Intestinal flagellateslecture no 5

Mrs: Dalia Kamal Eldien Mohammed

The Flagellates

The flagellates belong to the Mastigophora Subphylum and possess more than one flagellum.

Beating these flagella enable them to move. A cytosome may be present which helps in the identification of

the species. Flagellates possess one advantage over their amoeboid

relatives in that they can swim. Therefore, enabling them to invade and adapt to a wider range of environments unsuitable for other amoebae. They are able to change from a flagellated free-swimming environment to a non-flagellated tissue dwelling stage and vice versa.

The trophozoites are easily recognized in saline preparations by their motility. However, accurate identification is done on a stained fecal smear. Cysts are more commonly seen than the trophozoite.

There are pathogenic and commensal species of flagellates. The flagellates which are encountered in the intestinal tract are

Giardia lamblia Chilomastix mesnili Trichomonas hominis Retortamonas intestinalis Enteromonas hominis

taxonomy

Kingdom Animalia Subkingdom Protozoa Phylum Sarcomastigophora Subphylum Mastigophora Class Zoomastigophora Order Diplomonadida Family Hexamitidae Genus Giardia Species lamblia

Giardia lamblia

Is a flagellated protozoan parasite that colonizes and reproduces in the small intestine, duodenum and jejunum causing giardiasis

Worldwide distribution, common in tropics & subtropical countries. It is more common in warm climate .

It is the most common flagellate of the intestinal tract, causing Giardiasis.

Transmission:- Infection occurs by ingestion of cysts (generally from

fecal contaminated food or water)

Sources of infection: Contaminated water Contaminated food

 

Epidemiology

Giardia is most prevalent intestinal parasite. Has world wide distribution. Common in children 6-10 years age. Also prevalent in homosexual males. travelers or visitors to endemic areas. Primary immuno-deficiency (IgA deficiency) Recent increase in Giardia infection among

wilderness campers

Morphology Trophozoite: The trophozoites of G. lamblia are flattened pear shaped and

are an average size of 15 µm long, 9 µm wide and3 µm thick. When stained, the trophozoite is seen to have 2 nuclei, 2

slender median rods (axostyles), and 8 flagella arising from the anterior end.

They have been described as looking like tennis rackets without the handle (they are often seen has having a comical face-like appearance when looking at the front view)

The movement of the trophozoites are described as tumbling leaf motility

Trophozoite

Trophozoite

morphology

Cyst cysts are small, oval, 8-14 x 5-10 µm , thick cyst wall,

with four nuclei and fibrils and flagella longitudinally oriented.

The cyst environmentally resistant and responsible for disease transmission. (The infective stage of Giardia lamblia )

cyst

Life cycle

Definitive hosts are humans including a wide range of animals with no intermediate hosts or vectors

Giardia spp. have two stages, cysts and trophozoites. The infection is acquired by ingesting cysts. As few as 10-25 cysts are sufficient to establish an infection

in some humans. Trophozoites are released from the ingested cysts in the small

intestine. Trophozoites colonize the small intestine, attaching to the

mucosa of the bowel using a ventral sucking disks. The trophozoites then multiply by longitudinal binary fission

As the Giardia trophozoites move toward the colon, they retreat into the cyst stage (known as encystation) and the new cysts are excreted in the feces

Many of the dividing trophozoites are carried toward the colon, and encyst

Cysts can appear in the feces from 3 days to 3 weeks after infection

Clinical Disease Giardia lamblia colonies in the small intestine where the

trophozoites adhere to the mucosal surface by means of their sucking disc, and absorb their nutrients from the lumen of the small intestine causing Giardiasis.

Giardiasis does not spread via the bloodstream, nor does it spread to other parts of the gastrointestinal tract, but remains confined to the lumen of the small intestine

Cysts are produced as the parasites descend the intestinal tract although trophozoites can be passed in the faeces in severe infections.

Cysts can survive outside the body for several weeks under favorable conditions.

Symptoms

infection with Giardia lamblia can range from asymptomatic to severe diarrhea.

1-Asymptomatic infections: are responsible for the continued transmission of the parasite as

numerous cysts are produced. 2-symptomatic infections: Giardia lamblia generally does not penetrate the intestinal wall, but

may cause inflammation and shortening of the villi in the small intestine.

Extremely large numbers of trophozoites may be present and may lead to a direct, physical blockage of nutrient uptake, especially in fat soluble substances such as vitamin B12.

Symptoms include severe diarrhea, nausea and flatulence.

Laboratory diagnosis Giardiasis can be diagnosed by direct observation of the

trophozoites or cysts in the feces- several specimens- Trophpzoite: usually present in Water-like faeces Cyst: usually present in Formed faeces Duodenal fluid aspirate examination for chronic gardiasis For Fresh sample either do Saline wet mounts with or without

iodine or MIF (Merthiolate-iodine-formaldehyde) stain and permanently stained preparations (e.g., trichrome).

G. lamblia cyst

G. lamblia trophozoite

Immunodiagnosis (ELISA). Direct fluorescent antibody (DFA) assay. Culture system using Diamond medium. Molecular analysis by PCR-based assays.

Treatment

Giardiasis can be treated with a number of drugs, such as Metronidazole form 5-7 days or Tinidazole

Prevention control

Improving environmental sanitation Good hygiene, such as hand washing reduces the

risk of infection Boiling suspect water for one minute is the surest

method to make water safe to drink and kill disease-causing microorganisms such as Giardia lamblia if in doubt about whether water is infected