Common Parasitic Infections Overview

Common Parasitic Infections

•  The lecture covers common parasitic infections, including amoebiasis, giardiasis, and toxoplasmosis.
•  The College of Medicine, King Faisal University, is the source of the presentation.

Differences between Diarrhea and Dysentery

•  Dysentery involves painful evacuations of small amounts of stool containing blood and mucus.
•  Diarrhea is characterized by increased frequency, fluidity, or volume of bowel motions.
•  Entamoeba histolytica and Balantidium coli are common parasites causing dysentery.
•  Giardia lamblia, Cryptosporidium, and Cyclospora are common parasites causing diarrhea

Pathogenesis of Intestinal and Extraintestinal Amoebiasis

•  Infection can result in a carrier state, intestinal amebiasis, or extraintestinal amebiasis.
•  Ingesting cysts leads to trophozoite release in the duodenum, which eventually cause tissue necrosis in the large intestine.
•  Tissue destruction is caused by a parasite-produced cytotoxin.
•  Amoebic adherence to host cells is facilitated by a galactose-inhibitable protein.
•  The damaging effect of the parasite is linked to cell membrane permeability disruption and the release of toxic neutrophil components.

Amoebiasis [Invasion]

•  Parasite invasion can extend to the peritoneal cavity.
•  Organ involvement often includes the liver, lungs, brain, and heart.
•  Amoebiasis can be spread via the bloodstream.

Pathogenesis of Amoebiasis

•  The presentation details the process of amoebiasis (infection by Entamoeba histolytica).
•  The life cycle, from ingestion of cysts to tissue damage, is highlighted.
•  The lecture describes how the parasite enters the body, multiplies, and causes tissue destruction.
•  It also includes the types of ulcers that arise from this infection.
•  The cycle also explains how the organism releases factors, like a cytotoxin, to damage the host.

Clinical Syndromes of Amoebiasis

• Intestinal Amoebiasis: Often presents with abdominal pain, cramping, colitis, and dysentery. Severe cases show bloody stools.
• Extra-Intestinal Amoebiasis: Characterized by fever, leukocytosis, rigors, abscess formation, and liver lobe involvement, particularly the right one. Frequently presents with signs of inflammation and secondary bacterial infection.

Clinical Syndromes of Amoebiasis [Asymptomatic Carrier]

•  80-90% of amoebiasis cases are asymptomatic (cyst passers).
•  Patients might experience general abdominal discomfort, distension, and diarrhea alternating with constipation.

Management of Amoebic Carrier

•  Treatment for asymptomatic carriers generally uses Iodoquinol (luminal, intestinal) for 10 days.
•  Systemic infection is treated with Metronidazole (Flagyl) for 10 days.

Pathogenesis of Giardiasis

•  Giardia duodenalis attaches to the intestinal villi by a sucking disk.
•  The parasite multiplies through binary fission.
•  No significant tissue necrosis is typically observed.

Clinical Syndromes of Giardiasis

•  Approximately 50% of Giardia infections are symptom-free.
•  Symptoms, occurring between 1 and 4 weeks, include dyspepsia, epigastric pain, nausea, flatulence, abdominal cramps, and explosive watery diarrhea with a foul odor.
•  Severe cases can lead to malabsorption of nutrients (steatorrhea).

Clinical Syndromes of Giardiasis [2]

•  Spontaneous recovery often happens within 10 to 14 days, though multiple relapses are possible.
•  IgA deficiency patients may experience more chronic cases.

Toxoplasmosis: Mode of Infection and Transmission

•  Toxoplasma gondii is an intracellular parasite.
•  Humans can contract the infection from eating undercooked meat, food/drinks contaminated with cat excreta, blood transfusions, organ transplantation, and exposure to mucous membranes or skin abrasions.
•  Vertical transmission (from mother to child) during pregnancy can also occur.

Stages of Toxoplasma gondii

• Toxoplasma gondii develops in the intestinal cells of cats, and during an extraintestinal cycle, traveling to tissue via bloodstream.
• The parasite has different forms (tachyzoites, bradyzoites) with differing functions and locations in the body.

Toxoplasmosis in the Immunocompromised

•  Reactivation of latent toxoplasmosis can lead to severe neurologic complications, such as encephalopathy, meningoencephalitis, or cerebral mass lesions.
•  Lesion location impacts the symptoms, commonly including hemiparesis, seizures, visual defects, confusion, and lethargy.

Diagnosis of Toxoplasmosis

•  Serology is often used to detect IgM for acute infection and IgG for ongoing infection.
•  PCR can detect parasite DNA in the urine or amniotic fluid (important for congenital infections).

Treatment and Prevention of Toxoplasmosis

•  Pregnant women are often given spiramycin, alongside pyrimethamine and trisulphapyrimidine.
•  Prevention involves avoiding undercooked meat and exposure to cat feces.

Congenital Toxoplasmosis

•  Infections during pregnancy can cause complications in the developing fetus, potentially leading to abortion, stillbirth, or severe neonatal manifestations (including epilepsy, encephalitis, and microcephaly).
•  Late issues include blindness from chorioretinitis, mental retardation, and other neurologic disorders.

Acquired Toxoplasmosis

•  Acquired toxoplasmosis typically causes an asymptomatic infection characterized by tissue cysts.
•  In symptomatic cases, acute presentation includes lymphadenitis, chills, fever, headache, myalgia, skin rash, and splenomegaly.
•  Chronic cases show additional symptoms such as hepatitis, encephalomyelitis, and myocarditis, sometimes culminating in blindness from chorioretinitis.

References

•  Medical Microbiology, 8th edition (Murray, et al.) Chapters 73 & 74.
• Other images are from Google.