Parasites

Question 1

What is parasitology?

Answer 1

The branch of medical sciences dealing with organisms (parasites) living in or on other organisms (hosts) and causing harm (disease) to them

Question 2

Host (definition)

Answer 2

An organism that harbours other organisms, which may or may not be pathogenic

Question 3

Human Parasites – 3 types

Answer 3

1. Helminths (worms)
2. Protozoa (unicellular)
3. Arthropoda (arthropods)

Question 4

Classification of Parasites (Habitat) - Ectoparasites vs. Endoparasites

Answer 4

Ectoparasites - live ON the surface of their host (INFESTATION)
Endoparasites - live INSIDE the body of their hosts (small intestine, large intestine, bile duct) (INFECTION)

Question 5

Classification of Parasites (Survival With or Without a Host) - Obligatory vs. Facultative

Answer 5

Obligatory - can’t survive outside their hosts, i.e. completely dependent on their hosts
Facultative - capable of free living outside their host (change lifestyle between free-living and parasitic)

Question 6

Temporary vs Permanent vs Accidental vs Opportunistic

Answer 6

Temporary: visit the hosts from time to time for its meal (ex. blood sucking mosquitos)
Permanent: always fixed to their hosts (ex. most parasitic worms) AKA obligatory
Accidental: affect unusual hosts
Opportunistic: capable of producing disease in immuno-compromised host

Question 7

Types of Hosts: DH, IH, RH, Vector

Answer 7

Definitive Host (DH): harbours the adult stages or sexually reproducing forms of the parasite 
Intermediate Host (IH): harbours the larval stages (immature stages) or asexually reproducing form 
Reservoir (RH): harbours the same species and stages as human. It maintains the life cycle of the parasites in nature and acts as a source of re-passing infection to man
Vector = an arthropod that transmits parasites from one host to another

Question 8

Marlaria Life Cycle

• How many hosts?
• Sexual or asexual?

Answer 8

Life cycle occurs in 2 hosts (DH and IH)

Life cycle has a sexual (DH) generation, alternating with an asexual (IH) one

Question 9

Malaria: explain the DH and the IH

Answer 9

DH = invertebrate (female mosquito) = sexual reproduction
IH = vertebrate (man) = asexual multiplication cycles

Question 10

All vectors are ______?

Answer 10

Arthropods

*But not all arthropods are vectors!

Question 11

Vector (definition)

Answer 11

Arthropods that transmit pathogenic microorganisms to man

Question 12

Types of Vectors - Biological & Mechanical

Answer 12

Biological (essential in life cycle)

1. Propagative (viruses), when the parasite increase in number inside the vector
2. Cyclo-developmental (filaria), developmental changes occur, but no change in numbers
3. Cyclopropagative (protozoa), combination of both, multiply in numbers and developmental changes

Mechanical (NOT essential in life cycle)

Question 13

HELMINTHS (worms)

Answer 13

Multicellular
Eukaryotic 
PLATYhelminthes (flat worms) 
-No body cavity
-Hermaphrodite (M & F sex organs) 
-----Trematodes
-----Cestodes 
NEMATthelminthes (round/cylindrical worms) 
-Body cavity 
-Male & female

Question 14

Life Cycle of Helminths (3 main stages)

Answer 14

Helminths reproduce by egg laying
Helminths form 3 main life-cycle stages: 
1. Eggs
2. Cercaria/metacestode/larvae
3. Adults 

Transmission is via EGG
Infection is via INTERMEDIATE STAGE
Adults are the DH (man)

Question 15

General Characteristics of Protozoa

Answer 15

• Eukaryotic
• UNIcellular
• Microscopic
• Sexual OR asexual reproduction
• GI or tissues infections

Question 16

4 Classifications of Protozoa (according to organ of locomotion)

Answer 16

1. Amoeba (pseudopodia)
2. Ciliates (cilia)
3. Flagellates (flagellum)
4. Sporozoa (apical complex)

Question 17

Reproduction in Protozoa

-Asexual vs Sexual

Answer 17

Asexual = binary fission & schizogony (merogony) 
Sexual = copulation/syngamy

Question 18

Life Cycle of Protozoa

• Trophozoite stage
• Cyst stage

Answer 18

Trophozoite = motile

Cyst - resistant, resting

Question 19

Modes of Transmission

Answer 19

-Faecal-Oral Transmission = environmentally-resiststant cyst stages passed in faeces of one host & ingested with food/water by another
-Direct Transmission
-Vector-borne Transmission: of trophozoites taken up by blood-sucking arthropods and passed to new hosts they they next feed
Transplancental - placenta -> baby; TORCH infections

Question 20

Arthropods

Answer 20

Several parasitic insects, ticks and mites (ectoparasites), act as vectors transmitting disease from one host to another
*NOT all parasitic insects can act as vectors

Question 21

Diagnosis of Parasitic Infections

Answer 21

1. History & Clinical Examination
2. Laboratory
   - -Blood tests (eosinophilia, seen in most tissue invading helminths)
   - -Microscopy (stool exams, blood parasites, biopsy samples for tissue parasites)
   - -Serology (parasite antigens, antibodies)
3. Radiology (calcified larvae in tissues, space occupying tissue parasites)

Question 22

Disease Control

Answer 22

Health education!
Control reservoir host!
Interrupt life cycle!
-Interrupt mode of infection
-Intermediate host control 
Treat patients! 

Treatment: antihelminthics, antiprotozoals