Parasitology πͺ± Flashcards
1
Q
What is a parasite?
A
An organism that lives in or on another organism (its host) and benefits by deriving nutrients and protection at the otherβs expense.
2
Q
What are the types of parasites?
A
1- obligatory parasites 2- facultative parasites 3- accidental parasites 4- endoparasites 5- ectoparasites 6- specific parasites 7- temporary parasites 8- saprozoic (spurious) parasites
3
Q
What are obligatory parasites?
A
They are parasites that canβt complete their life-cycle without exploiting a suitable host, If obligatory parasites canβt obtain a host it fails to reproduce.
4
Q
What are facultative parasites?
A
can either live freely (in soil or water) or as parasites in hosts when unfavorable environmental conditions occur.
5
Q
What are accidental parasites?
A
free-living organisms which enter the human body by mistake e.g. larvae of flies which are accidentally ingested and live in the intestine of man.
6
Q
What are temporary parasites?
A
visit its host from one time to another for feeding then leave.
7
Q
What are specific parasites?
A
affects only one host species.
8
Q
What are caprozoic (spurious) parasites?
A
a parasite species foreign to the host which has just passed through the alimentary canal without infecting the host. (For example, parasite eggs in the animal liver).
9
Q
What are ectoparasites?
A
a parasite that lives on the outside of the host.
10
Q
What are endoparasites?
A
a parasite that lives within the body of the host.
11
Q
What are the types of hosts?
A
1- Definitive host 2- Intermediate host 3- Reservoir host 4- Paratenic (transport) host 5- Vector host 6- Dead-End host
12
Q
What is a definitive host?
A
Host in which the parasite reaches its sexual maturity (adult stage).
13
Q
What is an intermediate host?
A
a host in which the immature (larval, not adult) stage of the parasite is found, or in which the parasite multiplies asexually.
Also termed amplifier host.
14
Q
What is a reservoir host?
A
An animal that harbors the parasite and acts as a continuous source of human infection.
15
Q
What is a paratenic host?
A
a host that harbors a parasite in an arrested state of development but the parasite remains alive and viable, ready to infect a subsequent suitable host.
16
Q
What is a dead-end host?
A
- a host from which infectious agents are not transmitted to other susceptible hosts.
- It means that the infection chain ends at that particular host, and further.
17
Q
What is a vector?
A
arthropod host that transmits the parasite from one host to another.
18
Q
What is the definition of host-parasite interactions (symbiosis)?
A
A relationship between two or more organisms that live closely together.
19
Q
What are the types of host-parasite interactions?
A
- Parasatism
- Commensalism
- Mutualism
- Phoreisis
20
Q
What is parasitism?
A
one of the two organisms (parasite) benefits, as it gains protection and nutrition at the expense of the other (host) that suffers from such association.
21
Q
What is commensalism?
A
both organisms live together and the commensal organism benefits without causing harm to the other.
22
Q
What is mutualism?
A
both organisms benefit from the association to an extent that both canβt live separately (a flagellate in the intestine of termite that feeds on wood).
23
Q
What is phoresis?
A
- In phoresis, there is no dependency but just carriage (Dientamoeba fragilis on Enterobius egg).
- phoront is usually the smaller organism and is mechanically carried by the other which is usually large.
24
Q
What is zoonoses?
A
infectious diseases that can be naturally transmitted between animals (usually vertebrates) and humans.
25
What are the types of zoonoses?
ANTHROPOZOONOSIS
| ZOOANTHROPONOSIS
26
What is anthrozooponosis?
a zoonosis maintained in nature by animals and transmissible to humans.
27
What is zooanthroponosis?
parasitic infections naturally maintained by humans but can be transmitted to other vertebrates.
28
What is anthroporosis?
Anthroponosis is another term where parasitic infections are found in man alone.
29
What is the classification of zoonotic disease?
According to the source of infection: feral (sylvatic) or domestic
According to the method of transmission: direct zoonosis - meatzoonoses - saprozoonosis
30
What is feral (sylvatic) zoonoses?
- the source of infection is a wild animal with no close relationship to man.
- Humans become exposed to infection in the course of hunting.
31
What is direct zoonoses?
Infection is directly transmitted from the reservoir host to man.
32
What is metazoonosis?
infection is transmitted from the reservoir host to man via an arthropod.
33
What is saprozoonosis?
infection is transmitted via a non-animal developmental site as the soil and water.
34
What is studied in medical Parasitology?
Medical parasitology includes the study of 3 major groups of animals:
1. Parasitic helminths (worms).
2. Parasitic protozoa.
3. Arthropods directly cause disease or act as vectors of various pathogens
35
What is domestic zoonoses?
The source of infection is manβs own domesticated animals.
36
What are Protozoa?
These are unicellular organisms that occur singly or in colony formation. Each protozoan is a complete unit capable of performing all functions.
37
What is the morphology of Protozoa?
Protozoa have a wide range of sizes (1-150ΞΌ). The structure of a protozoan cell is formed of a cytoplasmic body and a nucleus.
38
What is the Cytoplasm of Protozoa formed of?
Ectoplasm and endoplasm
39
Ectoplasm of protozoa
Ectoplasm: The outer hyaline layer that is responsible for (REPSI) ingestion of food, excretion, respiration, protection, and sensation.
Some structures develop from ectoplasm as:
- Organs of locomotion; pseudopodia, flagella and cilia.
- Organs for food intake or excretion; peristome, cytostome, and cytepyge
40
Endoplasm of Protozoa
The inner granular part of the cytoplasm is responsible for nutrition and reproduction. The endoplasm contains a number of structures as food vacuoles, foreign bodies, contractile vacuoles, and chromatoid bodies and may contain RBCs.
41
Nucleus of protozoa
is the most important structure, as it regulates the various functions and reproduction. It is formed of:
a. Nuclear membrane.
b. Nuclear sap (nucleoplasm).
c. Chromatin granules.
d. Karyosome (nucleolus or endosome): It is a DNA-containing body, situated centrally or peripherally within the nucleus.
42
What are the parts of protozoa responsible for nutrition?
Endoplasm and ectoplasm
43
What are the parts of protozoa responsible for reproduction?
Entoplasm and nucleus
44
What is the protoplasm?
It is the cytoplasm + nucleus
45
Movement of protozoa
Protozoa may move by pseudopodia, cilia, and flagella with or without undulating (wavy) membrane.
46
Respiration of protozoa
It may be by direct taking of oxygen or by using oxygen liberated from metabolic processes (anaerobic).
47
Nutrition of protozoa
It is through:
a. Absorption of liquid food.
b. Ingestion of solid material through the ectoplasm by pseudopodia or the cytostome (mouth) and become surrounded by food vacuoles.
- Digestive enzymes take in the food and the undigested particles are forced out through the surface of the body or through a specialized opening (cytopyge - anal canal).
48
Excretion of protozoa
It is performed by osmotic pressure, contractile vacuoles, diffusion, or cytopyge.
49
Secretion of protozoa
A protozoan cell can secrete βCd chat PPβ cyst wall, digestive enzymes, pigments, proteolytic enzymes, hemolysins, cytolysins, toxic and antigenic substances.
50
Reproduction of protozoa
The parasite multiplies only in the trophozoite stage. The methods of reproduction are of the following types: Asexual, sexual
51
Asexual reproduction of protozoa
1. Simple binary fission: It is either longitudinal or transverse into two organisms.
2. Multiple fission (schizogony, merogony, or sporogony): In this process, the nucleus undergoes several successive divisions followed by the division of cytoplasm into small parts to produce a large number of small merozoites or sporozoites within the schizont, e.g. Plasmodium.
52
Sexual reproduction of protozoa
Gametogony or Syngamy: It means fusion of two cells one is female (macrogamete) and the other is the male cell (microgamete), e.g. Plasmodium.
53
What is the common type of reproduction in protozoa?
Asexual
54
Can plasmodium reproduce in two ways?
Yes, asexual and sexual
55
Transmission of protozoa
1. Simple life cycle: Intestinal and luminal protozoa require only one host, within which they multiply asexually, and transfer from one host to another directly.
2. Complex life cycle: Most blood and tissue parasites pass alternatively in a vertebrate and an invertebrate host, this is called alternation of generation (i.e. transmission is indirect). Sexual multiplication occurs in one host and asexual multiplication in another host.
56
Classification of protozoa Acc to the organ of locomotion.
1. Phylum: Sarcomastigophora (Amoebae and Flagellates):
a. Subphylum: Sarcodina (Amoebae): e.g. E.histolytica
b. Subphylum: Mastigophora (Flagellates): e.g. G.lamblia
2. Phylum: Ciliophora
3. Phylum: Apicomplexa e.g. Plasmodium falciparum (malignant malaria)
57
What are the general prevention ways of protozoa and control strategy?
```
ο· Environmental sanitation
ο· Health education
ο· Case treatment
ο· Pure water supply
ο· Safe and clean food
ο· Sanitary disposal of feces
ο· Insect control
```
58
What is the classification of arthropods?
Class insecta and class arachnida
59
What are the characteristics of class Insecta?
Body:
Wings:
Legs:
Head, thorax, abdomen
Present or absent
Three pairs (Hexapoda)
60
What are the characteristics of class Arachnida?
Body:
Wings:
Legs:
- Cephalothorax, abdomen - one mass
- Absent
- Four pairs (Octopoda)
61
What is the medical importance of arthropods?
1. Arthropods as disease agents:
- Dermatitis by the insect bite e.g., lice, mosquitoes.
- Inoculation of poisons e.g., ticks.
- Tissue invasion Sarcoptes scabiei (Scabies), larvae of flies (myiasis).
- Entomophobia: abnormal fear when seeing an arthropod (e.g., Spiders).
2. Arthropods as vectors for transmission of diseases agents, by:
- Mechanical transmission (Passive carrier), e.g. Typhoid fever by Musca fly.
- Biological transmission (Part of its Life cycle), e.g. Plague by Fleas
62
What are the general characters of mosquitos?
ο One pair of wings.
ο The female mouth is adapted for piercing & sucking of blood. Male feed on nectar.
ο Complete metamorphosis [Egg (on water surface) β> Larva (aquatic) β> Pupa (aquatic) β> Adult].
63
What is the medical importance of mosquitos? ( female transmits)
ο Human malaria (Anopheles spp.)
ο Lymphatic filariasis (Culex spp.) (elephantiasis is due to Normal mosquito)
ο Yellow fever, dengue fever (Aedes aegypti)
64
What are the methods of control of Mosquitos?
ο Physical control: Elimination of breeding places, bed nets, wire screening of doors and windows.
ο Biological control: Natural enemies such as frogs, Gambusia affinis fish.
ο Chemical control: Insecticides (Paris green as poison for larvae, DDT), repellants (Citronella oil).
65
What are the general characters of flies (Musca domestica)?
ο The adult fly is 6-10 mm long, grey in color. One pair of wings.
ο Mouth parts are soft, retractile, adapted for lapping and sucking fluids.
ο Complete metamorphosis [Egg (on ground) β> Larva β> Pupa β> Adult].
66
What is the medical importance of flies?
1. Mechanical transmission of Viruses, Bacterial & Parasites disease (e.g., protozoa cyst & helminths eggs).
2. Accidental myiasis.
67
What are the methods of control of flies?
ο Health education and sanitation.
ο Fly nets.
ο Insecticides e.g. DDT & Pyrethrum.
68
What are the general characters of lice (pediculus spp.)?
ο Small insect 2-4 mm, wingless. Permanent ectoparasites.
ο Mouth parts are adapted for piercing and sucking blood in all stages.
ο Incomplete metamorphosis [Egg β> Nymph β>Adult]
69
What are the names of lice infesting man?
ο Pediculus humanus capitis (head louse).
ο Pediculus humanus corporis (body louse).
ο Phthirus pubis (pubic louse): sexually transmitted parasite.
70
What is the medical importance of lice?
1. Head Lice (more common) cause itching and dermatitis (NOT known to transmit pathogens but stimulates its invasion).
2. Pediculosis (vagabondβs disease) by all types: severe dermatitis, skin becomes thickened hyper-pigmented skin.
3. Vector of diseases (body louse): as ο Epidemic typhus.
ο Epidemic relapsing fever. ο Trench fever.
71
What are the methods of treatment and control of lice?
ο Heath education and good hygiene. Frequent bathing.
ο Topical pediculicides (Permethrin lotion 1%, Benzyl alcohol).
ο Oral ivermectin.
ο Wet combing of hair (to remove eggs). Washing clothes and bed lining in boiled water
72
What are the general characters of fleas?
ο -Small, bilaterally compressed. Brown in color, with no wings.
ο -Mouth is adapted for piercing and sucking of blood.
ο - Complete metamorphosis (Egg β> Larva β> Pupa β> Adult).
73
What is the medical importance of fleas?
1- Plague:
- It is an acute severe bacterial disease.
- Fleas act as vectors and transmit them to humans;
- It is an acute infectious disease caused by bacteria (Yersinia pestis) which is transmitted from human or rats to human by fleas.
- e.g., Pulex irritans (Human flea), Xenopsylla cheopis (rat flea).
2- Endemic typhus feve (Rickettsial infection). Fleas act as vectors and transmit them to humans.
3- Flea dermatitis: Itching due to biting followed by a 2ry bacterial infection.
74
What are the methods of control of fleas?
1. Sanitation: Vacuuming of carpets and furniture.
2. Boiling of cloths and linings.
3. Application of insecticides as Pyrethrins or Insect growth regulators sprays for indoor and infested pets.
4. Flea traps
75
What are the general characters for ticks?
- The body is one mass sac-like.
- The mouth is adapted for piercing and sucking. (In all stages)
- Metamorphosis is gradual (Egg β> Larva (6L)β> Nymph (6L)β> Adult)
. - Ticks are classified into 2 families:
ο Ixodidae (hard ticks). ο Argasidae (soft ticks).
76
What is the Medical importance of ticks?
1. Diseases transmitted by ticks:
a) Bacterial diseases: e.g., Lyme disease.
b) Viral disease: e.g., Viral meningoencephalitis fever.
c) Protozoal diseases: e.g., Texas cattle fever.
2. It causes Dermatitis.
3. It causes Tick Paralysis.
- It is produced by some toxins in the saliva of the tick;
- it produces a blockage of the neuro-muscular junctions of the spinal cord. (When it is near the CNS)
- Paralysis disappears after the removal of the causative tick.
77
What is the treatment and control of tick paralysis?
- By the removal of the tick after covering the tick with ether or gasoline oil.
- Control: Spraying insecticides on the floors, in cracks in the walls
78
What are the important members of mites causing diseases to man?
1. Sarcoptes scabiei.
2. Demodex folliculorum.
3. House dust mites (HDMs).
79
What are the general characters of Sarcoptes scabies?
- It is a small mite (200-450 ΞΌm), grey (like flies) in color, oval in shape (itch mite).
β’ It has 4 pairs of legs as adult & nymph
and 3 pairs of legs as larva.
- Skin disease, worldwide, increase in poor hygiene & over-crowded areas.
- Mouth is adapted for tearing the tissues.
- Metamorphosis is gradual like lice and ticks (Egg Larva Nymph Adult).
80
What is the habitat of Sarcoptes scabiei and its life cycle?
ο Skin: It lives in intracutaneous tunnels of thin skin between fingers, wrist, back of the hands, elbows, axillae, breast, umbilicus, back, bends of the knee, groin, buttocks, and external genitalia.
ο The head and neck are not affected.
ο The female burrows tortuous tunnels in the skin epidermis and deposits eggs.
ο both larvae and nymph are found in hair follicles.
ο Maturity occurs after two weeks from the deposition of the eggs
ο The larvae and nymphs move freely over the skin and are found in hair follicles.
81
What is the mode of infection by Sarcoptes scabiei?
By contact with an infected person or contaminated clothes and sexual contact.
82
What are the clinical manifestations of scabies?
ο The activity of mites usually occurs at night. It is activated by the warmth of the affected part.
The characteristics are :
1. Mites produce tortuous tunnels, dark in color due to the toxins secreted and their excretions
2. Severe itching occurs that interfere with the sleep (insomnia)
3. Scratching and secondary bacterial infection occur on top, resulting in vesicles and pustules.
83
What is crusted scabies(Norwegian scabies)?
ο Crusted Scabies: (Norwegian Scabies):
- it is a severe form that can occur in immunosuppressed individuals.
- high numbers of mites are present in keratotic lesions all over the body.
- highly infective.
84
What is another name for scabies?
βseven years itchingβ
85
What is the diagnosis of scabies?
I. Clinically:
- history of severe itching during the night,
- its sites distribution in the skin,
- by finding the scratches, vesicles, and pustules.
II. Laboratory:
- skin scraping of intracutaneous tunnels or lesions
- rapid microscopic examination of the specimen by using Dermoscope.
86
What is the treatment of scabies?
1- Application of scabicidal:
- to the skin from the neck downwards,
- for 8-12 hours then washed. Repeated application is usually needed.
- Examples are:
ο Benzyl benzoate emulsion or cream (25%)
ο Pyrethrum cream 5%
ο Sulfur- lanoline suspension 5-10%
2- Ivermectin is given as a single oral dose, also as a topical application.
3- Frequent bathing.
4- Antihistaminic for itching. Antibiotics for secondary infection.
5- All members of the family must be treated.
87
What is the prevention and control of scabies?
1. Treatment of infected patients.
2. Boiling of internal clothes and bed linen.
3. Personal hygiene as frequent bathing.
4. Avoid contact with infected patients
88
What are the general characters of Demodex folliculorum?
It is the hair follicle mite. It is very minute and elongated.
89
What is the habitat of demodex folliculorum?
- It lives in the hair follicles and sebaceous glands particularly of the face around the nose, eyelids, and mouth.
90
What is the mode of infection of Demodex folliculorum?
- It is transmitted by direct contact with the patient or by using polluted towels.
91
What are the clinical manifestations of Demodex follicolurum?
- It causes :
ο acne, blackheads
ο dermatitis and blepharitis.
92
How is Demodex follicolurum diagnosed?
Squeeze out the contents of the blackhead or sebaceous gland and examine under the microscope for the adult and its stages.
93
What is the treatment of Demodex follicolurum?
- Sulphur ointment 15% or Benzyl benzoate 25%.
| - Oral Ivermectin (like lice)
94
What are house dust mites?
- These are found in dust on the floors, furniture, mattresses, and beds.
- House dust mites contain allergens that produce allergic reactions in humans.
95
What are the clinical manifestations of house dust mites?
They cause :
ο allergic rhinitis,
ο conjunctivitis,
ο dermatitis and bronchial asthma.
96
What is the prevention and control of house dust mites?
1. Exclusion of dust from bedrooms and furniture of sensitive individuals.
2. Cleaning of carpets, beds, and furniture using a vacuum cleaner
97
What is the definition of Myiasis?
It is the invasion of the tissues of man or animals by larvae of dipterous (have 2 wings) flies.
98
What is Myiasis classified according to?
- According to the habitat (site of invasion)
| - According to the habit (biological habit of the fly)
99
What are the types of Myiasis according to the habitat?
Internal: intestinal and urogenital
External: cutaneous, ocular, nasopharyngeal, and aural
100
How does intestinal Myiasis occur?
Flies may deposit their eggs or larvae on human food or on the anus (particularly in children in rural areas) during sleep or defecation in open places.
101
What are the symptoms of intestinal myiasis?
Larvae find their way to the intestine and cause non-specific symptoms like nausea, vomiting, abdominal discomfort, or pain with diarrhea.
102
Where can we find larvae in case of intestinal myiasis?
Living and dead larvae appear in stools or vomitus
103
What are examples of larvae that cause intestinal myiasis?
larvae of Calliphora, Lucilia, Musca, and Fannia.
104
How does urogenital myiasis take place?
Larvae may enter through urinary or genital orifices or through lesions on orifices during urination in open places.
105
What are the symptoms of urogenital myiasis?
They may cause obstruction to the urine flow with dysuria or inflammation in the urinary passage with pus, mucus, and blood in the urine.
106
Where can we find the larvae in case of urogenital myiasis?
Larvae are passed in the urine.
107
What are examples of larvae that cause urogenital myiasis?
Fannia (the latrine fly) , Musca, Calliphora and Sarcophaga
108
How does cutenous myaisis take place?
- This occurs when wounds or ulcers are invaded by larvae of the flies.
- Sometimes, larvae may invade intact skin causing boil-like lesions.
109
What are the symptoms of cutaneous myiasis?
C/P: Sever pruritis, creeping eruption, or boil-like lesion may be presenting symptoms.
110
What are examples of larvae that can cause cutaneous myiasis?
Example: . Wohlfahrtia, Chrysomia ,Cordylobia and Dermatobia.
111
How do ocular or nasopharyngeal myiasis take place?
Larvae of some flies are attracted to the discharge coming from the eye or the nose, to find their way to the conjunctiva or the nose and may sometimes reach the brain.
112
What are the symptoms of ocular or nasopharyngeal myiasis?
- Severe pain in the eye is the first complaint in ocular myiasis followed by lacrimation and conjunctival irritation.
- c/p: Nasal myiasis presented with foul-smelling discharge followed by nasal obstruction, fascial oedema, frontal headache, and epistaxis.
113
What are examples of larvae that can cause ocular or nasopharyngeal myaisis?
Calliphora, Sarcophaga, and Hypoderma
114
How can aural myiasis take place?
- Purulent exudates discharged from running ears attract some flies and they lay eggs or larvae there.
- Larvae invade the middle ear, inner ear, or brain tissue in extreme cases.
115
What are the symptoms of aural myiasis?
C/P: Patient complains of crawling sensation and buzzing noise and sometimes foul-smelling discharge or perforation of the drum occur.
116
What are examples of larvae that can cause aural myiasis?
Cochliomyia, Wohlfahrtia, Sarcophaga, Lucilia and Chrysomia.
117
What is myiasis classified into according to the biological habit of the fly?
Specific, Non-specific and accidental
118
What is specific myiasis?
This is the condition when larvae invade only living tissues (Obligatory tissue parasites)
119
What are examples of specific myiasis?
- Hypoderma and Dermatobia: the larvae of which, invade the skin causing boil-like swellings
- Wohlfahrtia and Oestrus: invade the eyes, nose, and external ears
120
What are the sites of specific myiasis and its symptoms at each place?
ο In the eye, they cause conjunctivitis and corneal ulcers.
ο In the nose, obstruction and persistent bloody purulent discharge.
ο In the ears, external otitis.
121
What is the definition of semi-specific myiasis?
includes flies that habitually oviposit or larviposit on dead tissues of man or animals or decaying organic matter (Facultative parasites), However, they can be attracted by the offensive discharge coming from neglected wounds, or inflamed ears and eyes and thus deposit their larvae or eggs in such tissues.
122
What does the presence of larva do in case of non-specific Myiasis?
The presence of larvae prevents healing and induces sepsis.
123
What are examples of semi-specific myiasis?
Sarcophaga, Lucilia, Calliphora, Wohlfahrtia and Chrysomia.
124
What is accidental myiasis?
- When the fly eggs or larvae are deposited on food material (e.g. cheese and vegetables) and then they are accidentally ingested leading to intestinal myiasis.
- Also, when the eggs are deposited around the anal canal or urogenital orifice, the larvae can travel up the passages leading to intestinal or urogenital myiasis, respectively.
125
What are examples of larvae that cause accidental myiasis?
Biophilia in cheese, Drosophila in fruits, and Fannia (the latrine fly).
126
How is myiasis diagnosed?
(1) Clinical picture according to the tissue invaded.
| (2) By finding the larvae in the lesion.
127
How are larvae identified?
Larvae are identified by their posterior spiracles or through their breeding to become adult
128
What are the methods of treatment of myiasis?
1- Removal of the larvae:
ο manual excision or endoscopy
ο by using purgatives or douches
ο following suffocation of larvae by Vaseline or petroleum oil
2- Treatment of secondary infection by antiseptics and antibiotics.
129
What are the methods of prevention and control of myiasis?
1. Insecticides and nets for the control of flies.
2. Protection of food from flies by following strict hygienic measures.
3. Cleaning and covering of wounds by gauze and wound dressing
130
What is the benefit of larvae of flies?
(1) The flies' larvae represent an important food source for many living organisms as birds and lizards.
(2) Some people in different cultures depend on these larvae as a food source rich in protein.
(3) Maggot therapy
131
What is maggot therapy?
the medical usage of flies' larvae):
ο It is a type of old used traditional therapy involving the introduction of life, disinfected fly larvae into non-healing skin and soft tissue wounds of a human for the purpose of cleaning out the necrotic tissue within a wound (debridement) and disinfection and enhancing healing.
ο Select a species that feeds almost exclusively on necrotic tissue
132
What does helminth mean?
Helminth is a general term meaning worm.
133
What are helminths classified into?
Helminths are classified into flatworms or platyhelminths (trematodes and cestodes) and nemathelminths (nematodes).
134
What are the general characters of trematodes?
1) Dorsoventrally flattened (Schistosoma females are cylindrical), leaf-shaped, bilaterally symmetrical.
2) Possess an oral sucker around the mouth and a ventral sucker (for fixation).
3) A well-developed alimentary canal with a muscular pharynx, esophagus, and a branched intestine.
4) Body cavity is lacking.
5) Hermaphroditic; having both male and female reproductive organs in the same adult (except schistosomes).
135
What are the general characters of schistosomes?
ο Belong to trematodes.
ο Have separate sex.
ο Females are cylindrical.
136
What are the general characters for cestodes?
- Flattened, elongated, segmented.
- Body is divided into:
ο² A scolex or head bears the organs of attachment (acetabula, rostellum, hooks).
ο² A neck: the region of segment proliferation.
ο² A chain of proglottids called the strobila:
β’ The strobila elongates as new proglottids (segments) form in the neck region.
β’ The segments nearest the neck are immature (sex organs not fully developed)
and those more posterior are mature.
β’ The terminal segments are gravid, with the egg-filled uterus as the most prominent feature.
ο Absent alimentary canal.
ο Hermaphroditic.
137
What are the general characters for nematodes?
ο Cylindrical rather than flattened.
ο Complete alimentary canal
ο² Mouth: surrounded by lips bearing sensory papillae, in some species is provided with teeth. It leads into a buccal cavity
ο² Esophagus: a muscular structure that pumps food into the intestine.
ο² Intestine: a tubular structure that ends with the anus. ο Have separate sex, males are usually smaller than females.
138
What are the modes of transmission of helminth infections?
1) Ingestion of contaminated water or food.
2) Ingestion of infected fish or infected meat.
3) Inhalation to the nasopharynx.
4) Skin penetration.
5) Arthropod bite.
6) Contact with domestic animals, such as dogs.
7) Infected persons may be direct sources of infection.
139
What are the clinical presentations of helminth infections?
1) Gastrointestinal affection: abdominal pain, nausea, vomiting, diarrhoea, dysentery, or constipation.
2) Lung affection: chest pain, fever, cough, pneumonia, or haemoptysis.
3) Liver affection: biliary colic, jaundice, fever, or right hypochondrial pain.
4) Loss of weight, anaemia, vitamin deficiency.
5) Complications: intestinal obstruction, haematemesis, melena, or cancer.
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How are helminths diagnosed?
ο Clinical.
ο Laboratory:
ο² Macroscopic and Microscopic examination of stool for ova, gravid segments, adults, or larvae.
ο² Other samples that can be used to diagnose helminth infections include duodenal aspirate, urine, sputum, or blood.
ο² Immunological: ELISA, IHAT.
ο² Molecular: PCR.
ο Radiological: X-ray, US, CT, MRI.
ο Endoscopy: e.g. cystoscopy or sigmoidoscopy.
ο Histopathological diagnosis: e.g. muscle biopsy.
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What are the general preventive and control measures for helminth infection?
1) Thorough washing of vegetables and fruits.
2) Provision of safe water supply.
3) Proper cooking of meat (beef or pork).
4) Proper cooking of fish.
5) Snail control.
6) Anti-fly and anti-mosquito measures.
7) Destruction of reservoir hosts (e.g. rodents).
8) Periodic examination and deworming of pets.
9) Treatment of infected cases or animals.
10) Health education: mode(s) of transmission, and prevention and control measures.
11) Environmental sanitation: sanitary disposal of feces.
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What are the diagnostic samples for helminths?
```
ο² Stool.
ο² Duodenal aspirate.
ο² Urine.
ο² Sputum.
ο² Blood.
```
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What is the habitat of trematodes?
Small intestine, biliary passages, blood vessels
144
What is the habitat of cestodes?
Small intestine, tissues
145
What is the habitat of nematodes?
Small or large intestine, tissue
146
Eggs of trematodes
- Operculated; has a lid (Schistosoma eggs are non- operculated)
- Mature (contains miracidium) or immature
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Eggs of cestodes
- Most of them have non- operculated eggs
| - Mature (contains hexacanth embryo or oncosphere)
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Eggs of nematodes
ο Non-operculated
ο Mature (contains completely formed larva) or immature
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Eggs of trematodes pass to?
Fresh or brackish water
150
Eggs of cestodes pass to?
- Most of them need soil to complete their life cycle
- Tapeworms shed gravid proglottids into the intestine.
- Some proglottids disintegrate, releasing eggs that are voided in the feces, other proglottids are passed intact
151
Eggs of nematodes pass to?
Soil
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What are the stages of the life cycle of helminths?
- Egg β larva(e) (in intermediate host) β adult (in the definitive host)
- Some nematodes produce larvae instead of eggs
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What are the larval stages of trematodes?
MSR CE
```
ο Miracidium
ο Sporocyst
ο Redia
ο Cercaria
ο Encysted metacercaria
ο (Schistosomes have no redia)
```
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What are the larval stages of cestodes?
ο Cysticercus larva ο Cysticercoid larva ο Hydatid larva
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What are the stages of larvae of nematodes?
ο Rhabditiform larva
| ο Filariform larva (Each larval stage is followed by a molt)
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Which type of helminth needs a snail as an intermediate host?
Trematodes
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What are the hosts of trematodes?
Two
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What is the number of hosts of cestodes?
Two hosts (except Hymenolepis nana)
159
What is the number of hosts of nematodes?
Some need an arthropod vector or animal host, while others develop with no IH.
