BLOOD AND TISSUES – TOXOPLASMA GONDII

BLOOD AND TISSUES – TOXOPLASMA GONDII

Definition

• Toxoplasma gondii is a protozoan parasite that infects almost all warm-blooded animals, including humans.

Causes

• The parasite has a complex life cycle that involves two main hosts: definitive hosts (cats) and intermediate hosts (humans, animals, and birds).
• The parasite is usually transmitted to humans through contact with contaminated cat feces or undercooked meat (lamb, beef, and pork).

Types

• There are three main types of Toxoplasma gondii:

1. Type I: This type causes severe symptoms in immunocompromised individuals.
2. Type II: This type is the most common and usually causes mild symptoms in healthy individuals.
3. Type III: This type causes symptoms in immunocompromised individuals similar to Type I.

Pathogenesis

1. → Ingestion of oocysts (eggs) from contaminated cat feces or undercooked meat.
2. → Trophozoites (young parasites) invade the intestinal epithelial cells.
3. → The trophozoites multiply and transform into tachyzoites, which then invade other tissues.
4. → The immune system responds with an inflammatory reaction, which may lead to tissue damage and scarring.
5. → The parasite can form cysts in muscles and brain tissue, where they remain dormant for years.
6. → Reactivation of the parasite can occur in immunocompromised individuals.

Mode of Transmission of Toxoplasma gondii

• Toxoplasma gondii is a protozoan parasite that infects humans by: → Ingestion of contaminated food, water, or soil. → Ingestion of undercooked or raw meat, especially pork, lamb, or venison. → Mother-to-child transmission during pregnancy. → Organ transplantation. → Blood transfusion.

Life Cycle

1. → Cats ingest oocysts from contaminated feces or undercooked meat.
2. → The oocysts excyst in the cat's intestine and release trophozoites.
3. → The trophozoites multiply and form oocysts.
4. → The oocysts are shed in the cat's feces.
5. → Humans can ingest oocysts from contaminated cat feces or undercooked meat.

Memory Trick "Oocysts hatch, Trophozoites invade, Tachyzoites multiply, Cysts form, Reactivation occurs"

Morphology

• The parasite has a distinctive "U" shape under a microscope.
• The trophozoites are 5-6 microns in length and have a pointed end and a rounded end.
• The cysts are 10-14 microns in diameter and have a clear, gelatinous matrix.

Clinical Features

• Asymptomatic infection (70-80% of cases)
• Mild symptoms (fever, headache, fatigue, and muscle aches)
• Severe symptoms (pneumonitis, myocarditis, and encephalitis) in immunocompromised individuals
• Congenital toxoplasmosis (transmitted from mother to fetus during pregnancy)

Complications

• Congenital toxoplasmosis
• Encephalitis
• Pneumonitis
• Myocarditis
• Retinochoroiditis (eye inflammation)

Lab Diagnosis of Human Toxoplasmosis

• Serologic tests: → IgG and IgM antibodies. → Immunofluorescence. → ELISA. → Western blot.

• Parasitologic tests: → PCR (Polymerase Chain Reaction). → Histopathology. → Cyst formation.

Management

• Supportive care (rest, hydration, and pain management)
• Antiparasitic medication (spiramycin or sulfadiazine)
• Preventive measures (avoid undercooked meat, wash hands after handling cat feces, and use gloves when gardening)

Important Points

• Toxoplasmosis is a zoonotic disease, meaning it can be transmitted from animals to humans.
• Pregnant women should avoid contact with contaminated cat feces and undercooked meat.
• Immunocompromised individuals should take preventive measures to avoid infection.
• Toxoplasmosis can be transmitted through organ transplantation or blood transfusion.

Pathogenesis of Toxoplasma gondii

• Attachment: T. gondii cysts attach to the intestinal epithelial cells. → Cysts rupture and release bradyzoites. → Bradyzoites invade host cells. → T. gondii multiplies intracellularly. → Infected cells are carried to the lymph nodes and spleen. → T. gondii disseminates throughout the body. → T. gondii establishes latency in muscle and brain cells.

Clinical Features of Human Toxoplasmosis

• Congenital toxoplasmosis: → Fetal infection during pregnancy. → Microcephaly, hydrocephalus, and intracranial calcifications. → Chorioretinitis. → Hearing and vision impairment. → Developmental delay.

• Acquired toxoplasmosis: → Flu-like symptoms. → Headache. → Fatigue. → Muscle aches. → Swollen lymph nodes.

• Opportunistic toxoplasmosis: → HIV/AIDS patients. → Immunocompromised individuals. → Reactivation of latent infection.

Memory Trick "Tom Cat Eats Mouse, Then You Get Sick"

1. Tom (Toxoplasma) eats (infects) mouse (host) →
2. Mouse (host) gets (infects) Tom (cat) →
3. Cat (Tom) eats (infects) mouse (host) →
4. You (host) get sick (infect) →

This memory trick helps remember the life cycle of Toxoplasma gondii.

Word Trick "TOXOPLASMA" = "Tame Opossums Eat Meat"

This word trick helps remember the name of the parasite.

Remember: "Tom Cat Eats Mouse, Then You Get Sick"