been slaughtered
privately. As T. spiralis is not host specific,
hunters should be careful when preparing meat
from their kills, e. g., infections have been
traced to contaminated bear meat.
18
Endnote. We have introduced you to soil
transmitted nematodes and to Trichinella spiralis
transmitted in undercooked meat. The much greater
problem is the sanitation of food, water and
waste disposal. The lack of safe water and
drainage is allied to poverty and high birth
rates. No water delivered to the home and dirt
floors are common aspects of poverty. How many
houses have latrines? The migrant can live
anywhere as long as he can get a job. Shantytown
barrios have sprung up over much of the world and
deteriorate their environments.
19
Parasitic diseases are part of this, although
generally they cannot be vaccine prevented.
Massive population treatments with one-time 400
mg mebendazole or the like may be the road to
take. These populations are infected yet not
seeking treatment. Worms have never been seen
damaging enough to eradicate. Perhaps the
determination needed to eliminate roundworms is
at the end of the rainbow. Generally, people with
parasitoses are poor, and many are rural. Is
industry the real solution? It is the only
solution ! Finally, world economics is such that
the pills like the vaccines MUST be given by
generous donors like Merck.
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