Parasit - Intro -Mbchb Modified-sept 2011 Sep (2)

8/12/2019 Parasit - Intro -Mbchb Modified-sept 2011 Sep (2)

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MEDICAL PARASITOLOGY

DR. NGETHE MUHOHO

( PhD Medical Parasitology)

September 2011


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WHAT ARE PARASITES?

The main parasites that you know of?

The main parasites in your area?

Which are parasitic disease outbreaks thatyou know of?


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What are parasites ?

All animals and plant forms originated and developed

as free-living organisms which were obliged tocompete with the others for existence.

Only those which were developed satisfactory

adjustment and adaptation were able to survive.

Among this group were many species in different

animal phyla of animal and plant kingdoms which

came to depend on their associates for survival

(shelter and food, reproduction) (Parasites).


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Parasite and parasite environment.

All animals and plant organisms that are not parasites

are usually hosts. Example. Human can be host for numerous parasites

like protozoa, intestinal worms, fleas, and lice and

mosquitoes


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Can parasites live inside our organs?

Alimentary tract 197 species

Cavities, organs, and

tissue

107 species

Circulatory system 21 species

Skin and tissues 56 species

Source: Journal of Parasitology85:379-403 Dr. D.W.T.

Crompton (Crompton, D.W.T. [1999] How much human

helminthiasis is there in the world?)

M it d f l b l iti


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Magnitude of global parasitic

infectionsDisease Human number

infected

Mortality Rate

All helminths 4.5 billion

Roundworms 1273 mil 20 thousands

Hookworms 1277 5060 thousands.

Whipworms 902 mil

Filaria worms 657 2050 thousands

Bilharziasis 200 mil 0.5 -1 mil

Malaria 489 ml 12 mil

Amoebiasis 50 mil 40 thousands


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A community identifying areas of open

defecation. to end open defecation (photo:

PlanInternat ional/Ethiopia)


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Parasites and human welfare.Human population has suffered greatly through the

centuries because of parasites: Examples

Fleas(parasites) transmitted bacteria destroyed

a third of population in Europe in 17thcentury

(Fleas transmitted plague) Body louse typhus fever determined fate war in

many battles fields as recent as World war 2.

During the Spanish siege lost 3,000 army menlost to enemy action but an additional 17,000

died of typhus fever transmitted by Body louse.

Malaria is causing havock in many developing

countries..


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World war 1 - typhus caused at least 3

million deaths out of 2030million cases

Word war ll. Epidemic outbreaks of typhusoccurred in many fronts with devastating

results especially in detention camps

Malaria, Bilharziasis outbreaks havecaused abandonment of many new

agricultural developments


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Common terms about parasite:

Common terms epidemiology of parasitic infections.

Host--,

Intermediate hostmaintain the immature stages of parasite

Definitive or primary host- Final host- Mature of parasitestage

Reservoir host- Animal host maintaining parasite inenvironment- transmissible to man

Paratenic host- Transport host

Life cycle-All atages of life of the parasites..

Infective stage-

Zoonosis-


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Parasite host interrelationship

Symbiosis is the close association of

parasite and the host:

Commensalism

If a parasite derives nourishment without

reciprocating and without injury to the host

Mutualism- If the relationship is beneficial to

both the parasite and the host


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Parasitism: the relationship in which the parasiteuses the life cycle of the host species for

sustenance or reproduction, or both.The process harmful or disease causing

to the host

Parasitism is not based on the parasite killing thehost, as in predation.

Death of the host may occasionally occur as aconsequence of parasitism, but it is in theparasites best interest to keep the host alive.


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Parasite host interrelationship.

Parasites themselves are hosts of other parasites Eg. Mosquitoes and ticks carrying parasites of humans

Clinical parasitology is concerned with the animalparasite of man and their medical significance as well

as their importance in human communities


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Definitions of terms commonly used in

parasitology

Parasitology:

Parasitology is the area of biology

concerned with the phenomena of

dependence of one organism on another

The parasite lives on or in the host usually alarger organism which provides physical

protection and nourishment


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Definition of Medical

Parasitology/ parasitologist

Medical Parasitology

Parasites Parasitic diseasesMorphology

Life

Cycle

Pathogenesis

Diagnosis

Treatment

Transmission

Pre

vention

G O


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Parasitology: General Introduction and Orientation

1. Parasite and its environment

2. Epidemiology and Geographical Distribution

3. Nomenclatural aspect of animal species Responsible forHuman Disease

4. Disease process due to animal agents and their clinical

manifestations- - acute or chronic

5. Diagnosis: 1) Clinical diagnosis 2) Laboratory diagnosis6. Treatment of Diseases due to animal parasites or

transmitted by animal vectors

7. Control and Prevention of Diseases caused by parasites

or transmitted by vectorsSpecifics

1. Protozoa and Protozoa Infections

2. Helminths and Helminthic Infections

3. Arthroponds and Human Disease.


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Parasitism and epidemiology of disease

Epidemiological information of the disease isimportant to device schemes for control ofinfections

Epidemiology the study of endemic diseases-

factors involving establishment and sustaining ofparasitic disease in the community

Distribution = Pattern of disease in community

Prevalence =(No. infected/No. examined x 100) Intensity = Measurable indicators E.g. parasitemia

or No. of parasitesper given volume of specimen

Incidence- (No. of new cases per year).


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Environmental and ecological conditions Can the parasite survive in the environment

Presence of the intermediate host

Favourable environment conditionsweather

soil, water etc. eg. Schistosomiasis in slow orstationary water, Malaria in wet humid tropicalregions

sociological factors crowded places eg in theslums, institution like jails, orphanages etc

Common terms about parasite: host, intermediate host, final host, reservoir host, paratenic host, life cycle, infective stage, zoonosis.


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Human behaviorPractices, attitudes,knowledge Eg eating of raw beef

ClimateDry weather, wet weather favoringdevelopment of parasites

Local traditionEating habits-Raw meat, nightsoil farming

Parasite life cycle- presence of parasite inhuman host presence of intermediate host orhost in the environment Stages ofdevelopment in the host and outside the

host Infectivity of parasite.

Diseases establishment in the host..etc

Common terms about parasite: host, intermediate host, final host, reservoir host, paratenic host, life cycle, infective stage, zoonosis.


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Endemic- When the prevalence maintains arelatively steady or moderate level

Hyperendemic- if the prevalence is high

Epidemic- If there is a sharp rise in the incidenceor an outbreak of considerableintensity

Sparodic- If the disease apppears occasionalyand in of or at most a fewmembers of communities

Methods of epidemiology


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Types of parasites:

Obligate: Parasite cannot exist without the

hoste.g. Trichinella spiralis,plasmodiumspecies, Trypanosomes

Facultative parasitesThose which, underfavourable condition may live a parasitic life or a

free-lifeeg. Strongyloides stercoralis andhookworm

Opportunistic parasites These are free-living butcan turn out to be parasitic in favourable

conditionseg. Naegleria gruberi,Acanthamoeba spp(CommensalsBalanditium coli, Endolimax nana )


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Endoparasite and ectoparasite

A parasite which lives in or on the body ofthe host is called endoparasite (protozoa

and heminthes)

EctoparasiteThose which are attachedto to the skin or temperarily invade the

superficial skin tissue of the host..

(arthropodsFleas, bedbugs lice).

Temporaryparasites like mosquitoes and

fleas


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Host and type of host

Host:An organism that harbors the parasiteusually larger than the parasite.

.

Intermediate host : The host harboring thelarvae or asexual stage of parasite.

Primary host : The host harboring adult or

sexual stage of parasite. Reservoir host : Animals harboring the

same species of parasites as man.

Potential sources of human infection.


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SINGLE HOST PARASITES

Require one host only to complete the life

cycle.

B. Examples: 1. Protozoa - the amoebae,

G. lamblia, Trichomonas, Cryptosporidium.

2. Helminths -Ascaris, Trichuris,

Enterobius, Strongyloidesetc


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MULTIPLE HOST PARASITES

Require more than one host to complete the life

cycle. 1. Definitive host: site of sexual reproduction

2. Intermediate host(s):site of asexualreproduction or larval development

3. The distribution of non-human intermediatehosts may be important in epidemiology of thedisease.

Examples: 1. Protozoa - Leishmania,Trypanosoma, Plasmodia, Toxoplasma

2. Helminths - Clonorchis, Paragonimus,Schistosoma, Taenia, Diphyllobothrium


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Life cycle and type of life cycle

What is a parasitic life cycle:

Life cycle : The whole process of

parasite growing and developing.

Direct life-cycle : Only one host (no

intermediate host).

Indirect life cycle : Life cycle with more

than one host (intermediat host and

final host).


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Definition of Medical

Parasitology

Medical Parasitology

Parasites Parasitic diseasesMor

phology

Life

Cycle

Path

ogenesis

Diagnosis

Trea

tment

Transmission

Prevention


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HOST PARASITE INTERELATIONSHIP- Someparasites require only one host e.g.

Giardia lambliaand

Human body or Head louse (Pediculushumanus) and human body

Certain anophelene mosquitoes haveprevalence for human blood (anthropoplic)

Other parasites are less discriminating andhuman constitute one of several hosts(eg.Clonochis sinensis, Schistosoma jopanicum andTrichinella spiralis)


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Host parasite relationship2

In other cases, domestic and wild animalsserve as the reservoir of the parasite and

man is only an incidental host eg.

Echinoccocus granulosus (Zoonosis)Zoonosis- Diseases of animals which

are transmitted to man


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Zoonosis classification

1. Euzoonosis--Parasitosis common to the man

and the reservoir2. ParazoonosisMan is an incidental host

3. AnthropozoonosisInfection acquired byman from other vertebrates(eg. Trichinosis

or cysticercosis of swine tapeworm, anthrax)Or a the infections transmitted by arthropodsor molluscan intermediate hosts

4. AmphixenosisDiseases common to manand other vertebrates

5. AnthroponosisDiseases presentlyrestricted to man but which evolved from otherhost sourceseg


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Ecological and evolutionally aspect ofhost-parasite relationship

Infections are maintained among animalsand hosts and vectors under specificecological conditions: Eg

1)Schistosoma infection in slow running

water where the vector fresh water snailsthrive.

2) River blindness in regions where black flybreeds in fast flowing water


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Ecological and evolutionally aspect of host-parasite relationship

Modern civilization tend to disrupt the natural

course of euzonoses so that man becomesinvolved in their cycle, at times with disastrousconsequences. E.g:

Hydroelectric dams and new farming irrigationdevelopment creating environment for waterborn diseases

Diseases in new human settlements

Yellow fever outbreaks in Rift Valley causedby Invasion of Ndoinett Forest by political

gangs Cholera outbreaks in informal settlements

(slum) in Towns and Cities

.


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Epidemiological information of the disease isimportant to device scheme for control ofinfections

Epidemiology the study of endemic diseases-

factors involving establishment of parasiticdisease in the host and sustaining oftransmission in in the environment.

I t t id ti f iti di


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Important considerations for any parasitic disease

Epidemiology: Geographical location and the

distribution of the non-human host influence thedistribution of parasitic disease: Eg.

Wild animals help the spread ofTrypanosoma gambiense infection

Mode of Transmission/ Portal of infection:

Direct inoculation---Hookworm

Insect inoculationMalaria/Filariasis

Ingestion of infective forms in uncooked foodor contaminated waterTrichinella spiralis andtapeworms

Sexual intercourseTrichomonas

Fecal-oral transmissionRoundworms


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Diseaseprocess & Clinical

manfestatioms1. Parasite carrier host: Parasite may live on or in

the tissue of the host without causing any

evident harm.

Parasite carrier-Tissue repair is as rapidly asits destruction-- the host is a carrier.

2. Parasitic Disease:

The parasite may cause considerable harm

including death to the host.

Disease in the host (Parasitosis)


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Disease in the host (Parasitosis)

Parasitosis -When parasite become a

pathogen and causes damage to the host.1.Damage-- Lesions localized at the point of

establishment or extended to other regions

2.Damage may be in form of:

a.Trauma or physical damage

b.Lytic necrosis-

c.Stimulation of host tissue reaction

d.Toxic and allergic reaction

e.Allowing secondary infections

Di i th h t


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Disease in the host

Parasitosis-

.Damage may be in form of:

a.Trauma or physical damage__ Eg. Skin

lesions by mosquitoe scabies,

b.Lytic necrosis---Enzymes of amoeba

eating away the tissue- leading to

diarrhoea and dysentery


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Parasitosis-

2. Stimulation of host tissue reaction- immune

cells- cellular proliferation and infiltrationaround the parasite- enveloping fibrosis of

the tissue.

3. Toxic and allergic reactions Direct introduction of venoms by insects etc,

Effects of secretions from adult parasites, eg

busting of hydatid or parasite metabolites may

cause hypersensitivity

4. Secondary infections- Damage in the tissue by

parasite may allowing entry of pathogenic bacteria

in the tissue- Tetanus, Staphylococcus spp. Inf.


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Immunity to parasitic infections

No immunity to subsequent exposures(exemption to Cutaneous leishmaniasis)

Most have ability to alter antigensity- e.g..

Adult helminths, trypanosome etc.Constant exposure may how confer a

degree of immunity, e.g. New comers

become infected soon after first exposures

Parasitemia may also be very high without

symptoms in the local persons in malaria


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Parasitism & Malnutrition

Polyparasitism is common in endemic areas

Total Pathologic effect to polyparasitism in an

individual may lead to malnutrition:

Examine sharing of nutrients, e.g in helminth,

Imbalance of the systems due tissue damage

etc


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Clinical Evidence of parasitism

Clinical Manifestations:

Is the infection symptomatic?

Are unusual symptoms a part of the

clinical picture?

Clinician experience on the parasitic diseases

Symptoms of the disease and history of thepatientis he from an endemic area or the

source of exposure.


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Pathology:

1. Organs and tissues involved in each parasiticinfection.

2. Mechanism of disease Allergic host response

Mechanical tissue damage

Inflammatory host response -

Mass effect - overwhelming effect on host

3.Classic lesionscharacteristic like those


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laboratory diagnosis

Evidence by laboratory diagnosis:Clinician must be familiar with the methods

for diagnosis and the type of specimen

required. The specimen must be flesh andto be processed immediately.

Preserve the specimen if not to be examined

immediately

Blood smears for microscopy must be

prepared on clean microscope glass slides


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Laboratory Diagnosis:

1. Parasites are not commonly diagnosed

by culture2. Microscopic examination

Stool - examination for ova and parasites

Blood films

Biopsies

Sputum and bronchoalveolar lavage

Vaginal secretions - examination for ova

and parasites

Treatment:


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Treatment:

Points to consider before treatment:

1. Severity, intensity, duration of the infection and

probability of infection

2. Efficacy, availability, toxicity and acceptability of

the treatmentChemotherapy- There are many synthetic drugs

available

Surgical interventions- Where drugs are not viable

eg. Cysticercus cellulosae in the brain eye etc

.


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Parasite Control and prevention

An involvement of physician and other public

health personnel in:

1.Reduction of morbidity by treatment of

disease

2.Control of disease from community level

3.Prevention of transmission of the disease by

repression of causative agent in the field

El t f it t l


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Elements of parasite control measures

1. Detection and accurate diagnosis and

evaluation of clinical importance of disease2. Adequate treatment of patient

3. Search and treatment of other cases

4. Determination of source of infection andreport to health officials

5. Advise families on how to avoid exposure

6. Support preventive measures in the comm.

7. Education to the community to improve on

health awareness

Parasit - Intro -Mbchb Modified-sept 2011 Sep (2)

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