C4: Sources of Exposure, Epidemiology, Mode and Route of Transmission of Parasitic Infection Flashcards
Name the SOURCES OF INFECTION
Contaminated soil and water
Food
Animal
Vectors
The infection which is transmitted from infected animals to humans is called as
.
zoonoses
A ________is an agent, usually an arthropod that transmits an infection from man to man
or from other animals to man, e.g. female Anopheles is the vector of malarial parasite.
vector
The term ______refers to a vector, which not only
assists in the transfer of parasites but the parasites undergo development or
multiplication in their body as well. They are also called as ______.
biological vector ; true vectors
The term ________ refers to a vector, which assists in
the transfer of parasitic form between hosts but is not essential in the life cycle of the
parasite
mechanical vector
This interval between the entry of the parasite into the vector and the lime it takes to become
capable of transmitting the infection is called the
extrinsic incubation period.
A person who is infected with parasite without any clinical or subclinical disease is
known as ___. He can transmit parasite to others.
carrier
- It is the most common mode of transmission of the parasites. Infection is transmitted
orally by ingestion of food, water or vegetables contaminated with feces containing the
infective stages of the parasite. (e.g., cysts of E. histolytica, and ova of Ascaris
lumbricoides).
Oral or feco-oral route:
:
- Infection is transmitted by the penetration of the larval forms of the parasite through
unbroken skin (e.g., filariform larva of Strongyloides stercoralis and hookworm can
penetrate through the skin of an individual walking barefooted over fecally
contaminated soil), or by introduction of the parasites through bloodsucking insect
vectors. (e.g., Plasmodium species, Leishmania species and Wuchereria bancrofti)
Penetration of the skin and mucous membranes
- Finger-to-mouth transmission
Self(autoinfection):
is the most frequent parasite to be transmitted by sexual contact.
Trichomonas vaginalis
- Mother to fetus transmission is important for few parasitic infections like Toxoplasma
gondii , Plasmodium spp. and Trypanosoma cruzi.
Vertical transmission:
Many parasitic diseases are transmitted by insect bite such as: malaria (female
anopheles mosquito), filariasis (Culex), leishmaniasis (sandfly), Chagas’ disease
(reduviid bug) and African sleeping sickness (tsetse fly)
Bite of vectors
- Certain parasites like Plasmodium species, Babesia species, Toxoplasma species,
Leishmania species and Trypanosoma species can be transmitted through transfusion
of blood or blood products
Blood transfusion:
Example of true vectors are:
* Mosquito: ______, ______
* Sandflies: _____
* Tsetse flies: _______
* Reduviicl bugs: ______
* Ticks: ______.
Example of true vectors are:
* Mosquito: Malaria, filariasis
* Sandflies: Kala-azar
* Tsetse flies: Sleeping sickness
* Reduviicl bugs: Chagas disease
* Ticks: Babesiosis.
Example of mechanical vectors is:
* Housefly:
Amebiasis
Enumerate how the parasites can cause damage to humans in various ways.
Mechanical trauma
Space occupying lesions
Inflammatory reactions
Enzyme production and lytic necrosis
Toxins
Allergic manifestations
Neoplasia
Secondary bacterial infections
- Certain parasites produce characteristic cystic lesion that may compress the surrounding tissues or organs, e.g., hydatid cysts and neurocysticercosis
Space occupying lesions:
- Most of the parasites induce cellular proliferation and infiltration at the site of their multiplication, e.g., _______provokes inflammation of the large intestine leading to the formation of ____. Adult worm of W. bancrofti causes mechanical blockage and chronic inflammation of the lymphatics and lymph vessels. Trematode eggs can induce inflammatory changes (granuloma formation) surrounding the area of egg deposition
Inflammatory reactions; E. histolytica; amoebic granuloma
- Obligate intracellular parasites of man (Plasmodium, Leishmania and Trypanosoma), produce several enzymes, which cause digestion and necrosis of host cells. E. histolytica produces various enzymes like cysteine proteinases, hydrolytic enzymes and amoebic pore forming protein that lead to destruction of the target tissue
Enzyme production and lytic necrosis:
:
- Some of the parasites produce toxins, which may be responsible for pathogenesis of the disease, e.g., E. histolytica. However, in contrast to bacterial toxin, parasitic toxins have minimal role in pathogenesis
Toxins
- Many metabolic and excretory products of the parasites get absorbed in the circulation and produce a variety of allergic manifestations in the sensitized hosts
Allergic manifestations:
Examples include schistosomes causing cercarial dermatitis, rupture of hydatid cyst producing anaphy lactic reactions and occult filariasis (tropical pulmonary eosinophilia)
Allergic manifestations:
- Some of the parasitic infections can contribute to the development of ____(e.g., S. haematobium causes bladder carcinoma, Clonorchis and Opisthorchis cause cholangiocarcinoma)
neoplasia
- Seen in some helminthic diseases (schistosomiasis and strongyloidiasis).
Secondary bacterial infections:
Ingestion of raw or undercooked meat harboring infeclive larvae (measly pork containing ________, the larval stage of Taenia solium)
cysticercus cellulosae
______ causing cercarial dermatitis, rupture of hydatid cyst producing _________ and occult fi lariasis (tropical pulmonary eosinophilia)
schistosomes; anaphylactic reactions
