Topic 12: Infectious Diseases Caused by Eukaryotic Microbes: Protozoa & Fungi

Part 1: Protozoan Diseases

Definition: Pathogenic protozoa are often referred to as "parasites".
Examples of Protozoan Diseases: - Malaria - Toxoplasmosis - Cryptosporidiosis - Trichomoniasis

Malaria

Protozoan Agent: Five species of Plasmodium.
Nature of Disease: Malaria is a vector-borne disease.
Vector: Female Anopheles mosquito. - Anopheles mosquitoes not only transmit Plasmodium but are also a required host. - Historically, malaria occurred in both temperate and tropical climates worldwide, including parts of Europe and the US.

Malaria: Significant Global Health Problem

Elimination: Malaria has been eliminated in wealthy countries located in temperate climates.
Continued Threat: Malaria remains a significant threat in tropical areas where mosquito control is challenging.

Life Cycle of Plasmodium

Hosts: Humans and Anopheles Mosquitoes. - (a) Asexual phase: Sporozoite - (b) Exoerythrocytic phase - (c) Erythrocytic phase - (d) Gametocyte phase: Ring trophozoite - (e) Sexual phase: Gametocytes

Malaria in Humans

Systemic Disease: Involves Plasmodium infection of liver cells and red blood cells (RBCs).
Symptoms: - Malaise - Fatigue - Aches - Nausea - Chills - Fever - Sweating
Symptom Pattern: Symptoms rise and fall in 48 or 72-hour cycles depending on Plasmodium species, as infected RBCs rupture synchronously.

Malaria: Potential Consequences

Red blood cell rupture can lead to: - Anemia: A condition characterized by a lower than normal number of RBCs. - Organ Damage: Kidney, liver, and/or spleen damage due to accumulation of debris from ruptured RBCs. - Cerebral Malaria: Worst case scenario where infected RBCs adhere to blood vessels in the brain, reducing blood flow, leading to coma and/or death.

Malaria: Potential Outcomes

Major Recovery: Majority of patients recover fully from malaria.
Chronic Malaria: A small percentage develop chronic malaria, where Plasmodium persists in the liver and causes relapses for several years.
Mortality Risk: A small percentage may die from malaria. The risk of death is highest for: - Fetuses - Newborns - Children - Pregnant females - Other young adults

Malaria: Treatment

Anti-malarial Drugs: Can cure malaria and are often given in multi-drug combinations. - Concern: Plasmodium is becoming increasingly resistant to anti-malarial drugs. - Preferred Approach: Combination therapies are favored to slow the development of drug resistance. - Limited Options: There are only a small number of anti-malarial drugs, raising concern over drug resistance.

Malaria: Prevention

Use of anti-malarial drugs, particularly for travelers.
Methods to reduce mosquito populations and exposure: - Insecticide-treated bed nets - Screens on windows and doors - Repellants - Staying indoors at night (as Anopheles mosquitoes are night feeders).
Vaccine: Recently developed RTS,S vaccine is now recommended by the WHO for children in malaria-endemic areas.

Toxoplasmosis

Protozoan Agent: Toxoplasma gondii.
Prevalence: Widespread in nature; can infect at least 200 species of birds and mammals, including humans.
Zoonotic Disease: The primary reservoir is members of the cat family, including house cats. - Cats become infected by eating prey that is infected. - Infected cats shed T. gondii cysts in feces.

Toxoplasmosis: Cycles of Infection

Modes of infection for humans, mammals (excluding cats), and birds: - Exposure to cat feces, including those in soil. - Ingestion of undercooked meat from infected animals and poultry.

Toxoplasmosis: Disease in Humans

Immunocompetent Individuals: Usually experience no symptoms or mild “flu-like” symptoms. - Most individuals are likely to have been infected at some point and some may carry T. gondii for a long time, kept inactive by the immune system.
Immunocompromised Individuals: T. gondii can cause severe health issues, including: - Development of subacute encephalitis with extensive brain lesions. - Damage to lungs and/or heart, leading to potential death.

Toxoplasmosis: Fetal Infection

If a pregnant woman is infected, T. gondii can cross the placenta and infect the developing fetus: - Infection during the 1st or 2nd trimester can lead to: - Stillbirth - Birth of a newborn with an enlarged spleen and liver - Liver failure - Brain damage and/or blindness.
Transmission Risk: Approximately 33% chance of transmission from mother to fetus.

Toxoplasmosis: Influence on Behavior?

Research suggests that T. gondii may influence brain functions and change the behavior of infected animal hosts, increasing the chances of spreading the parasite.
Potential effects on human brain behavior have been suggested, possibly involved in the development of mental disorders.

Toxoplasmosis: Treatment & Prevention

Treatment: Several anti-protozoan drugs can cure toxoplasmosis but require lengthy treatment.
Prevention: - Pregnant females are advised to avoid all contact with cat feces. - Thorough cooking of meat and poultry. - Regular handwashing after touching cats, used cat litter, sand, or soil.

Cryptosporidiosis

Protozoan Agent: Cryptosporidium coccidi.
Nature: C. coccidi and its cysts are widely found in intestines of mammals, birds, reptiles, and sometimes humans.
Transmission: Occurs through ingestion of food or water contaminated with feces containing the cysts.

Cryptosporidiosis: Disease in Humans

Symptoms: Headache, sweating, vomiting, severe abdominal pain, diarrhea.
Risk: Not life-threatening in healthy individuals; but may lead to chronic infections in AIDS patients, resulting in chronic diarrhea.

Cryptosporidiosis: Outbreaks

Outbreaks can happen when drinking water reservoirs become contaminated with livestock feces after heavy rain, or if human carriers shed cysts into swimming pools.

Cryptosporidiosis: Treatment & Prevention

Treatment: No curative drug exists; however, medications can relieve diarrhea and cramps.
Prevention: - Water disinfection through filtration and UV light, as C. coccidi cysts are highly resistant to chlorine. - Emphasizing personal hygiene. - Advising individuals with diarrhea to avoid public swimming pools.

Trichomoniasis

Protozoan Agent: Trichomonas vaginalis.
Nature: A sexually transmitted infection (STI) that does not form cysts, hence cannot survive long outside a host.
Symptoms: - In females: White to green vaginal discharge, vaginal irritation, or asymptomatic. - In males: Usually asymptomatic.

Trichomoniasis: Potential Complications

For Pregnant Females: Increased risk of premature labor and low birth weight infants, necessitating extensive neonatal care.
Long-Term Issues: Low birth weight can lead to developmental problems, and there is a potential link between trichomoniasis and prostate cancer in males.

Trichomoniasis: Treatment & Prevention

Treatment: Curable with anti-protozoan drug therapy.
Concern: Some strains of T. vaginalis show drug resistance, complicating treatment plans.
Prevention: Standard STI preventive measures, including the use of condoms.

Part 2: Fungal Diseases

Definition: Fungal infectious diseases are referred to as "mycoses".
Examples of Mycoses: - Ringworm - Candidiasis

Ringworm (aka Tinea)

Fungal Agents: Dermatophytes such as Trichophyton, Microsporum, and Epidermophyton.
Nature: A group of cutaneous mycoses affecting hair, skin, and nails.
Symptoms Vary With Location: Common symptoms include itchy skin, red rings or patches, hair loss, and thick, discolored nails.

Dermatophytes

Characteristics: Can tolerate low moisture and salty conditions of the skin surface; do not require living cells as hosts, meaning they can colonize non-living surfaces such as skin and hair.
Nutritional Strategy: They digest keratin found in the skin, hair, and nails but do not invade beyond the surface.

Ringworm: Transmission of Dermatophytes

Common Routes: - Direct contact with infected skin surfaces, hair, or skin cells shed from infected individuals. - Contact with fomites (bedding, clothing, mats, tiles) contaminated with infected cells.
Less Common Routes: - Contact with infected animals. - Contact with soil containing dermatophytes.

Examples of Ringworm

Types: - Tinea capitis: Ringworm of the scalp. - Tinea corporis: Ringworm of the body. - Tinea pedis: Athlete's foot. - Tinea unguium: Ringworm of the nail.

Ringworm: Treatment and Prevention

Treatment: Usually treatable with anti-fungal drugs, with topical applications often sufficient; severe cases may require oral medication.
Prevention: Difficult due to constant shedding of hair and skin cells; avoid contact with dermatophytes when possible.

Candidiasis

Fungal Agent: Candida albicans.
Normal Presence: A member of the normal microbiota in the oral, gastrointestinal, and vaginal regions of most people.
Transmission: Can be spread via direct contact to those who do not already carry it.
Nature: Candidiasis is an opportunistic mycosis resulting from overgrowth of C. albicans due to: - Disruption of normal microbiota (often caused by antibiotic therapy). - Compromised immune systems, diabetes, hormonal changes (e.g., pregnancy, menstrual cycles).

Types of Candidiasis

Vulvovaginal Candidiasis (Yeast Infection): - Symptoms: Thick, white vaginal discharge, inflammation, and itching. - Common during antibiotics, pregnancy, specific menstrual cycles, and in diabetics.
Oral Candidiasis (Thrush): - Symptoms: White lesions and painful inflammation in the mouth and tongue. - Common in infants and immunocompromised individuals.
Candidiasis of the Skin: - Symptoms: Painful, rash-like inflammation of the skin, often mistaken for diaper rash in infants.

Candidiasis: Treatment & Prevention

Treatment: Topical and oral anti-fungal drugs can cure candidiasis.
Prevention: Logical prevention strategies are limited, as C. albicans is a common member of the normal microbiota with many unavoidable reasons that can lead to its opportunistic behavior.