Microorganisms & Viruses

Dermatophytes

• A closely-related group of fungi 

• Symptoms: cutaneous fungi infections ⇒ “ringworm” 

  • Ringworm can present anywhere on body: scalp, feet, hands, nails, groin

• Transmission: 

  • Contact with person/animal with dermatophyte infection 

  • From the environment (surfaces of damp areas)

Histoplasma capsulatum

• Pathogenesis: inhaling fungal spores 

• Transmission: grows in soil with high nitrogen content → bird & bat poop 

• Most cases are asymptomatic 

  • Few cases (5%): acute pneumonia develops and less often followed by progressive disseminated disease 

  • This level of disease occurs in debilitated and/or immunosuppressed individuals 

• Causes histoplasmosis 

Cryptococcus neoformans

• Pathogenesis: inhaling the fungus 

• Transmission: fungus found in soil, on decaying wood, and bird (pigeon) droppings 

• Symptoms: pneumonia-like illness 

  • Fungal meningitis → high tendency for systemic spread to the brain and meninges 

• Infections are rare for healthy people 

  • But detrimental for HIV/AIDS patients 

• Causes cryptococcosis

Candida species 

• Yeast 

• Opportunistic pathogen 

  • Within the human: growth is limited by competition and immune system 

  • Disease results from overgrowth 

• Symptoms: 

  • “thrush”/oropharyngeal candidiasis = candidiasis that develops in mouth/throat 

    • White patches or plaques on tongue and oral mucous 

  • “Yeast infection” = candidiasis that develops on the genitals 

    • Happens when there is overgrowth of the normal fungal microbiota 

  • Women → vulvovaginal candidiasis 

  • Men → genital candidiasis → itchy external rash 

• Causes candidiasis 

Acanthamoeba species

• Causes keratitis (inflammation of the cornea) 

• Transmission: found in freshwater, tap water, hot tubs, and soil 

• Pathogenesis: contaminated contact lenses 

  • Infection begins with mild inflammation → severe pain 

Trypanosoma brucei

• Causes African trypanosomiasis / “African sleeping sickness” 

• Transmission: tsetse fly 

• Symptoms: infects & deteriorates the CNS 

Trypanosoma cruzi

• Causes American trypanosomiasis / Chagas disease 

• Tranmission: reduviid bug / “kissing bug”

• 20-30% of people develop the chronic form of the disease 

  • Symptoms: damages the nerves and heart 

Toxoplasma gondii

• Causes toxoplasmosis 

• Tranmission: cats

  • When food or water is contaminated with feces containing the protozoa 

• The primary danger is cogenital infection (an infection that is present in a baby at the time of birth) 

Plasmodium falciparum

• Causes malaria 

• Transmission: Anopheles mosquito 

  • Mosquito bite introduces the protozoa into the host’s bloodstream → infects and lyses RBC 

• Symptoms:

  • Anemia 

  • Lysed RBC blocks blood vessels → tissue death 

Giardia lamblia

• Causes giardiasis → a prolonged diarrheal disease 

• Transmission: drinking untreated contaminated water 

Taenia species

• Tapeworms are composed of a head and successive segments 

  • Each segment is full of eggs that pass thourgh the anus of the host to be consumed by the a host 

• Transmission: uncooked meat containing the larvae is ingested 

• A tapeworm may grow for many years in the digestive tract of the host without notice 

• May migrate to muscle, brain, or liver and form cysts ⇒ pain and neurological symptoms (seizures) 

Herpes simples viruses (HSV-1 & HSV-2)

• -1 = infections above the waist (oral infections)

• -2 = genital infection 

• Transmission: direct contact with active lesion or body fluids containing the virus 

  • travels through small breaks in the skin or mucous membrane 

• Symptoms: 

  • Blisters on the lips, fingers, skin, genital 

  • Herpes encephalitis or meningitis = ___ infection of the brain/meninges 

  • Neonatal herpes = virus crosses the placental barrier and infects the fetus 

    • Spontaneous abortion or fetal damage 

• is never removed from the body by the immune system 

• Following a primary infection, the virus migrates to a nerve ganglion and remains as a latent virus → asymptomatic 

Varicella zoster virus

• Transmission: inhaled and initially multiplies within the lungs 

  • Then circulates through the blood and localizes to the skin 

• Symptoms:

  • Chickenpox = a rash and the formation of skin vesicles 

  • Remains latent but could reactivate as shingles 

    • Vesicles are distributed along affected cutaneous sensory nerves 

Human papillomarvirus (HPV)

• Transmission: person to pearson through contact 

• Symptoms: warts or cancerous lesions 

  • Warts on skin or mucosa 

  • Anogenital and oropharyngeal cancers 

Rubeola virus

• Transmission: airborne through coughing and sneezing 

  • After replicating in the lungs → spreads throughout the body through the bloodstream 

• Symptoms: 

  • Measles → fever, runny nose, cough, red eyes, and sore throat 

  • Koplik’s spots appear during initial symptoms 

  • A rash develops 2-3 days later → spread over the body 

Influenza virus

• Transmission: airborne droplets or contact with contaminated objects 

• Symptoms: Influenza (the flu) 

  • Chills, headache, dry cough, fever, malaise, muscle aches, and inflammation of the soft palate 

Rhinovirus & Coronavirus

• Transmission: airborne droplets 

• Symptoms: the common cold 

  • Sneezing, nasal secretion, congestion, sinusitis, laryngitis, earache

• Medication can relieve symptoms but viral infection must run its course 

Rotavirus

• Transmission: fecal-oral route 

• Symptoms: gastroenteritis 

  • Vomiting, diarrhea, fever, and abdominal pain 

Poliovirus

• Transmission: fecal-oral route by ingesting food or water contaminated with feces containing the virus 

• Symtoms: poliomyelitis (polio) 

• Only a low number (10%) of those who become infected show any symptoms 

  • Initial symptoms: sore throat, fever, nausea 

• In fewer cases, the virus moves to the blood after ingestion → viremia 

  • If the viremia is persistent → virus can enter the CNS

  • Meningitis develops 

  • Destruction of motor neuron in the spinal cord leads to paralysis 

• For the 1% where CNS is affected → death can result from respiratory failure 

Rabies virus

• Transmission: the bite of an infected animal 

  • The virus multiplies in the PNS and moves to the CNS 

• Symptoms: rabies 

  • Irritability, muscle spasms, difficulty swallowing (after virus reaches CNS)

  • animals are restless then highly excitable, biting at anything within raech

  • Without early treatment → fatal encephalitis 

Ebola virus

• Transmission: direct contact with blood or other body fluids of an infected person 

• Symptoms: hemorrhagic fever, unexplained hemorrhaging 

Heptatitis virus

• inflammation of the liver 

• Symptoms:

  • Nausea and vomiting 

  • Abdominal pain 

  • Dark urine 

  • Light-colored stools 

  • Jaundice 

• A & E are transmitted through fecal-oral route 

  • Contaminated food or water

  • Close contact with someone who is infected 

• B, C, & D are transmitted through 

  • Blood transfusions

  • Contaminated dental/medical instruments

  • Needles 

  • Sex with an infected parter

  • Birth from an infected mother

Human immunodeficiency virus (HIV)

• Symptoms: acquired immunodeficiency syndrome 

  • Immunodeficiency results from the loss of helper T cells 

• Transmission: 

  • Blood transfusions, needles, etc

  • Sex with an infected parter 

  • Birth from an infected mother 

  • Mucosal contact with infected blood or body fluids 

  • Once the virus gets into the body → infect helper T cells 

• HIV = retrovirus 

  • Retrovirus = a virus that has an RNA genome → upon infection of a host cell → retroviral RNA converted to DNA 

• The viral DNA is then inserted into the host cell’s DNA ← provirus 

• Process of infection:

  • Upon entry into the helper T cells → viral RNA genome is converted into double-stranded DNA using its own reverse transcriptase enzyme 

  • The viral DNA is then imported into the cell nucleus and is integrated into the cellular DNA by integrase 

  • Once integrated → provirus may become latent 

  • Alternatively: provirus may be transcribed → producing new RNA genomes, viral proteins, and ultimately infectious virions 

• Symptoms of early-stage HIV infection:

  • Some people may experience flu-like illness within 2-4 weeks after HIV infection, but some people may not feel sick during this stage 

  • During this time, HIV infection may not show up on an HIV test → but is still highly-infectious 

• Symptoms of clinical latency: 

  • Clinical latency stage = chronic HIV infection 

  • During this stage, HIV is still active but reproduces at very low levels 

  • People with chronic HIV infection may not have any HIV-related symptoms or only mild ones 

• Symptoms of AIDS: 

  • Many of the severe symptoms and illnesses of AIDS come from opportunistic infections that occur because the body’s immune system has been weakened