Tutorial MLS 602

Parasitology Topic 8 and 9

Overview of Topic 8 and 9

Interesting facts we have learnt Parasites occur in two distinct forms: single-celled protozoa and

multicellular metazoa called helminths or worms.Many protozoa have a life cycle consisting of a trophozoite, which is the

motile, feeding, reproducing form surrounded by a flexible cell membrane, and a cyst, which is the nonmotile, nonmetabolizing, nonreproducing form. The cyst form survives well in the environment and so is often involved in transmission.

Certain protozoa, such as Leishmania and Trypanosoma, have flagellated forms called promastigotes or trypomastigotes and nonflagellated forms called amastigotes.

More on Parasites

Many helminths have a life cycle that progresses from egg/ova to larva to adult. The egg contains an embryo that, upon hatching, differentiates into a larval form, which then matures into the adult form that produces the eggs.

A definitive host is one in which the sexual cycle occurs or the adult is present, and the intermediate host is one in which the asexual cycle occurs or the larva is present.

Harmful Effects of Parasites on Host?

Some Examples: Depriving the host of essential substance E.g

Mechanical damage of parasites on the host

E.g : Roundworms causing perforation and obstruction

Production of toxins E.g.

Causes inflammation and hypersensitivity reactions in host by production of

parasitic antigen that triggers the immune response of the host.

Trichomonas vaginalis

• Pear shaped flagellates, contains centric nucleus, 2 pairs of anterior flagella and one posterior flagellum. One undulating membrane that assist the protozoa to propel itself in a fluid environment.

• Loves acidic environment therefore mostly colonize female vagina. That’s why can’t survive in any other parts of the body.

Why males remain asymptomatic? Males are mostly carriers and it is a high risk because symptoms are not seen in males, so there is a

high chance his female partner during sexual contact can be infected.What type of specimens are received in the Lab for diagnosis? High Vaginal swabs or pap-smears.What are the likely symptoms seen in an infected female? The vaginal membranes are damaged by T. vaginalis whereby the flagellate starts eating away cell

fragments. This give rise to inflammation which results in frothy green discharge from the vagina. Chronic inflammation can lead to preterm labour and cervical cancer.

Invasiveness of Entamoeba histolytica

• Infection from ingestion of ameobic cysts from soil, unwashed vegetables, contaminated water/food, fecal oral route etc.

• Passes through the stomach and once in small intestine it transforms cystic form to trophozoites.

• Trophozoites invade into the mucosa of the large intestine causing damage to the tissue cells. Once the tissues are damaged it increases secretions. Eventually the mucosa lining becomes perforated and small ulcers are formed. Some causes peritoneal cavity infection and other are passed through bloody diarrhea.

• Few trophozoites enters the blood stream and travel up to the liver that latter causes liver abcesses.

What do Amoeba do?

• Able to secrete proteinases that destroys proteins of the host• Destroy intestinal cells (perforation and ulcer formation) through

direct contact mechanism• Ability of Amoebapore formation which forms pores in lipid

bilayers of the infected cells which leads to lysis of cells• Increases intestinal permeability.How is Amoeba diagnosed in the lab?Stool microscopyLiver abscess microscopy

Giardia lamblia

• Intestinal flagellate• Trophozoite “Cross eyed Tennis Racket” shape.• Consists of two nucleus, 2 ventral sucking disc, parabasal body, 8

flagella.• Cysts has 2 to 4 nuclei in the cytoplasm. • Specimen type is stool.• Effects on humans are abdominal cramps, pain and dysentery.

Chronic giardiasis can cause Vitamin B12 deficiency and lactose intolerance.

Hemoflagellates; Trypanosoma species

• American Trypanosoma causes ‘Chagas diseases”- Trypanosoma cruzi• Transmitted through the faeces of triatominae/reduviid bugs • Also known as ‘kissing bug” because it typically bites people on the face as

they sleep.How it infects? Need to understand what stages are found in both hosts. Epimastigote (contain flagellum)- found in lumen of bug Trypomastigote- enter human host after a blood meal and invade human

cells. Amastigotes- aflagella multiples intracellarly through binary fission.Lets look at its life cycle?

Life cycle simplified

The infected bug takes a blood meal and after sucking blood it defecates. This will expose the site of the sting and trypomastigotes enter though the bite

Trypomastigotes starts invading the inoculated cells. Once inside the cell it transforms into amastigotes which starts to multiple by binary fission.

Once large number of amastigotes are formed, it starts to develop its flagella and try to escape out of the cell. This pressure applied by transformed trypomastigote cause cells to lyse and are release in the blood stream.

Once in the blood stream the trypomastigotes travel through blood to other organs and lymphatics. The cycle continues as another bug takes a blood meal. Acute infection involves fever and inflammation and chronic infection leads to cardiac muscle damage, nerve cell damage and megacolon.

How do you test in the lab? Leishman and Giemsa stained blood smears DNA- Polymerase Chain Reaction Serological tests- Antigen and antibody test for T.cruzi

African Trypanosomiasis

Also known as sleeping sickness Caused by Trypanosoma brucei rhodesiense which is transmitted by tsetse bug. The life cycle is similar to T.cruzi but few differences are the vector, parasites enter lymphatic system

and then pass into the blood stream. Then it is able to enter the spinal fluid and causes mental deterioration and other neurologic

problems progresses more slowly and with 1-2 years central nervous system involvement, with personality

changes, daytime sleepiness with nighttime sleep disturbance, and progressive confusion. Other neurologic signs, such as partial paralysis or problems with balance or walking may occur, as well as hormonal imbalances.

The is a dark Giemsa-staining structure which is distinct from the nucleus. Contains mitochondrial DNA and is closely related to cell morphologies during trypanosome cell cycle. Each daughter cells receive identical kinetoplast.

Naegleria fowleri

• Free-living amoeba• Produces an acute, and usually lethal, central nervous system (CNS) disease called primary

amoebic meningoencephalitis (PAM).• Interesting characteristics- When deprived of nutrients, the trophozoite transforms into

flagellate state. This form is usually pear shaped with two flagella emerging from the narrow portion. The flagellate form does not divide or feed. It will revert back into the amoeboid form when nutrients are restored. When conditions become adverse, such as diminished food supply or colder temperatures, the trophozoite transforms into a resistant cyst stage. It is the trophozoite stage that is infective.

Tests done?CSF analysis to check for amoeba and flagellates

Leishmaniasis- Another Haemoflagellate

• vector borne disease that is transmitted by sand flies and a rare disease• L. donovani, L. mexicana , L. tropica; L. major; L. aethiopica. There are

about 20 species• cutaneous leishmaniasis, which causes skin sores and ends up as skin

ulcers• visceral leishmaniasis, which affects several internal organs (usually

spleen, liver, and bone marrow) and can be life threatening.• Mucosal leishmaniasis- spread from the skin and cause sores in the

mucous membranes of the nose (most common location), mouth, or throat.

Life Cycle

• Sand fly injects promastigotes into the skin during a blood meal (infective stage)

• Promastigotes are phagocytized by neutrophils that are recruited at the bite site.

• Infected neutrophils release the parasites which are then consumed by macrophages.

• Inside macrophage, promastigotes transform into amastigotes (diagnostic stage).

• Amastigotes multiply in macrophages and finally cell bursts and release in the blood.

Sporozoan Topic 9

What we know about Sporozoa?

Lack locomotion

Obligate intracellular protozoa

Complicated life cycle: sexual and asexual phase.

Have intermediate and definitive host

Sexual-sporogony and Asexual is Schizogony

The sporozoites have apical complex. This structure is used for attachment to the host.

Differentiate between schizogony and sporogony.

Schizogony- multiple fission/ budding production of merozoitesand production of male and female gametes.

Sporogony- production of sporozoites

Toxoplasmosis

Caused by Toxoplasma gondii Definitive host are feline (cats) Unsporulated oocysts tachyzoites bradyzoites Transplacentally from mother to fetus, consuming contaminate food/water, blood

transfusion and organ transplantation.Lab Diagnosis Serology- TORCH is panel of tests for detecting infections in pregnant women. Testing IgG

antibodies for congenital infections. IgM antibody or rising titers of IgG antibody can confirm a diagnosis of specific infection. The presence of IgM-specific antibody in cord, fetal, or neonatal blood indicates congenital infection.

stained biopsy specimens- tissue cyst T. gondii DNA in amniotic fluid using molecular methods such as PCR

Malarial Parasite

Name the four main species of Plasmodium that cause Malaria?P.ovale, P. falciparum, P.vivax and P.malariaeVector borne disease- Female Anophele mosquitoes Incubation period can be from 7 to 30 days. It has a cyclic pattern of infection. In humans, the parasites grow

and multiply first in the liver cells and then in the red cells of the blood. In the blood, successive broods of parasites grow inside the red cells and destroy them, releasing daughter parasites (“merozoites”) that continue the cycle by invading other red cells.

Life cycle

Distinguish different species using Laboratory Features

What all to learn?

• GRASP (Know Very Well)

Morphology and life cycles of parasites

• Familiarize (Know well)

Pathogenesis and Laboratory Diagnosis of parasitic infections

• Understand (Know)

Prevalence, prevention and control of parasitic diseases