Giardia lamblia and the malarial parasites

Giardia lamblia

It is world wide in distribution and found in the duodenum and upper part of in jejunum.

Morphology:

Exist in two phases-trophozoite and cysts

• Trophozoites:The shape of trophozoites is that like of tennis or badminton racket.The dorsal surface is convex while ventral surface is concave having a sucking disc.The anterior end is rounded and broad.while the posterior end is pointed.It is bilaterally symmetrical and all the organs of the body are paired.thus there are two axostyles,two nuclei and four pairs of flagella.The size of trophozoites is 14µm long and 7µm in wide.
• Cysts:The fully formed cysts is oval in shape and measures 12µm×7µm.The axostyle lies more or lies diagonally.There are four nuclei.The remains of the flagella and the margin of the sucking disc may be seen inside the cytoplasm.

Life cycle:

Pathogenesis:

The pathogenesis of Giardia is not completely understood.Giardia is spread via the faecal-oral route.The cyst may be ingested with contaminated food or water or acquired from unwashed hand.Giardia cysts are quite resistant to chlorination.Humans are the main reservoir forGiardia lamblia.But other species may found in animals.

The incubation period for infection is generally 9-15 days.G.lamblia is present within duodenum,jejunum mucosa but doe snot invades the tissue.The parasite attaches itself to the epithelial surface of duodenum and jejunum by means of sucking disc.It may cause disturbance of intestinal function leading to mal-adsorption of fat.The parasite is also capable of producing harm of its toxic and irritating effect.The clinical illness caused byGiardia lamblia is commonly called Giardiasis.

The major symptoms of acute giardiasis are fleeing of intestinal uneasiness followed by nausea,anorexia,low-grade fever, and chills.These symptoms are followed by watery,foul smelling explosive diarrhoea,abdominal pain,mild steatorrhoea anaemia and weight loss may be seen.

Lab diagnosis

Guardians can be diagnosed by identification of cyst,trophozoites or both in faeces

1. Microscopic examination:For the demonstration of giardia cysts and trophozoites wet mount preservation is useful.
2. Interest:The trophozoites ofG.lamblia may also be detected in a duodenal fluid.A useful method for obtaining the duodenal specimens is the interest.In this text, the patient is asked to swallow a gelatine capsule which contains a nylon thread at one end.The free end of the nylon thread is attached to the chick of a patient.The capsule passes through the stomach to the duodenum.In the stomach, the capsule is dissolved and thread remains in the duodenum and the jejunum.After 2 hours the thread is withdrawn and placed in a tube containing saline.The centrifuged deposit of the saline is examined microscopically for motile trophozoites of G.lamblia.

Sexology

Fluorescence Antibody test(FAT) and ELISA have been developed for detection ofGiardia lamblia antigen in faces.However, these are not in routine use.

The malarial parasites

The malarial parasites of man belong to plasmodium genus.The parasites possess a life cycle which shows an alternation of generation of generation accompanied by an alternation of the host.There are four species recognized in man

1. Plasmodium malaria
2. Plasmodium vivax
3. Plasmodium falciparum
4. Plasmodium ovale

The malarial parasites are found in all countries.The tropical is the endemic home of all malarial parasite.P.vivax is the prevailing species of the temperate zone. Development of malarial parasite takes place in the liver cell then residue in the RCB and are carried by the circulatory blood to all the organs.

Life cycle

The malarial parasites posses its life cycle in two different hosts they are diagnostic.

Human cycle: Asexual cycle takes place in human called schizogony.Hence man represents intermediate host.It comprises following stages

• Pre-erythrocytic schizogony
• erythrocytic schizogony
• Gametogony schizogony
• Exoerythrocytic schizogony

There are mainly two phases of development in the human host.

1. Inside liver(Tissue phase or exoerythrocytic cycle)

• Pre-erythrocytic schizogony:No clinical symptoms and no pathological damage.
• Exoerythrocytic schizogony:Cause of relapse(recurrent)

In RCB(Erythrocytic phase):

• Erythrocytic schizogeny:Cause of malarial paroxysm(cold,hot,sweating)duration 6 hours
• Gametogony:Infect mosquito.

Mosquito cycle

Female anopheline mosquito both sexual cycle and asexual takes place in mosquito hence are the definite host.Mosquito remains unaffected.

Pathogenesis

• Reservoir of infection:Man acts as the only reservoir of infection in endemic area in some part of Africa chimpanzees may act as reservoir for P.malaria
• Mode of infection:Female anopheles mosquito acts as transmitting agent.The infection is transmitted by the inoculative method.

Infective form-sporozoites

portal of entry-skin

the site of localization-first in the liver cell than in RCB

Other modes may be transfusion and congenital

Infection:Infection withPlasmodiumcauses intermittent fever which is known as malaria.Each species causes characteristics feature

• P.vivax-Bonign tertian
• p.falciparum-malignant tertian
• p.malariae-Benign quartet
• p.ovale-Benign tertian

Incubation period:In P.vivax,P.ovaleandP.falciparum.It is 10 to 14 days and inP.malariaeit is 15 days.

Clinical features:Infection may result in varieties of symptoms ranging from mild symptoms to several diseases and even death.

Lab diagnosis

• Examination of parasites:Microscopic examination of thick and thin blood film.It is the definitive method of diagnosis of malaria thin blood film is useful for identifying specific species and thick blood film is useful for detection of parasites.
• Rapid diagnostic test:Rapid diagnostic text is based on detection of antigen using the immuno-chromatographic method.This is based on detection of monoclonal antibody againstP.falciparum histidine-rich protein.This test takes about 15 minutes thus are rapid.Parasitic lactase dehydrogenase for all four Plasmodium species can also be detected using rapid test.
• Serology:Indirect fluorescent antibody(IFA)indirect haemagglutination(IHA)and ELISA test are use for diagnosis of malaria

Preservation and control

• Mosquito control:The spraying of the indoor,surface of the house with insecticides is most effective measure kill the adult mosquito.
• Larval control:larvesides such as temephos may be use to reduce larva.
• Source reduction:Management of water level reduce mosquito breeding site.

References

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

Gupta, P.K. Genetics. New Delhi.: Rastogi Publications.

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.