The document covers the field of parasitology, focusing on the study of parasites, their hosts, and the relationships between them. It details the history, definitions, classifications, sources of infections, modes of transmission, and the effects of parasites on their hosts, as well as factors influencing susceptibility to infections. Additionally, it outlines the immune evasion strategies of parasites and concludes with assignments for identification of various parasites and sources of specimens.

1. PARASITOLOGY AND LABORATORY
TECHNIQUES 1
MWANAHAWA JUMA

2. INTRODUCTION
• Parasitology- is the study of parasites , their hosts and
relationship between them
• It is also the study of small organisms (parasites) living on
/in other organisms(host), regardless of whether the effect
on the host is beneficial , neutral or harmful.

3. HISTORY OF PARASITOLOGY
• Pioneer Dutch Microscopist Antonie Von Leeuwenhoek of Holland
introduced single lens microscope and observed guardia in his own
stool in 1681.
• Louis Pasteur- first published scientific atudy on a protozoal disease
leading to its control and prevention during investigation of an
epidemic silk worm disease in South Europe in 1870.
• 1878- Patrick Mason discovered the role of mosquitoes in filariasis,
a first evidence of vector transmission.
• 1880- Laveran in Algeria discovered Malaria parasite
• 18877-Ronald Ross and Calcuta showed its transmission by
mosquitoes

4. DEFINITION OF TERMS
• Parasite-living organism which depends on a living host
for the nourishment and survival whether temporarily
/permanently
features of parasites
smaller than their hos
outnumber the host
short life span than the host
have greater reproductive potential than their host

5. definition of terms
• Host-An organism which harbors the parasite and
provides norishment and shelter to the latter and is
relatively larger than the parasite
types of host
a) definitive host- its either a host that harbors the adult
stage of the parasite or most highly developed form of the
parasite occurs; or sexually mature stages of a parasite
and fertikization takes place in it .
defined also as the host in which the adult parasite lives
and undergoes sexual reporduction eg mosquito is the
definitive host for malaria

6. continuation of type of host
b) Intermediate host- the host in which the larval stage of
the parasite lives or asexual multiplication takes place.
May be 2/more host required to complete different larval
stages known as 1st and 2nd intermediate host.
c) Reservoir host- a host which harbors the parasite and
acts as an important source of infection to other
susceptible host eg dog-hydatid disease
d) Accidental/Incidental host- infection of a host other than
the normal host species eg man -cystic
echinococcosis(dog)
e)

7. Definition of terms
e)Paratenic /carrier host- a host in which larval stage of the
parasite remains viable without further development but can
transmit the infection to another host
• Vector- any arthropod /other living carrier which
transports a pathogenic microoganism from an infected to
non-infected host.
types of vectors
a) biological vector-completes the life cycle of a parasite eg
anopheles(mosquito)
b)mechanical(paratenic/transport) vector- passive carriers
of parasites;not essentially the life cycles eh
housefly/coakroach in the transmission of amoeba

8. definition of terms
• infection-invasion of the body by a pathogenic organism
(execept arthroprds) and the recation of the host tissue to
the presence of the parasite or related toxins
• infective stage- the stage of parasite at which its capable
of entering the host and continue development within the
host
• diagnostic stage- a developmentage stage of a
pathogenic organism that can be detected in stool, blood,
urine, sputum, csf or other human body secretion
• infestation- the establishment of arthropods upon/ within
a host
•

9. • zoonosis- diseases of animal- term is applied to those
diseases that are transmittable to man
• biological incubation(prepatent )period- is the time
elapsing between initial infection within the parasite and
demonstaration of the parasites or their stages in
excreta,blood, aspirate and other diagnostic matter
• clinical incubation period- is the interval between
exposure and earliest manifestaion or infestation
• auto infection- an infected individual acts as a source of
hyperinfection to himself

10. • retro infection-a retrograde infection caused by the
newly hatched larva of e. vermicularis from the perianal
region to reach the colon , where the adolescent form of
the parasite develops
• super infection/ hyperinfection-when an individual
harboring the parasite is reinfected by the same parasite

11. CLASSIFICATION OF PARASITES
a) According to their habitat
i. Ectoparasite -parasite living on / affecting the skin surface of the host
eg lice
ii. Endoparasite- parasites living within the body of the host eg ascaris
subdivided into :
• obligate parasite- parasite which cannot exist without a host eg gondii
• facultative parasite-may live as a parasite or free living form
• accidental parasite- affects unusual host eg echinococcus
• aberrant parasite-infects host but cannot develop further eg dog
roundworms in humans
i. Free living parasite- non parasitic stages of active existence, while
living independently of the host eg cystic stage of naegleri floweri

12. continuation
b) According to the dependence of the host
i. Permanent /obligate parasite- parasite depends completely upon its host for metabolites,
shelter and transportation. this parasite cannot live outside its host eg plasmodium
ii. Temporary / facultative parasite- parasite is capable of independent existence inaddition to its
parasitic lifeeg strongyloids stercolaris
c) According to their pathogenicity
ii. Pathogenic parasite- causes disease in the host eg e. histolytica
iii. Non pathogenic /Commensal parasite- derives food and protection from the host without
causing harm to the host eg e. coli
iv. Opportunistic parasite- causes mild disease in imunologically healthy individuals ,but they
cause severe diasease in immuno deficient host eg toxoplasmosis gondii

13. SOURCES OF INFECTIONS
a) Contaminated soil- soil polluted with human excreta is
commonly responsible for exposure to infection with
the case of ascaris,ttrichuris and hook worms
b) contaminated water- may contain;
 viable cysts of amoeba, flagellates
cercarial stages of human blood fluke
cyclops containing larva of dranculus medinesis
fresh water worms -source of fishtape worms and
intestinal fluke infection
crabs/cray fishes- source of lung flukes
water plants- source of fasciolopsis buski

14. continuation
c) Insufficiently cooked meat eg pork and beef which contains
infective stages of the parasites eg taenia species
d) blood sucking arthropods- are responsible for transmission of :
malaria parasites by female anopheles mosquito
leishmania by phlebotomus
trypanosoma by tsetsefly
e) Animals
dogs -source for human infection with the hydatid cyst caused by
e. granulosus
herbivores animals-source for human infection with trychostronglus
species

15. continuation
f) Humanbeings- another person clothing, bedding or
immediate environment that he contaminated are directly
responsible for all or a considerable amount of infection
with pathogenic amoeba; e histolytica
g) sexual intercourse - trichomonas vaginalis
h) Auto infection- e vernicularis

16. MODES OF TRANSMISSION
a) Direct modes of transmission- the parasite doesnt
require biological vector and/or intermediate hosts and
only require a single host to complte its life cycle. may
use mechanical vectors for transmission
classified as :
 horizontal direct mode- mainly effected through:
fecal oral route(common); sexual inetercourse; blood
transfusion; direct skin penetration
vertical direct mode- transmission to the parasite is from
mother to child through: congenital/transplacental;
transmammary(breastmilk)

17. Modes of transmission
b) Indirect mode of transmission- the parasite has
complex life cycle and requires biological vectors and/or
one or more intermediate host for transmission

18. ROUTE OF TRANSMISSION
1) oral transmission- through food, water or hands eg
e.histolytica; raw /undercooked meat; undercooked
fish, crab or vegetation
2) skin transmission-fecally polluted soil eg hookworms;
water containing infective stages of the parasite
3) vector transmission- insect bite eg malaria
4) direct transmission- sexually or
kissing/transmammary/transplacental
5) inhalation of contaminated air- e vermicularis

19. HOST PARASITE RELATIONSHIP
1. Symbiosis-both host and parasite are dependent upon
each other. none of them suffers any harm from the
association
2. Commensalism- only the parasite derives benefit from
the association without causing any injury to the host.
a commensal is capable of living an independent life
also
3. parasitism- the parasite derives benefits and the host
is always harmed due to the association. the parasite
cannot live an independent life

20. Effects of parasites on their hosts
Affected in the foloowing ways:
 consumption of the nutritive elements of the host eg
hookworm sucks blood
obstruction of passages eg ascaris may cause i.o
bleeding eg schistosoma eggs
 destruction of tisssues eg trophozoites of e histolytica cause
liver cirhosis
compression of organs eg hydatid cyst in liver while pressure in
brain
release of toxic substances causes anaphylactic shock
pathway to secondary infections
allergy development eg arthropode bite
transmission of pathogens to man eg lice transmitting rickettsia

21. continuation to effects of parasites to hoat
predisposition to malignancy eg the case of bilharzia
chronic immune stimulation leading to unresponsiveness
to infections

22. Host Suspectibility factors
Host factors
genetic constitution
age
sex
level of immunity; natural and acquired
nutrition(malnutrtion / under nutrition)
intensity and frequency of infections
presence of co existing condition or disease that reduces immune
response eg pregnancy /hiv
lifestyle and occupation

23. parasite factors
strain of the parasite and adaptation to human host
parasite load/number
site(s) occupied in the body
metabolic process of the parasite -nature of any waste
products or toxins produced by the parasite during
growth and reproduction

24. Escape mechanism of parasite from the immune system
parasites can evade the host immune responses by variety
mechanism:
 site
 avoidance by recognition
 suppression of immune response

25. ASSIGNMENT
1. Mention possible parasites that are found in the following
specimens
a) stool
b) blood
c) urine
d) sputum
e) csf
2. identify the possible sources of specimen for the following
parasites

26. a) schistosoma mansoni
b) e. vermicularis
c) trypanosoma species
d) filaria worms
e) guardia lamblia
3. parasites that have indirect life cycles are more difficult
to control. why?