Transcript Document

Enterobius vermicularis
Department of Medical Parasitology
Introduction
• Enterobius vermicularis, commonly known as
pinworm or seatworm
• E. vermicularis is parasitic only to humans
• Adults inhabit the ileocecus, that is, cecum
and adjacent ascending colon and distal ileum.
The infection of E. vermicularis may cause
Enterobiasis
• World-wide distribution, it is commonly found
in kindergarten and primary school students
Classification
Phylum Nemathelminthes
Class Nematoda
Order Oxyurata
Family Oxyuridae
Morphology -- Adult
• Female -- fusiform body
with a long, thin, tapering
tail, 8 to 13mm
• Male -- “6” shape, curved
tail, 2 to 5mm. Males die
right after mating, thus
are rarely seen
• White in color
• Cephalic alae
The anterior end tapers
and is flanked on each side
by cuticular extensions of
head
• Pharyngeal bulb
The esophagus is slender,
terminating in a prominent
posterior bulb
Morphology -- Egg
• Oval in shape, 50~60×25μm in average, a
larva inside
• Clear, colorless and doubly refractive egg
shell, flattened on one side
Life cycle
Adults
Newly laid
eggs
molt
6h
Infective
eggs
molt 3 times
Larvae
Adults
Characteristics of life cycle
• Humans are the only host in nature
• No intermediate host (direct life cycle)
• No larval migration between organs
Infection
Stage Infective eggs
Type • Self-infection:
anus-hands-mouth route
• Cross-infection:
contact transmission
• Inhalation
• Retroinfection
Residence
Stage
Site
Adults
Cecum and adjacent large
and small intestines
Mode
Adhering to intestinal mucosa
Feed
Blood, tissue fluid, epithelial cells
Residence
Habitus
Gravid female crawl out of
anus at night and deposit eggs
on the perianal and perineal
region (anal sphincter relaxed)
Fecundity 15000 eggs/♀
Life span Female 1~2 months
Discharge
Stage Eggs
Mode
Female release eggs
on the perianal zone
Pathogenesis
• Enterobiasis is usually asymptomatic, the adults may
cause slight irritation of the intestinal mucosa
• The most typical symptom is perianal
pruritus (itching and irritation), which
associates with the nocturnal migration
of the gravid females from the anus and
deposition of eggs in the perianal folds
of the skin, may lead to excoriations
and bacterial superinfection
Pathogenesis
• Heavy infection in children may result in
restlessness, sleeplessness, anorexia, weigh loss,
grinding of teeth, nervousness, irritability,
abdominal pain and vomiting
• Sometimes, pinworm may migrate up the female
reproductive tract, cause vaginitis, endometritis
and granuloma in uterus and fallopian tubes.
Occasionally, invasion of the female to the
appendix, the peritoneal cavity or the urinary
bladder may occur
Laboratory Diagnosis
• Microscopic identification of eggs collected in
the perianal area by cellophane (Graham Scotch)
tape method or anal swabs. This must be done
in the morning, before defecation and washing
• Detection of
adult on anal
skin
Epidemiology
Geographical distribution
•
Geographical distribution—cosmopolitan in
temperate zones with about 30~50% of the
population infected, and more prevalent in
children than adults. it is estimated that 500
million people are infected Worldwide
•
Enterobiasis is most common where people
live under crowded conditions such as
orphanages, kindergartens, and large families
Distribution of pinworm in children under the age of 12
(23.6% in average, 71% in Fujian and Jiangsu )
Source of infection
Patients and carriers
Prevalent features
• Multiple ways of infection
• Reinfection
Treatment and prevention
• Albendazole/Mebendazole: 95% effective
• Repeated retreatment may be necessary
for a radical cure
• Personal hygiene and eating habits
• Sanitary disposal of clothing, bed linen,
and environment
• Health education
Trichinella spiralis
Introduction
• Trichinella spiralis is capable of infecting all
mammals, cause parasitic zoonosis--trichinellosis
• Human beings acquire the food-borne trichinellosis
by ingesting the raw or undercooked meat of pigs
and other animals containing the Trichinella larvae
• Larvae which inhabit the striated skeletal muscles
are the main pathogenic stage
• World-wide distribution
Classification
Phylum Nemathelminthes
Class Nematoda
Order Trichurata
Family Trichinellidae
Morphology -- Adult
• Thread like
• Male--1.5mm in length,
female--3~4mm in length
• Ivory-white in color
Morphology -- Larva
• The newborn larvae--100µm long, the fully
developed, encapsulated larvae--1 mm long
• Larvae encyst in skeletal muscle cells
Life cycle
Encapsulated
larvae
Digestive
enzymes
♂die right
after mating
♀
3~5 days
Larvae
Penetrate
mucosa
Molt 4
times，48h
♀,♂mate
Newborn
larvae
Blood
stream
skeletal
muscle
Adults
Encapsulated
larvae
Infection
Stage Encapsulated larvae
Mode Oral infection
Residence
Stage Adults, larvae
Site
Adults--duodenal and jejunal mucosa
Larvae--skeletal muscles of the
tongue, the deltoid, pectoral, and
intercostal muscles, the diaphragm,
and the gastrocnemius
Life
span
Female adults--1~2 months
Larvae--several to 30 years
Characteristics of life cycle
• Adults and larvae live in the same host
(not only final host but also intermediate
host), alternation of hosts is needed to
complete the whole life cycle
• Ovoviviparity
• No discharge or free-living stages
• The only intracellular parasitic nematode
Pathogenesis
Stage Adults, encapsulated larvae (main)
Symptomatology
• Intestinal phase
• Muscular phase
• Convalescent phase
Clinical feature
Fever, myalgia, eosinophilia
Laboratory Diagnosis
• Parasitological examination
--muscle biopsy
Deltoid or gastrocnemius muscles
are the best choice
• Immunodiagnosis
--ELISA
Detection of specific antibodies in serum
Epidemiology
Geographical distribution
• Cosmopolitan
The global prevalence of trichinellosis is
estimated as many as 11 million people may
be infected. More cases of human infection
have been found in developed countries than
in developing countries
Distribution of Trichinella spiralis in China
Source of infection
Pigs and other wild animals
containing the Trichinella larvae
Mode of infection
Ingesting the raw or improperly
prepared pork products
Treatment and prevention
• Albendazole / Mebendazole
• Development of industrialized pig farms
• Improvement of pig feeding
• Inspection of meat
• Health education
Filaria
Introduction
• Filariasis is a widely spread disease caused
by different species of filariae
• The adults of filariae inhabit the
lymphatics, subcutaneous tissue, deep
connective tissue, peritoneal or thoracic
cavity
• There are eight species of filariae, namely,
Wuchereria bancrofti, Brugia malayi,
Brugia timori, Loa loa, Onchocerca volvulus,
Mansonella ozzardi, Dipetalonema perstans
and Dipetalonema streptocerca in humans
• Larvae known as microfilariae appear in
the circulating blood or tissue fluids
• W. bancrofti and B. malayi which lie
coiled in the lymphatic vessels are
most commonly responsible for lymphatic
filariasis and of more medical importance
• Microfilariae circulate in peripheral blood
once each day. Mosquito is essential
vector and intermediate host
Classification
Phylum Nemathelminthes
Class Nematoda
Order Filariata
Family Dipetalonematidae
Wuchereria bancrofti
and Brugia malayi
Morphology -- Adult
• Slender, thread-like
• White in color
• Male -- 2.5-4 cm long and has a curved
tail, female -- 5-10 cm in length
Morphology -- Larva
• Microfilaria--177~296 µm in length, encased in
a sheath with free endings. Bluntly rounded
anteriorly and tapers to a point posteriorly. A
large number of nuclei seen in the body are
arranged in a column from head to the posterior
Wuchereria bancrofti
Brugia malayi
The morphological differentiation of
bancroftian and malayan microfilariae
W. bancrofti
Brugia malayi
Size
Larger, 244~296 by
5.3~7 µm
Smaller, 177~230 by
5~6 µm
Shape
Curves of body are
natural, smooth
Curves of body are
rigid, the small in
larger curve
Cephalic space
Shorter (length is equal Longer (length is two
to or less than width)
times as long as width)
Body nuclei
Equal sized, clearly
defined, countable
Terminal nuclei No
Unequal sized,
coalescing, uncountable
Two
Life cycle
Microfilariae
Peripheral blood
Microfilariae
Blood meal
Take off
sheath, migrate
to thoracic
muscles
Ovoviviparity
Adults
Molt 2
times
Sausage
larvae
Lymphatics
Infective
larvae
Molt
Molt
Migrate to prosbocis
Human stage
Blood meal
Infective
larvae
Mosquito stage
Characteristics of life cycle
• Host: mosquitoes as intermediate host,
human as final host
• Location: lymphatic vessels and lymph
nodes
• Infective stage: infective larvae
• Transmission stage: microfilariae
• Diagnostic stage: microfilariae
• Ovoviviparity
Characteristics of life cycle
• Different parasitic site between the two
species of lymphatic filariae: W. bancrofti
parasitizes in the superficial and deep
lymphatic systems, including in the
genitourinary lymphatic system; B. malayi
parasitizes in the shallow lymphatic system
only, especially in the lymphatics of limbs
Characteristics of life cycle
• Nocturnal periodicity: the numbers of
microfilariae present in the peripheral blood
during daytime is very low in density,
usually undetectable, but gradually increase
from evening to midnight and reach the
greatest density at 10 p.m. to 2 a.m.
• The mechanism for this phenomenon is still
not clear. It may be related to the change
of oxygen tension in cerebral and the
pulmonary vessels
Pathogenesis
• Results from a complex interplay of the
pathogenic potential of parasite, the immune
response of the host, and external bacterial
and fungal infections
• Acute diseases--dilatation of the lymphatics /
hyperplastic changes in the vessel endothelium
/ infiltration by lymphocytes, plasma cells and
eosinophils / thrombus formation
Pathogenesis
• Chronic lesion--the changes include granuloma
formation, fibrosis, and permanent lymphatic
obstruction
• Repeated infections eventually result in
massive lymphatic blockade
• The skin and subcutaneous tissues become
edematous, thickened, and fibrotic
• Dilated vessels may rupture, spilling lymph
into the tissue to cause lymphedema and
elephantiasis
Clinical manifestations
•
Asymptomatic amicrofilariaemic
•
Asymptomatic microfilariaemic
•
Acute manifestation
•
Obstructive (Chronic) lesions
Clinical manifestations
•
Asymptomatic amicrofilariaemic--in
endemic areas, a proportion of population
does not show microfilariae or clinical
manifestation even though they have some
degree of exposure to infective larva
similar to those who become infected.
Laboratory diagnostic techniques are not
able to determine whether they are
infected or free
Clinical manifestations
•
Asymptomatic microfilariaemic-considerable proportions are
asymptomatic for months and years,
though they have circulating
microfilariae. They are an important
source of infection. They can be
detected by night blood survey and
other suitable procedures
Clinical manifestations
•
Acute manifestation--during initial
months and years, there are recurrent
episodes of acute inflammation in the
lymph vessel/node of the limb & scrotum
that are consisting of filarial fever,
lymphangitis, lymphadinitis, epididymitis,
orchitis
Lymphangitis
Lymphoedema
Clinical manifestations
•
Obstructive (Chronic) lesions--takes 10-15
years, main pathological change is lymph
obstruction. The lymph circulation is disturbed
and lymphedema occurs. The affected limb
feels soft at first and becomes fibrotic after
extensive growth of connective tissue as
elephantiasis develops. e.g. hydrocoele
(40~60%), elephantiasis of scrotum, penis, leg,
arm, vulva, breast, and chyluria
Hydrocoele
Scrotum
Penis
Leg
Arm
Vulva
Breast
Chyluria and haematuria
Laboratory Diagnosis
• Microfilariae: demonstration of microfilarae in the
peripheral blood
a. Thick blood smear: 2~3 drops of free flowing
blood by finger prick method
b. Membrane filtration method: 1~2 ml intravenous
blood filtered through 3µm pore size membrane
filter
c. DEC provocative test (2mg/Kg): after consuming
DEC, mf enters into the peripheral blood in day
time within 30~45 minutes
• Adult: biopsy of the nodes or lymphatic vessels
• Immunological tests: antibody or circulating filarial
antigen (CFA)
Epidemiology
Geographical distribution
•
•
W. bancrofti is widely distributed throughout
the tropics and subtropics. It is prevalent in
Africa, Asia, and certain islands in the Pacific
Ocean
B. malayi has a distribution centering around
the Malay peninsula. In addition to Malaysia, it
occurs in India, Indonesia, New Guinea,
Thailand, Vietnam, Korea, Japan and China
Epidemiology
Global scenario
•
•
•
•
•
•
Population at risk: 1.2 Billion
No. of countries : > 80
Mf carriers: 76 Million
Diseased: 44 Million
Hydrocele: 27 Million
Lymphoedema: 16 Million
Treatment and prevention
• The source of infection should be eradicated
by mass survey and treatment
• All person with microfilariae should be treated
with diethylcarbamazine (DEC) which is the low
toxicity but most effective drug. 200mg tid
for seven days as one course. DEC added to
table salt (3:1000) and distributed in endemic
areas over a period of six months, results in
great reduction of microfilaria in the blood
stream
• Elimination of vectors and protection of the
people from mosquito bites are important to
control filariasis