Balantidium coli and Leishmania donovani

Balantidium Coli

Distribution:

It is worldwide in distribution

Habit and habitat:

It is a monogenetic parasite. It is found in the large intestine of man.50 species of Balantidium is recorded but Balantidium Coli is the only species which infect human.

Morphology:

It consists of two types i.e trophozoite and cyst

Trophozoite

The trophozoite is largely covered with a delicate pellicle which gives it a fixed shape. The whole body is covered by a uniform size,short cilia but at the part, the cilia are slightly longer called amoral cilia. Cytoplasm consists of two contractile vacuole and many food vacuoles. At the posterior end of the body pore or cytosine is present where undigested food is thrown out. Trophozoite has two nuclei a large kidney shaped macronucleus which controls the metabolic activity of the body and smaller is micronucleus which controls the reproductive activity of the body.

Cyst

A cyst is slightly smaller in size than trophozoite. It is surrounded by a thick transparent double layered cyst wall. It contains the granular cytoplasm with macronucleus, micronucleus and food vacuoles.

Lifecycle

Balantidium Coli is a monogenetic parasite. The natural host is the pig but sometimes accidently host as the man. The man is infected by ingesting contaminated food, contaminating cyst of Balantidium.The Balantidium reaches to the alimentary canal of man due to the action of the digestive enzyme, the cyst wall rupture and releases trophozoite. The trophozoite is an active, growing and feeding stage of the parasite. The trophozoite shows two types of reproduction;

Asexual reproduction by binary fission and

Sexual reproduction by conjugation

During binary fission, the micronucleus divided mitotically into two and macronucleus divided amitotically into two.Finally, body divide into two daughter ciliates. During conjugation two trophozoites are enclosed in a cyst of exchange of micronucleus takes place and then separate to form two individuals.

Pathogenesis

• It causes a disease balantidiasis.Symptoms are
• Balantidial dysentery was frequently passage of stool with blood mucus.
• Vomiting

Treatment

Metronidazole is effective drug

Prophylaxis

• Proper disposal of sewage
• Wash hand with antiseptic soap
• Avoid eating unhygienic food.
• Use boiled water
• Make environment clean

Leishmania donovani

Distribution: Leishmania is identified by British medical officer sir William Leishman. Three species of Leishmania infect man. Leishmania donovani causes a serious disease called kala-azar. It is transmitted by the sandfly. It is widely distributed in Asia, Africa, and South America

Habit and habitat:

Leishmania donovani is a digenetic parasite. It required two hosts to complete its lifecycle ie. Man and sandfly. In man, it is found in the reticuloendothelial system such as intestinal mucosa, liver,spleen,bone marrow etc. In sandfly, it is found in the alimentary canal and buccal cavity.

Morphology

The parasite exists in two form ie

Amastigote stage or Leishmanial form (found in human)

Promastigote forms in sandfly

Leishmania donovani is a flagellated parasite that occurs in two forms. The two forms are leptomonad and lesmenial form. Leishmanial form occurs in the body of vertebrates host. The leishmanial form is also known as amastigote that lives intracellularly in the blood cell or reticule-endo epithelial cells of man. It has rounded or oval shape nucleus lies towards the periphery in the cytoplasm. The outer part in the cytoplasm are blepharoplast and kinetoplast. It has no free flagellum and measure s2-4 [micro] in diameter.

The leptomonad form is found in the midgut of the sandfly. It is elongated and slender in shape with large centrally located nucleus.It has blepharoplast and kinetoplast in the cytoplasm and along free flagellum.It measures 15-20[micro]in length and 1-2 in width.The outermost covering is cell membrane which is covered by thin elastic and delicate pellicle that gives firmness to the body. It is uniflagellate the flagella arises from blepheroplast which is long in the leptomonad form but greatly reduces in the lesminal form. The cytoplasm is colourless and homogeneous. It consists organelles like Golgi bodies kinetosome rizoplast mitochondria vacuoles and nucleus. Leishmania is uninucleated nucleus is either peripheral or lies at the centre of the body.

Lifecycle

Lifecycle completes in two hosts ie digenetic parasite (two genetic species)

Primary or final host (sexual and adult cycle complete ) :man and other vertebrates host.

Secondary host or intermediate host: sandfly

Lifecycle:

Leishmania is digenetic. Its hosts are man and sandfly. The man is the principal host in which parasite feeds and multiply asexually. The secondary host is sandfly acts as a vector. Other mammals like dogs, jackals, and ground squirrels also serve as reservoir host in which the parasite does not undergo any change but it just waits for its introduction into the human host.

Infection to the man

It occurs when sandfly bites a man. The actual transfer is not known the spread of infection may occur by being crushed or by slapping.The parasites introduced in man’s body is in promastigote form. This form enters the reticuloendothelial system and changes into amastigote form. This undergoes slow multiplication by longitudinal binary fission so that host cells become greatly enlarged.

Spread of infection

The host cell rupture when the number of amastigote form reaches 50-20. The liberated parasite takes up the new cell and repeats the multiplication cycle. Some of the amastigotes are engulfed by the neutrophils and monocytes and this heavily parasitized cell wonder through the general blood circulation leading to the general infection.

Transfer to sandfly

When sandfly sucks the blood of infected person it obtains amastigote forms along with blood meal.

Development in sandfly

In the midguts of the sandfly, the amastigote forms progress to promastigote form and multiply by longitudinal binary fission. Within 6 to 9 days, the number of parasites becomes enormous and spread into the pharynx and buccal cavity. Transmission into new host occurs when infected sandfly bites the man.

Symptoms and pathogenesis

The incubation period is 3-6 months but symptoms may appear in every two years. The early symptoms include swelling,high fever, enlargement of spleen and liver. Which follows weakness anaemia, emaciation darkening of the skin. In the advanced stage, skin becomes rough, dry and dark hair becomes brittle. Patient dies within 2 years if not treated, death is generally due to secondary infection as the immune system becomes weak.

Diagnosis of Leishmania infection

The infection is diagnosed by microscopical examination of blood film or biopsy of spleen and liver of patient for the presence of amastigote form.

Treatment

The treatment includes antimony compounds like sodium antimony, tartrate and gluconate urea stibine and neustibasian, prophylaxis includes eradication of insects vector attack on parasite and personal defence.

References

Arvind, Keshari K. and Kamal K Adhikari. A Textbook of Biology. Vidyarthi Pustak Bhander.

Michael J.Pleczar JR, Chan E.C.S. and Noel R. Krieg. Microbiology. Tata Mc GrawHill, 1993.

Powar. and Daginawala. General Microbiology.

Rangaswami and Bagyaraj D.J. Agricultural Microbiology.