Transcript Blood and Tissue Nematodes of Human Beings

Blood and Tissue
Nematodes of Human
Beings
FILARIAL PARASITES OF
HUMAN BEINGS
Filariae
• The slender filarial worms of the family
FILARIIDAE are arthropod-transmitted
parasites of the circulatory and lymphatic
systems, muscles, connective tissues, or
serous cavities of vertebrates.
• Principal species in humans are:
Wuchereria bancrofti, Brugia malayi,
Onchocerca volvulus, Loa loa,
Dipetalonema perstans and Mansonella
ozzardi.
• A distinctive feature filarial worms is that
the viviparous female gives birth to
prelarval microfilariae.
Wuchereria bancrofti and Brugia
malayi
CLASS: SECERNENTEA
SUBCLASS: SPIRURIA
ORDER: SPIRURIDA
SUPERFAMILY: FILARIOIDEA
FAMILY: FILARIIDAE
Scientific name - Wuchereria bancrofti
Disease - filariasis, elephantiasis
Scientific name - Brugia malayi
Disease - filariasis, elephantiasis
Life Cycle of Wuchereria bancrofti:
A microfilaria of Wuchereria bancrofti as it would
appear in a blood smear; approximate size =
200 µm in length.
Elephantiasis of Legs and Scrotum
Elephantiasis of the legs
• Historical
Elephantiasis has been written about since
the time of the early Greeks and Romans.
• Hosts
humans.
• Distribution
Tropical or subtropical (41N. latitude to
31S. latitude). South America, Cuba,
Puerto Rico, West Indies, Africa, Spain,
Turkey, Asia, Australia, many South Pacific
Islands.
• Characteristics
Adult worms are long and slender with a
smooth cuticle and bluntly rounded ends.
The head is slightly swollen and bears two
circles of well-defined papillae. The mouth
is small; a buccal cavity is lacking. The
male is about 40 mm long and 100 um
wide. Its tail is fingerlike. The female is 6
to 10 cm long and 300 um wide. The vulva
is near the level of the middle of the
esophagus.
Symptoms-Pathogenicity
• Four stages of the disease are recognized.
• The incubation period of 3 to 12 months in
which there are no symptoms.
• The acute symptomatic stage in which
some swelling of the extremities may
occur and this may be accompanied by
pain, weakness of arms and legs,
headache, insomnia. Fever is usually not
present.
• There is a period of recovery which is
permanent if reinfection does not occur.
• If there is continued reinfection the cycle
repeats and elephantiasis may result.
• The worms in the lymphatic system cause
tissue changes which restrict normal flow
of lymph and result in swelling, fibrosis
and eventually secondary infections in the
affected tissues. The lower extremities and
groin are the parts most likely to be
affected. The adult worms live for several
years.
Onchocerca volvulus
•
• Human onchocerciasis is caused by the filarial
parasite Onchocerca volvulus whose life cycle
occurs in two different hosts: black flies, and
human. The infective larvae (a: stage L3) are
normally transmitted by the bite of Simulium
flies. Once in the human body, the larvae
undergo molting to stage L4 (e), to then reach
the adult stage in about one year (f). Adult
female are able to produce millions of
microfilariae (h) that they shed in the blood of
their human host. When female blackflies take a
bloodmeal they ingest those microfilariae that
are going to undergo in the fly host a first
transition to L2 life stage (j). L2 larvae then molt
to L3 (a), the infective stage for human.
• Simulium flies breed in fast flowing rivers i.e well
oxygenated water, because their larvae have an
obligatory aquatic stage during which they
require high oxygen tension (see picture below).
Hence, Onchocerciasis is associated with fast
flowing rivers including rapids. That's why the
blindness Onchocerciasis can lead to is often
referred to as 'river blindness'.
• The infective larvae of Onchocerca (stage L3)
enter the body through the wound made by the
bite of its host fly. The larvae then move to the
subcutaneous tissues where they become
encapsulated within nodules and mature into
adults in approximately one year
• After mating the female sheds microfilariae 300
mm in length and 0.8 mm in diameter. The
microfilariae are sheathless with sharply pointed,
curved tails.
•
• The microfilariae can be found free in the fluid
within the nodules and in the dermal layers of
the skin spreading away from the nodules
containing the adults. Microfilariae also can be
found in the blood and eye during heavy
infections. They infect their fly vectors while the
flies are feeding on the human host and mature
into third stage infective larvae in the flies' flight
muscles (about 10 days total).
Loa loa
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CLASS: SECERNENTEA
SUBCLASS: SPIRURIA
ORDER: SPIRURIDA
SUPERFAMILY: FILARIOIDEA
FAMILY: ONCHOCERCIDAE
Scientific name - Loa loa
Common name - eye worm
Disease - loaisis, fugitive or Calabar
swellings
• Hosts: Humans
• Distribution: Rain forest areas of west Africa
and equatorial Sudan
• Life Cycle: Adults live in subcutaneous tissues.
The microfilariae are periodic, appearing in the
peripheral blood in maximal numbers during
daylight hours and concentrating in the lungs at
night. The intermediate host is the deer fly
Chrysops. The nematodes develop to the thirdstage, filariform juveniles in the fat body of the
fly, after which they migrate to the mouthparts.
The prepatent period in humans is about a year,
and adult worms may live at least 15 years.
• Characteristics
• Simple head with no lips and eight cephalic
papillae; a long, slender body; and a blunt tail.
The cuticle is covered with irregular, small
bosses, except at the head and tail. Males are
20 to 34 mm long by 350 to 430 um wide. The
three pairs of preanal and five pairs of postanal
papillae are often asymmetrical. The spicules
are uneven and dissimilar, 123 and 88 um long.
Females are 20 to 70 mm long and about 425
um wide. The vulva is about 2.5 mm from the
anterior end, and the tail is about 265 to 300 um
long.
• Symptoms-Pathogenicity
Adults have a tendency to wander through the
subcutaneous connective tissues. When they
are still, the host reaction results in localized
"Calabar swellings", which disappear when the
worm moves on. Adults also migrate through
the conjuctiva and cornea with swelling of the
orbit and psychosomatic results to the host.
• Management
Diagnosis is by demonstration of microfilariae in
the blood. Surgical removal of swellings.
Chemotherapy as in bancroftian filariasis.
Control of deer flies is difficult.