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22 – Pathogenic Fungi
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 Mass exposure to an environmental source of fungi
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Explain why the actual prevalence of fungal infections is unknown
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 No public health agencies nor CDC are notified
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Compare and contrast true fungal pathogens with opportunistic fungi
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 Opportunistic fungi can only infect weakened individuals
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Identify factors that predispose people to opportunistic fungal infections
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Describe the three primary clinical manifestations of mycoses
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 Toxicoses, or poisonings, occur when pathogens are acquired through
ingestion
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 Fungistatic medications (azole drugs) inhibit rather than kill fungi
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Describe Histoplasmosis (causative agent, endemic regions, mode of transmission, clinical manifestations, diagnosis)
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 Spores are inhaled when soil containing the fungus is disturbed by wind
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 Diagnosis is based on the identification of the distinctive budding yeast in KOH- or GMS-prepared samples
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Describe the clinical signs, symptoms and predisposing factors for the following types of localized Candida albicans:

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 It requires traumatic exposure of fungi through the dead outer
layers of skin into the deeper living tissue
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Compare and contrast mycotoxicosis, mycetismus, and fungal allergies
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Myotoxins are most commonly
consumed in grains or vegetables contaminated with fungi
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Mycetismus occurs when untrained individuals
pick and eat wild mushrooms and can result in neurological dysfunction, organ damage, or even death
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It doesn’t require the consumption of myotoxins or fungus
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Explain the difference between a definitive and an intermediate host
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 The intermediate host is the host that includes an asexual reproduction stage of the parasite
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What are the major routes by which humans acquire parasitic infections?
 By being ingested, via vector transmission, or via direct contact and penetration of skin
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Among the protozoa that enter the body through ingestion, most have two morphological forms
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 A feeding and reproducing stage called a trophozoite, which lives within the host
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 A cyst can undergo excystment and develop into new trophozoites
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Describe the epidemiology of Entamoeba histolytica: transmission, reservoirs, disease types, and diagnosis
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 Disease are 3 types of amebiasis: (from least severe to most)
o Luminal amebiasis: Trophozoites remain in the lumen of the intestine
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o Invasive extraintestinal amebiasis: Trophozoites invade the peritoneal cavity and the blood
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o Affects the eye and brain
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 Naegleria: Can have a flagella
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o Amebic meningoencephalitis disease can lead to neurological tissue destruction, coma, and death
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Explain Trypanosoma brucei and Trypanosoma cruzi with geographic distribution, vector, mechanism of
transmission, target organ, and disease
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 Disease - African trypanosomiasis (African sleeping sickness)
Trypanosoma cruzi
 Geographic distribution - Central and southern America
 Vector - Triatomine bugs (kissing bug)
 Mechanism of transmission - Through the feaces of insect vectors
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 It’s a zoonosis, a disease of animals transmitted to humans
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 Mucocutaneous leishmaniasis is when skin lesions enlarge to encompass the mucous membranes of the mouth
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Macrophages spread parasite to the liver, spleen, and lymph nodes
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Describe the biology of Giardia intestinalis in terms of its zoonotic and environmental reservoirs, mode of
transmission, and disease
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Beavers are common zoonotic sources
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Likewise, contact with feces during sex can spread infection
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 Fever correlates with erythrocyte lysis and results from efforts of the immune system to remove cellular debris,
toxins, and merozoites
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 The inability of the liver to process the hemoglobin released from dying erythrocytes results in jaundice
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What is the common way to diagnose malaria? What are some of the more common methods of malaria control?
 Microscopy is used for diagnosing because Plasmodium can be readily distinguished in blood smears
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Widespread use of insecticides,
drainage of wetlands, and removal of standing water can reduce mosquito breeding rates
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 Humans become infected by ingesting undercooked meat containing the parasite
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What are the groups and organ arrangement?
 Adult worms are either dioecious, meaning that the male and female sex organs are in separate worms, or
monoecious, meaning that each worm has both sex organs
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Know the components of the generalized anatomy of a tapeworm
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Describe the common features of the life cycles of tapeworms that infect humans
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Then, intermediate hosts (like pig) ingest the eggs on contaminated food
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In the muscle, larva develops
into a cysticercus
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The cysticercus excysts in the human’s intestine
and becomes a scolex that attaches to the mucosa of the small intestine
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solium? Regarding humans, what is one key
difference between these two species?
 Taenia saginata: Beef is an intermediate hosts and human is definitive
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 Rarely, humans could be intermediate hosts in T
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Never in T
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 Ascaris lumbricoides
o Adults reproduce in the small intestine, where females produce about 200,000 eggs every day
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The parasites subsequently develop into adults in the intestine
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 Hookworm (2 types: Ancylostoma duodenale and Necator americanus)
o Eggs passed in the stools of infected humans are deposited in soil, where they hatch
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The larvae
burrow through human skin and are carried by the circulatory system to the heart and the lungs
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The disease is hookworm disease
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Scratching dislodges eggs onto clothes or bedding, where they dry out, become airborne, and
settle in water or on food that is then ingested
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 Filarial nematode is a type of nematode that infects lymphatic system of vertebrate hosts
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The microfilariae
develop as a mosquito and migrate to the salivary glands
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 In contrast, intestinal nematodes release their eggs into the intestine, where they enter the
environment through the feces
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24 – Pathogenic DNA Viruses
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 Smallpox is characterized by malaise, delirium, and prostration, followed by lesions on the skin
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The papules often occur in lines where the virus has been spread by scratching
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Describe the progression of disease in poxvirus infections
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Then, the macules turn into raised sores
known as papules
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They eventually dry up to form a crust and leave scars
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What was Edward Jenner’s contribution?
 Edward Jenner used cowpox virus to successfully protect against smallpox due to the similarity of both antigens
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What are the virulence factors of smallpox virus?

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Remains stable in aerosol form; highly contagious between people; can remain viable for as long as 24 hours
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What factors made it possible for smallpox to be successfully eliminated?
 An inexpensive, stable, and effective vaccine (cowpox virus) was available
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 The severe, obvious signs and symptoms of smallpox enable quick and accurate diagnosis and quarantine
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 The virus is spread only via close contact
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Describe latency as it occurs in herpesviruses
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 They may reactivate as a result of aging, chemotherapy, immunosuppression, or physical and emotional stress
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 Oral herpes is caused by human herpesvirus 1
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Can be controlled with chemotherapeutic agents
such as valaciclovir
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Infection by HHV-2 results in painful lesions on
the genitalia and occasionally oral lesions
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The only true prevention is sexual abstinence or faithfulness between uninfected partners
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Can be controlled with uridine or trifluridine
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Health care workers should always wear
latex gloves when they are treating a patient with herpes simplex
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Prevention includes delivery of the baby by cesarean section if
genital lesions are present
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 Chickenpox occurs when the virus enters the body through the respiratory tract or eyes, replicates, and travels
throughout the body via blood
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 Shingles occurs when the dormant virus is reactivated due to stress, aging, or immune suppression
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Unlike chickenpox, the rash occurs only in the proximity associated with an infected nerve
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Know that HH-4 (a
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a
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 Seed warts are found on the fingers or toes; plantar warts are found in the soles of the feet; flat warts are
found on the face, trunk, knees, or elbows; genital warts are found on the external genitalia
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Describe the epidemiology, pathogenesis, diagnosis, treatment, and prevention of genital warts
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 Spreads via direct contact, sex, fomites, and differing locations on a person by a process called autoinoculation
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 Prevention includes abstinence, mutual monogamy, and Gardasil (a vaccine)
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Hepatitis B viruses replicate in liver cells and are released by exocytosis rather than cell lysis
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 Transmitted when infected body fluids enter the skin or mucous membranes
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 Hepatitis B does not have a single effective treatment
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End-stage chronic hepatitis B may require a liver transplant
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Also, sharp instruments should always be properly sterilized
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Describe the evidence that HBV causes hepatic cancer
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Further, hepatic cancer cells contain the hepatitis B virus genome and to express the HBV
antigen
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25 – Pathogenic RNA Viruses
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RNA viruses of humans are categorized into families based on what three features?
 Genome structure, presence of envelope, and size/shape of their capsid
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Discuss the epidemiology and treatment of the common cold
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 Can be transmitted via coughing, sneezing, and fomites
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 Polioviruses may cause asymptomatic infections
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 …may cause nonparalytic polio, in which it invades the central nervous system and meninges
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o Varying degree of paralysis occur
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 Jonas Salk developed an inactivated polio vaccine in 1955, and in 1961, Albert Sabin developed a live,
attenuated oral polio vaccine
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 Noroviruses cause diarrhea, nausea, and vomiting and were first discovered in the stools of victims
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Define arbovirus
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 West Nile virus spread from NYC throughout United States by infected migratory birds, which further
spread to mosquitoes, to horses, and eventually humans
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 The first phase is a week of high fever, edema of the extremities, weakness, and severe pain
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Reinfection results in dengue hemorrhagic fever, which is more serious
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 Degeneration of the liver, kidneys, heart, and massive hemorrhaging
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Liver damage presents as jaundice
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Explain how retroviruses don’t conform to the central dogma of molecular biology
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 An RNA-DNA hybrid is made from the +RNA genome using tRNA carried by the virus
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 The RNA of the hybrid molecule is degraded by reverse transcriptase, and transcribes a complementary +ssDNA
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 AIDS is not a single disease but a syndrome, that is, a complex of signs, symptoms, and diseases associated with
a common cause
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Describe the process by which HIV attaches to and enters a host cell; be sure to include the roles of gp41 and gp120
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Describe the key steps in the replication cycle of HIV
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HIV primarily attaches to helper T cells; cells of the macrophage
lineage, smooth muscle cells, and dendritic cells
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HIV triggers the cell to endocytose
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The viral envelope fuses with the vesicle’s membrane
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Reverse transcriptase used to make dsDNA from ssRNA
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The dsDNA enters the nucleus and becomes part of a human DNA
 Synthesis of viral RNA and polypeptides
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No active enzymes or capsid yet
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o Assembly and maturation
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HIV is now mature
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Where did HIV likely come from, i
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what is its origin?
 HIV may arose from mutation of a similar virus, simian immunodeficiency virus (SIV), found in African monkeys
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Describe the role of helper T cells in HIV replication and the clinical course of AIDS
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(1): Fever, fatigue, weight loss, diarrhea, and body aches accompany primary infection
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(3): The body and HIV are waging an invisible war with few signs or symptoms
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(4): Integrated viruses continue to replicate to an extent that the body cannot make enough helper T cells (green line)
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 All body secretions of AIDS patients contain HIV
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 Transmission usually occurs via any type of sexual contact or intravenous drug use
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Describe some of the problems that must be overcome in developing an effective vaccine against HIV
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 IgG, a necessary component of a vaccine, can form IgG-viral complexes which bind to B cells
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 HIV mutates often, generating antigenic variants that enable it to evade the immune response
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 HIV infects and inactivates macrophages, dendritic cells, and helper T cells—cells that combat infections
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 Coughing, sneezing, and talking spread measles virus in the air via respiratory droplets
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 Signs and symptoms include fever, sore throat, headache, dry cough, and conjunctivitis
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What are its reservoirs and how is it transmitted?
 Rabies a virus that invades the central nervous system, causing seizures, hallucinations, disorientation,
hydrophobia, and paralysis
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 The rabies vaccine, or human diploid cell vaccine, is effective in preventing rabies
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Then, human rabies immune globulin is
injected, and five vaccine injections are administered
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o Transmission includes breaks in skin such as biting
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What is the natural reservoir for filoviruses? How are they transmitted between humans?
 The natural reservoirs of filoviruses appear to be fruit bats
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 The virions attack many cells of the body, especially macrophages and liver cells
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 Hemagglutinin and neuraminindase make up the prominent glycoprotein spikes on the influenza virion’s
envelope
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Neuraminindase spikes hydrolyze mucus in the lungs, thereby providing the virus access to cell surfaces
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Compare and contrast antigenic drift and antigenic shift
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o This process is much influenced by presence of antibodies produced against predecessor strains
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 The antigenic shift is observed in major changes in hemagglutinin or neuraminidase or both
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