infect

dogs, cats, and monkeys and

Filarial nematodes are

transmitted through

the bite of a blood-sucking

arthropod

(midges, mosquitoes, flies).

Dracunculus

infections are acquired through

ingestion of water

contaminated with

small crustaceans, Cyclops

spp., which

contain infective larvae.

Vector control;

protection of

well-water sources

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SectionIII– Parasitology By Nada Sajet

also

humans.

Cestodes,

Intestinal

The human serves as the

definitive host

for beef (Taenia saginata) and

pork

(Taenia solium) tapeworms;

cows/

camels and pigs serve as

intermediate hosts, respectively.

Humans also serve as the

intermediate host for T. solium

(cysticercosis). Diphyllobothrium

latum adult tapeworms can be

found

in a number of wild animals, the

most important being dogs, bears,

seals, and walruses, which serve

as

reservoir hosts; humans are the

definitive host. Hymenolepis

nana

(dwarf tapeworm) can occur in

rodents; humans can serve as

both

intermediate and definitive hosts,

with development from the egg to

adult worm occurring in the

human

intestine.

Human infection with the adult

worm

occurs through ingestion of raw or

poorly cooked meat (beef, camel,

pork)

containing the intermediate forms,

the

cysticerci. Humans become the

accidental intermediate host when

eggs

from an adult T. solium tapeworm

are

ingested. The cysticerci develop

in the

muscle and tissues of the human

rather

than the pig. Infection with the

adult D.

latum tapeworm occurs through

ingestion of poorly cooked

freshwater

fish containing the sparganum or

plerocercoid larval form. Infection

with

H. nana is primarily acquired

through

accidental ingestion of eggs from

an

adult tapeworm.

Adequate cooking of

infected

meat; treatment of patients

harboring adult tapeworms

(accidental ingestion of

eggs

can lead to infection

Cestodes,

Tissue

dult worms are found in a variety

of

animals; the human becomes the

accidental intermediate host after

ingestion of eggs from the adult

worms. Reservoir hosts include

dogs,

cats, and rodents

Ingestion of certain tapeworm

eggs or

accidental contact with certain

larval

forms can lead to tissue infection

with

Taenia solium, Echinococcus spp.,

and

several others.

Preventive measures

involve

increased attention to

personal

hygiene and sanitation

measures.

Trematodes,

intestinal

Fish-eating wild and domestic

animals

Ingestion of water chestnut and

caltrop

Avoiding eating raw water

plants

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SectionIII– Parasitology By Nada Sajet

serve as reservoir hosts. The

definitive host of Fasciolopsis

buski

is the pig.

(raw, peeled with the teeth) is the

source of infection; metacercariae

are

encysted on the plant material. Pig

feces are used to fertilize various

water

plant crops.

that may contain encysted

larval forms of the flukes;

adequate waste disposal of

farm animal feces (pigs).

Trematodes,

liver, lung

Cats, dogs, and wild fish-eating

mammals can serve as reservoir

hosts for Opisthorchis spp.,

Clonorchis sinensis, and

Paragonimus spp. Fasciola

hepatica

is normally a parasite of sheep,

and

F. gigantica is a parasite of cattle;

humans are accidental hosts.

Infection occurs through ingestion

of raw

or poorly cooked fish, crabs,

crayfish,

and certain plants in or on which

metacercariae are encysted.

Infection

with Fasciola spp. is not easily

acquired

(the parasite is not that well

adapted to

the human host).

Thorough cooking of

potentially

infected fish, crabs,

crayfish;

avoiding eating raw water

plants that may contain

encysted metacercariae.

Trematodes,

Blood

Schistosoma mansoni and S.

haematobium appear to be

restricted

to the human host; S. japonicum

can

be found in cattle, deer, dogs, and

rodents. The worms mature in the

blood vessels, and eggs make

their

way outside the body in stool

and/or

urine. The freshwater snail is a

mandatory part of the life cycle

(contains developmental forms of

schistosome).

Infection occurs through skin

penetration

by infected cercariae released

from a

freshwater snail containing the

intermediate stages of the

schistosome

life cycle. Cercariae can be

released

from the snail intermediate host

singly

or in groups

Protection from potentially

contaminated water sources;

awareness of mode of

transmission; proper

handling

of human waste containing

eggs (continued infection of

snail intermediate hosts).

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Section IV - Medical Mycology By Dr. Kareem Lilo

Introduction

Mycology is the study of fungi. The name “fungi” is derived from

“mykos” meaning mushroom. The fungi are eukaryotic organisms

and they differ from the bacteria, which are prokaryotic organisms,

in many ways . The fungi possess rigid cell walls, which possess two characteristic cell structures:

chitin and ergosterol.

Chitin: The fungi consist primarily of chitin, unlike peptidoglycan

present in cell wall of bacteria. Hence, fungi are not sensitive to action of penicillin and other

antibiotics that inhibit peptidoglycan synthesis. Chitin is a polysaccharide consisting of long chains

of N-acetylglucosamine. In addition to chitin, the fungal cell wall also contains mannan and other

polysaccharides. Of these, beta-glucan is most important, because it is the target of antifungal drug

caspofungin.

Ergosterol: The cell membrane of fungus contains ergosterol, unlike human cell membrane which

contains cholesterol. The antifungal agents, such as amphotericin B, fluconazole, and ketoconazole

have selective action on the fungi due to this basic difference in membrane sterols.

Fungal infections are mycoses . Most pathogenic fungi are exogenous, their natural habitats being

water, soil, and organic debris. Th e mycoses with the highest incidence— candidiasis and

dermatophytosis—are caused by fungi that are part of the normal human microbiota and highly

adapted

to survival on the human host. For convenience, mycoses may be classifi ed as superfi cial,

cutaneous, subcutaneous, or systemic, invading the internal organs ( Table 4-1 ). Th e systemic

mycoses may be caused by endemic fungi, which are usually primary pathogens, or by ubiquitous,

oft en secondary opportunistic pathogens.

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Taxonomical Classification

The fungi are placed in the phylum Thallophyta. There are four classes of fungi: Zygomycetes,

Ascomycetes, Basidiomycetes, and Deuteromycetes or Fungi Imperfecti .

Pathogenesis of Fungal Infection

Most fungi are obligate aerobes or facultative anaerobes, but none are obligate anaerobes. The natural

habitat of most fungi is environment, because all these fungi require a preformed organic source of

carbon, hence their constant association with decaying matter. C. albicans is exception and is an

important fungus, which is a part of the normal human flora. The effects of fungi on humans can be

grouped in three major ways as follows: (a) colonization and

disease, (b) hypersensitive diseases, and (c) diseases caused by

mycotoxins or fungal toxins.

Colonization and Disease

Most fungal infections are mild and self-limited. Intact skin is an effective host defense against

certain fungi. But if the skin is broken, organisms, the fungi enter through that broken skin and

initiate the infection. Fatty acid content, pH, epithelial turnover, and normal bacterial flora of the skin

contribute to host resistance against fungi. For example, the mucous membrane of the nasopharynx

Table(4-1)The Major Mycoses and Causative Fungi

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traps inhaled fungal spores. Cell-mediated immunity is much important in conferring protection

against fungi. Suppression of cell-mediated immunity can lead to reactivation and dissemination of

asymptomatic

fungal infection and to diseases caused by opportunistic fungi. The humoral immunity is mediated

by production of IgG and IgM antibody. But their role in protection from fungal disease is uncertain.

Fungal infection that occurs in the immunocompromised hosts is called as opportunistic mycosis.

Hypersensitivity Diseases

Humans are continually exposed to air-borne fungal spores and other fungal elements present in the

environment. These spores can be antigenic stimulants and depending on individual’s

immunological status may induce a state of hypersensitivity by production of immunoglobulins or

sensitized lymphocytes. Rhinitis, bronchial asthma, alveolitis, and various forms of atopy are the

clinical manifestations of hypersensitive pneumonitis. The clinical manifestations of the

hypersensitivity disease are seen only in sensitized person, after repeated exposure to the fungus,

fungal metabolites, or other cross-reactive materials. Allergies to the fungal spores are manifested

primarily by an asthmatic reaction including rapid bronchial constriction mediated by IgE,

eosinophilia, and positive hypersensitivity skin test reaction. These are caused due to immediate

hypersensitivity reactions of the host to fungal spores.

Diseases Caused by Fungal Toxins

Mycotoxicosis is caused by ingested fungal toxins. Mycotoxicosis