Eukaryotes: Fungi, Algae,
Protozoa, and Helminths
Characteristics of Fungi
• Macroscopic Fungi (mushrooms)
• Microscopic Fungi (molds and yeasts)
– Dimorphic: can be either hyphae or yeast
– Hyphae: long, threadlike cells
– Mycelium: hyphae grow to form filamentous
mass visible to unaided eye (The fuzzy mold
you see growing on old food).
– Filamentous fungi can reproduce sexually and
asexually by the formation of spores
• Spores can either be sexual or asexual
• Asexual spores are formed from hyphae.
– They are an exact copy of the parent, no genetic
variation.
• Sexual spores are formed by fusion of 2
opposite mating strains of the same species
of fungus.
• Spores are important in the identification of
pathogenic strains of fungi because they
have their own individual structures that can
be identified microscopically.
Fungal Diseases
• Any fungal infection is called a mycosis.
• Mycoses (plural form of mycosis) are grouped
into 5 categories:
– 1. Systemic: deep w/in body affecting multiple organs
or tissues
• Route of transmission is inhalation of spores.
• Ex. Coccidioidomycosis: a form of pneumonia that is most
commonly found in AIDS patients. It generally can be found
in the lungs of a healthy individual without causing infection.
Pneumonia caused by this organism became a widely
recognized symptom of AIDS infection.
– 2. Subcutaneous: beneath the skin
• Route of transmission is direct implantation of
spores into puncture wound in the skin.
• http://dermnetnz.org/fungal/fungi-general.html
– See the above website for a description and pictures of an
example of a subcutaneous infection.
– 3. Cutaneous: epidermis, hair and nails
• Route of transmission is human to human, animal to
human, or direct contact with infected hair and
epidermal cells.
• Examples of cutaneous mycosis: Ringworm
– Ringworm is often thought to be caused by a worm simply
because of it’s name. It’s true classification is that of a
fungal infection.
– Tinea Capitis: infection of the scalp
– Tinea Barbae: infection of the beard
– Tinea Corporis: infection of the body
– Tinea Cruris: infection of the groin
– Tinea Pedis: infection of the feet
– Tinea Manuum: infection of the hands
– Tinea Unguium: infection of the nails
– Symptoms: http://dermnetnz.org/fungal/tinea.html
» See the above web address for great pictures and
descriptions of symptoms for each infection.
• General Transmission: direct or indirect contact
with other infected humans or animals.
• Diagnosis: A piece of skin, hair or nail will be sent
to a lab to grow the fungus in a test tube
• Prevention and Rx: avoid contact, keep
susceptible skin areas dry
– Try to remove shoes when possible to dry out feet.
– Avoid touching places such as locker room floors or
other public places with bare feet.
– Never borrow other people’s shoes.
– Have pets checked if areas of hair loss are seen.
– Topical antifungal agents are the first choice of treatment
in mild infections. In moderate to severe cases an oral
antifungal is prescribed.
– http://familydoctor.org (This is where I found my info on
diagnosis and prevention.)
– 4. Superficial: Localized along hair shafts and
surface epidermal cells
• Prevalent in tropical climates
– 5. Opportunistic:
• Pneumocystis: An additional type of fungal
pneumonia found primarily in HIV infected patients.
• Stachybotrys: mold growing on water-damaged
walls of homes. This is the mold responsible for
making home owner’s insurance rates sky rocket in
Texas.
– Can cause fatal pulmonary hemorrhage in infants when
spores are inhaled
– See the following web address for transmission,
symptoms, and safe handling procedures.
http://www.idph.state.il.us/envhealth/factsheets/stachybotr
ys.htm
• Yeast infections by Candida albicans:
– Thrush: common infection of the mouth in infants and
toddlers or other immuno-compromised individuals.
– Symptoms:
» Ulcer/skin lesion in the mouth (usually on the tongue
or inner cheeks)
» Painful
» Slightly raised area
» Creamy white appearance
» May appear curd-like ("cottage cheese" appearance)
» Dry mouth
– Diagnosis: physical examination by a physician
– Treatment: oral antifungal medication
• Antifungals:
– Block replication and speed up skin loss
– Some mimick structures found in the fungal
cells preventing cell division or replication.
Algae
• Algae are very useful but also cause some
food poisoning
• The agar used in media is extracted from
red algae.
• Thickeners called carageenen, used in ice
cream and evaporated milk, are derived
from red algae called Irish Moss.
• Dinoflagellates (unicellular algae called
plankton)
– Dinoflagellates belonging to genus
Alexandrium produce neurotoxins that cause
paralytic shellfish poisoning.
– Mollusks and clams eat algae and the
neurotoxin is concentrated inside. When
humans eat mollusks and clams that have eaten
this type of algae they can become sick.
– Current recommendations to avoid sickness are
to avoid harvesting mollusks and clams during
a red tide. A ride tide is caused by a large
concentration of dinoflagellates in the water.
Protozoa
• Protozoa are unicellular eukaryotic
organisms that inhabit water and soil.
• The feeding and growing stage is called the
trophozoite.
• Under adverse conditions some protozoa
produce a protective capsule called a cyst.
Medically Important Phyla of
Protozoa
• Archaezoa:
– Trichomonas vaginalis: found in vagina and male
urinary tract.
• Signs and Symptoms:
– Asymptomatic in 50% of infections
– Females, White to Green discharge, chronic infection may lead
to infertility.
• Transmission: sexual intercourse with infected partner.
• Prevention and Rx: no vaccine, metronidazole.
– Metronidazole interferes with anaerobic metabolism.
– Giardia lamblia: found in small intestines of
humans and other mammals
• Signs and Symptoms:
– Diarrhea of long duration, abdominal pain and flatulence
– Stools greasy, malodorous quality to them
• Transmission: Excreted in feces and survives in
environment until ingested by host. For example, an
infected animal wanders down to a beautiful
mountain stream to take a drink and defecates while
there. An unsuspecting hiker sees the beautiful
mountain stream and decides to have a drink
because it can’t possibly be dirty, it is too
beautiful….
• Prevention and Rx: vaccine for animals, avoid
drinking from freshwater sources.
– Quinacrine or metronidazole
Medically Important Amoeba
• Rhizopoda: (aka amoeba)
– Apicomplexan: obligate intracellular parasites,
in other words, they can only live inside host
cells.
• Plasmodium: causative agent of malaria
– Transmitted through bite of anopheles mosquito
– Life Cycle of malaria see Fig. 20.15 in your textbook.
– Transmission: spread by the bite of an infected female
Anopheles mosquito and sometimes through shared
needles, blood transfusions and from mother to fetus.
– Signs and Symptoms: 10-16 day incubation period.
» Malaise, fatigue, vague aches and nausea with or
without diarrhea, followed by bouts of chills, fever
and sweating.
– Diagnosis: examination of blood smears microscopically
as well as history of travel in endemic areas.
– Treatment: Quinine, chloroquine. There mode of action is
unknown. Long term therapy using primaquine or
proguanil can eventually eliminate the parasite from the
liver.
– Prevention: long term mosquito control by getting rid of
standing water used for breeding, spraying insecticides.
» Humans can prevent infection by using netting,
screens, repellants to keep mosquitoes out and
remaining indoors at night.
– Prophylatic drugs can also be taken as a preventative measure
but are usually too expensive for people in developing countries
• Malaria is an important and deadly disease.
• 300 million to 500 million new cases are reported
each year (how many unreported?).
• 90% of the new cases are reported in Africa where
the people cannot afford drugs for prevention.
• Almost 2 million children and young adults die
from this disease each year.
• 1,000 to 2,000 new cases a year are seen in the
United States.
• Other examples
– Toxoplasma gondii: Can cause infections in
utero when women clean feline litter boxes
while pregnant.
• Approximately 50% of cats are infected with this
organism.
• Through the course of the infection the cat will
begin to shed oocysts (infective form of pathogen
shed in the feces).
• Oocysts are very resistant to adverse environmental
conditions and can remain infective for months.
• Humans can also be infected via raw meat that is
infected with the organism.
• Signs and symptoms: most cases are
asymptomatic or marked by mild symptoms such
as sore throat, swollen lymph nodes, low grade
fever.
– It is known to be transmitted tranplacentally. There is a
33% chance of transmission from mother to fetus,
ultimately causing stillbirth, liver failure,
hydrocephalus, convulsions, damage to retina.
• Diagnosis: check serum for antibodies.
• Treatment: pyrimathamine, sulfadiazine or both in
combination.
• Prevention: Adequate cooking of meat, washing
hands after handling cats or cat feces.
Helminths
• 2 types:
– 1. Platyhelminths: flatworms
– 2. Nematoda: roundworms
Platyhelminths
• Divided into 2 classes:
– 1. Trematodes (aka lung, liver, blood flukes)
• Have flat, leaf shaped bodies
• Have ventral suckers and oral suckers for
attachement.
• Ex. Schistosomiasis
– Approximately 250 million people infected.
– Adult worms are 10-20mm long.
– Transmission: skin penetration by organism in fresh
water.
– Symptoms: penetration of organism causes itching as
known as swimmer’s itch.
» Spenomegaly, blockage of the bladder
» In severe cases may cause life threatening dysentery.
– Diagnosis: Microscopic examination of eggs.
– Treatment: Praziquantel is the drug of choice.
– 2. Cestodes (tapeworms, intestinal parasites)
• The head (or scolex) has suckers for attachment,
some species also have small hooks for attachment
• Body made up of segments called proglotids that
contain both male and female reproductive organs.
• Mature proglotids are basically sacs of eggs.
• Ex. Taenia saginata: beef tapeworm, live in
humans, transmission through consumption of
undercooked meat. Adult worms can be up to 4-6
meters long.
• Ex. Taenia solium: pork tapeworm, transmission
through consumption of undercooked meat. Adult
worms are slightly smaller than the beef tape worm.
• Symptoms: light infection are asymptomatic
– Heavier infections may produce abdominal discomfort,
vomiting, and diarrhea.
– Contrary to popular belief, tape worms do not usually
contribute to significant weight loss.
– Complications can arise when heavy infections cause
intestinal blockage.
• Diagnosis: recovery of eggs from stool or perianal
area.
• Treatment: Praziquantel
– Some drugs used to treat helminth infections paralyze the
infecting organism.
– Niclosamides inhibit ATP production.
Nematodes
• Also known as roundworms.
• Cylindrical and tapered at each end (like an
earthworm).
• Most species have a male and female,
generally males are smaller than females.
• Classified according to whether the egg or
the larva is infective in humans.
Eggs infective for humans
• Enterobius vermicularis: pinworms
• Adult pinworms found in intestine, female migrates to anus to
deposit eggs at night. A single female can produce more than
10,000 eggs.
• Transmitted by ingestion of eggs through contaminated
clothing, bedding, carpet, etc. The infected person’s hands will
also be contaminated with the eggs and provide a route for
reinfection of the infected individual and dispersal of eggs to
new victims.
• When an individual is diagnosed with pinworms the whole
family is generally treated.
• Signs and symptoms: perianal itching
• Diagnosis: Graham sticky-tape method
– Transparent tape is placed on perianal skin the sticky side
picks up eggs, then examined microscopically
– Parents usually have to do this since the eggs are deposited
in the early morning hours.
• Treatment: mebendazole
Larvae Infective for Humans
• Necator americanus: hookworm, live in small
intestine
–
–
–
–
Eggs excreted in feces
Larvae hatch in soil and enters host through skin
Moves to lungs through blood and lymph vessel
Coughed up on sputum, swallowed and carried to small
intestine
– Diagnosis based on presence of eggs in feces
– Avoid hookworm infections by wearing shoes
• Adult worms live in the lumen of the small
intestine, where they attach to the intestinal
wall with resultant blood loss by the host.
• Most adult worms are eliminated in 1 to 2
years, but longevity records can reach
several years.
• The most significant complication due to a
hookworm infection is the anemia due to
the large amount of blood lost to the worm
• Trichinella spiralis: referred to as trichinosis
– Acquired by eating larvae in poorly cooked pork
– Larvae mature into adults in small intestine and
sexually reproduce
– Eggs develop in female and she gives birth to live
nematodes
– Larvae enter blood and lymph vessels and migrate
throughout body
– Encyst in muscles and other tissue and remain there
until ingested by another host
– Diagnosis is made microscopically –muscle biopsy
examined for larvae
• See pae 362-363 in your textbook for a good
summary of drugs used to treat eukaryotic
infections.
• The most important thing to understand when
treating eukaryotic infections is that their cellular
structure is very similar to our own body’s cellular
structure. Finding targets that are different enough
to not cause harm to our body is very difficult. As
a result many drugs can cause harmful sideeffects.
Bibliography
• www.medline.com
• www.med.sc.edu:85/parasitiology.htm
• www.biosci.ohio-state.edu/~parasite.html