Department Of Zoology
Tariq Gul
Class Ist Year
Topic :- life Cycle and Pathogenecity of Wuchereria bancrofti
Wuchereria bancrofti
Introduction of Wuchereria bancrofti
Wuchereria bancrofti also called as filarial worm belongs to the phylum nematode.
It is a dreadful human parasite found in the lymph glands and lymph passages and
blood of man. The parasite shows sexual dimorphism as male (smaller) and female
(larger) individuals are separate. It is worldwide in distribution except Polar
Regions.
Life cycle of wuchereria bancrofti
Hosts: Wuchereria bancrofti is a digenetic parasite, as it completes its life cycle
in two hosts. Primary host or principal host or final host is man, in which it lives
in lymph glands and lymph passages and blood. The secondary host or
intermediate host or vector host is an invertebrate or blood sucking insect usually
a mosquito.
(A) Life cycle in man:
(1) Infection of man: When an infected mosquito bites a man, it liberates the
parasites in the skin wound caused by its proboscis. The mosquito liberates both
male and female Juveniles (young ones) in the human body.
(2) Copulation: Copulation takes place when individuals of both the sexes (male
and female) are present in the same lymph gland.
(3) Larval development in Man: Female is viviparous (probably ovoviviparous),
which releases numerous Juveniles called microfilariae. They are born in an
immature state, they are in fact embryos rather than Juveniles. They are
microscopic, about 0.2 to 0.3 mm long and are surrounded by a delicate circular
sheath (membrane) and containing rudiments of various adult structures. The outer
body surface of microfilariae is covered by flattened epidermal cells and on inner
side a column of cytoplasm is present which contains many nuclei. Important
structures from anterior end to posterior end are, future mouth or oral stylet, nerve
ring band, nephridiopore, renette cell, darkly staining inner mass, four large cells
and future anus. Microfilariae which are discharged into the lymph vessels soon
enter blood vessels and circulate with blood showing active movements. They
migrate to reside ultimately in deeper blood vessels of thorax. But they do not
undergo further development until sucked by the intermediate host, i.e. mosquito.
Microfilariae in human blood finally die unless ingested by the intermediate host.
(4) Development in Mosquito: In the stomach of mosquito microfilariae lose their
sheath and penetrate the stomach wall and migrate to thoracic muscles or wing
muscles, where they undergo metamorphosis and grow. During growth they first
change into a plump sausage-shaped organism (fatty meat piece) of about 150250µ long. Then they change into a more elongated form, and finally to form a
long slender shaped juvenile of third infective stage. Microfilariae undergo two
moults in about 10 days to reach the third stage larvae which are about 1.5 mm
long. Infective juveniles now migrate into mosquito’s labium (proboscis).
(5) Infection of new human host: When this infected mosquito bites a potential
human host by its proboscis, the infective juveniles come out of its labium and get
entered into the skin wound made by mosquito. In new human host, juveniles pass
into lymph glands and lymph passages, where they coil up and develop into adult
forms. Adults copulate and the females deliver (give birth) microfilariae.
PATHOGENECITY OR DISEASE OF Wuchereria bancrofti
Filariasis or Elephantiasis
(1) Occurrence: Filariasis disease is found throughout the World. Its causative
agent is a nematode called Wuchereria bancrofti. The nematode lives in the
lymphatic system of man, where they obstruct the flow of lymph, causing a severe
condition known as elephantiasis. In this disease, the limbs or other body parts
grow to enormous size.
(2) Symptoms: The incubation period of this disease is long and the symptoms
may appear after 8-16 months. Light infection produces no serious symptoms. It
causes filarial fever, mental depression, headache, etc. In heavy infection,
accumulation of living or dead filarial worms finally blocks the lymphatic vessels
and glands, resulting in various pathological conditions. Most spectacular is the
immense swelling of the affected body parts known as elephantiasis or filariasis.
Due to lymphatic obstruction, lymph cannot move back into the circulatory system
and accumulates into organs and causes these organs to swell or enlarge to a
greater extent (lymphedema). Generally lower limbs, scrotum in males, legs and
mammary glands are affected. There occurs inflammation of lymphatic vessels
(lymphangitis) and lymphatic glands (lymmphadentis).
(3) Diagnosis: The disease can be diagnosed by the study of microfilariae after
staining. Microfilariae of different species are identified after their specific shape
and morphological characters.
(4) Treatment (therapy): For the treatment of filariasis, some drugs are used. The
effective drugs used are heterazan, compounds of antimony and arsenic, cyanine
dyes, diethylcarbamazine citrate, etc. These drugs destroy microfilariae from the
circulation. Large swellings can be removed by surgery.
(5) Prevention (Prophylaxis or control): Preventive measures are as under:
(a) Destruction or Eradication of insect vector i.e. mosquito. In endemic areas,
small trees and bushes should be cleared off.
(b) Use mosquito repellent cream on exposed parts of the body.
(c) Periodic fumigation and spray of insecticides of sleeping rooms should be done.
(d) The mosquito nets or screens should be used for preventing ourselves from the
bite of mosquito and avoid sleeping on ground floors.
(e) Do not keep stagnant water in the surroundings as these pools of water are their
breeding places.
(f) Wear clothes with long sleeves, full length pants and socks for proper
protection.
CANAL SYSTEM IN SPONGES
A distinguishing feature (important feature) of all sponges is that their body
surface is perforated by numerous apertures for the entrance and exit of water
current. Inside the body, the water current flows through certain system of spaces
(canals) collectively forming the canal system.
TYPES OF CANAL SYSTEM
The arrangement and complexity of internal channels (spaces) vary considerably in
different sponges. Accordingly, the canal system has been divided into three types,
I.e. Ascon type, Sycon type and Leucon type.
(1) ASCON TYPE (ASCONOID CANAL SYSTEM)
It is the simplest type of canal system which is found in Leucosolenia (asconoid
sponge). Its (sponge) body surface is perforated by a large number of minute pores
called incurrent pores or ostia or dermal ostia. These pores are intracellular spaces
within tube like cells called the porocytes. These pores (ostia) open directly into
the spongocoel (large central cavity). The spongocoel is the single, large central
cavity in the sponge body and is lined by the flagellated collar cells or
choanocytes. Spongocoel opens to outside through a narrow circular opening
called the osculum, which is located at the free distal end. Surrounding sea water
enters the canal system through ostia. Flow of water is maintained by the beating
of flagella of collar cells or choanocytes.
Passage of water current in the body of sponge may be shown as under:
Outside water
through Ostia
Spongocoel
through Osculum
Ascon type
To Outside
(2) SYCON TYPE (SYCONOID CANAL SYSTEM)
Sycon type of canal system is more complex than Ascon type. It is found in sycon
and Grantia (syconoid sponge). It can be theoretically derived from the ascon type
by horizontal folding of its body wall. Body wall of syconoid sponges includes two
types of canals, incurrent canal and radial canal. Both types of canals are
interconnected by minute pores. Ostia found on the outer surface of the body open
into the incurrent canals. These incurrent canals are non-flagellated, as they are
lined by pinacocytes and these incurrent canals opens into radial canals through
minute openings (pores) called prosopyles. Radial canals are flagellated channels
as they are lined by choanocytes (flagellated collar cells). These radial canals open
into the spongocoel by small pores called apopyles. The spongocoel is a narrow,
non-flagellated cavity lined by pinacocytes and it opens to the exterior through an
excurrent pore called the osculum.
Passage of water current in the body of sponge may be shown as under:
Outside water
Ostia
Incurrent canals
Prosopyle
Radial canals
Sycon type
Apopyle
Spongocoel
Osculum
To Outside
(3) LEUCON TYPE (LEUCONOID CANAL SYSTEM)
This canal system is most complex type of canal system and is found in leuconoid
sponges such as Spongilla. It is formed due to further folding of body wall of
Sycon type, especially radial canals of sycon type, which form flagellated
chambers. This type of canal system has become irregular and often branched.
Flagellated chambers are small, spherical and are lined by choanocytes (flagellated
collar cells) and these flagellated chambers are formed due to folding of radial
canals. All other spaces are lined by pinacocytes. Incurrent canals open into
flagellated chambers through small pores called prosopyles. Flagellated chambers
open into excurrent canals through another small pore called apopyles. These
excurrent canals are developed as a result of shrinkage and division of spongocoel
which has disappeared and these excurrent canals open to the outside through an
osculum.
Passage of water current in the body of sponge may be shown as under:
Outside water Ostia Incurrent canals prosopyle Flagellated chambers
canals
Apopyle
Excurrent
Osculum
To Outside
Leucon type
Leucon type of canal system has three grades such as Eurypylous type, Aphodal
type and Diplodal type.
(a) Eurypylous type: It is the simplest and most primitive Leucon type of canal
system. In this type, the flagellated chambers opens directly into the excurrent
canals by broad apertures called the apopyles e.g. Plakina.
(b) Aphodal type: In this type, the flagellated chambers opens into the excurrent
canals by a narrow canal (pore) called the aphodus e.g. Geodia.
(c) Diplodal type: In this type, besides aphodus, another tube (canal) called as
prosodus is present between incurrent canal and flagellated chamber e.g.
Spongilla.
FUNCTIONS OF CANAL SYSTEM
The canal system helps the sponge in nutrition, respiration, excretion and
reproduction. The water current flowing through the canal system brings food and
oxygen and carries away faeces, nitrogenous wastes and carbon-dioxide. It also
carries spermatozoa from one sponge to another sponge for the fertilization of ova
there.