Parasitology Notes

Introduction to Parasitology

• Deals with organisms residing on/within other organisms to procure food and their relationship to hosts.

• Parasite: Organism living in/on another for survival.

• Host: Organism a parasite depends on for survival.

Types of Parasites

• Nemathelminthes (Roundworm)

  • Nematodes (Ascaris, Trichuris, Hookworm)

• Platyhelminthes (Flatworm)

  • Cestodes (Tapeworm)

  • Trematodes (Liver flukes, Blood flukes, Intestinal flukes, Lung flukes)

• Protozoa

  • Amoeba

  • Malaria

Effects of Parasites on Hosts

• Pathogenic: Produces disease pattern, causes infection.

• Non-pathogenic: Does not produce disease pattern.

Types of Association of Living Organisms

• Symbiosis: Relationship where one organism cannot live independently.

• Mutualism: Both organisms benefit.

• Commensalism: One organism benefits, the other is not harmed.

• Parasitism: One organism benefits, the other is harmed.

Special Types of Parasites

• Ectoparasites: Live outside the body of the host.

• Endoparasites: Live within the body of the host.

• Incidental Parasites: Establish in an unusual host.

• Temporary Parasites: Free-living part-time, seek hosts for nourishment.

• Permanent Parasites: Live on/in host from early life to maturity.

Types of Hosts

• Definitive Host: Harbors adult or sexual stages of parasite.

• Intermediate Host: Harbors asexual or larval stage.

• Paratenic Host: Harbors parasite in arrested development/infective stage.

• Dead-end Host: Parasite transmission cycle cannot continue.

• Reservoir Host: Animals harboring the same parasites.

Major Methods of Transmission of Parasites to Man

• Digestive system: Ingestion of contaminated food, milk, water.

• Through the skin.

• Reproductive system.

• Respiratory tract.

• Placenta.

• Contact with animals.

Mode of Ingestion

• Ingestion

• Penetration: Skin, sexual contact

• Vector: Mosquitos

Entry of Parasites (Infective Stage)

• Oral: Ingestion of infective stage (cyst and embryonated egg)

  • Embryonated egg of Ascaris lumbricoides

  • Protozoan cyst

  • Intimate oral contact: T. tenax, E. gingivalis

• Skin: Acute larval penetration

  • Filariform (hookworm)

  • Cercaria (schistosomes)

  • Arthropod-vector transmitted: Malaria, Leishmania, Trypanosomes

• Sexual intimacy: T. vaginalis, Histolytica, G. lamblia

• Intranasal (sinuses to the brain)

• Airborne (inhalation)

Exit of Parasites (Diagnostic Stage)

• Urine

• Stool

• Sputum: Amoebic abscess (P. westermanii)

• Blood: Malaria, Filaria

• Tissue biopsy

  • Muscle

  • Rectal

  • Lymph gland

  • Skin biopsy

• Tissue aspirate

  • Liver

  • Duodenal

  • Broncho-alveolar lavage/lung washing: Pneumocystis

• Orifice swab

  • Vaginal

  • Peri-anal

Prevention

• Reduction of sources of infection via therapeutic measures.

• Education in personal prophylaxis.

• Sanitary control of water, food, work conditions.

• Destruction/control of reservoir hosts and vectors.

Nematoda (True Roundworm)

• Elongated, cylindrical, not segmented, separate sexes, complete digestion, chemoreceptors.

• Classified by presence/absence of caudal receptors.

  • Without phasmids (trichiura, trichinella, capillaria)

  • With phasmids (all nematodes except trichiura, capillaria, trichinella)

Habitat

• Intestinal

  • Small intestine: Ascaris, hookworm, strongyloides, capillaria (heart and lung journey phase)

  • Large intestine: Trichuris, enterobius (no heart and lung journey phase)

  • Eggs: Ascaris, trichuris, enterobius

  • Filariform: Hookworm, strongyloides

• Extra-intestinal

  • Lymph: Filarial (Bancrofti and Malayi)

  • Muscles: Trichenella

  • Meninges: Angiostrongylus cantonensis

Nemanthelminthes (Roundworm) General Characteristics

• Females larger than males with straight tail.

• Males have curved tail with spicule for copulation.

• Unsegmented.

• Round, elongated, few millimeters in length.

• Found in intestine, blood, and tissue.

Classification of Nematodes

• Presence/Absence of caudal receptors

  • Phasmid nematodes

  • Aphasmid nematodes

• Habitat

  • Intestinal nematodes (SI and LI)

  • Extraintestinal nematodes (tissue)

• Infective stage of intestinal nematodes

  • Eggs (ova)

  • Filariform

• Infective stage of extraintestinal nematodes

  • Filarial worm

  • Muscles

  • Meninges

Ascaris Lumbricoides

• Common Name: GIRI

• Disease: Ascariasis, Ascaris infection, Roundworm infection

• Morphology

  • Worms: Largest nematodes, no intermediate host, smooth cuticle, conical extremities, terminal mouth with 3 oval lips with sensory papillae

• Eggs: measure 45 – 70 u, there is an outer coarsely mamillated. Egg proper has a thick, transparent, hyaline shell. Typical fertile eggs measure 88 – 94 u x 39 – 44 u, have a thinner shell with an irregular coating of albumin

• Epidemiology: Most prevalent in 5-9 year olds, transmitted hand-to-mouth via contaminated soil.

• Pathology and Symptomatology

  • Larval migration may cause host sensitization, allergic manifestations, pulmonary infiltration, asthmatic attacks, edema of the lips.

  • Loeffler’s Syndrome: Eosinophils accumulate in lungs due to parasitic infection causing lung clinical manifestations, due to migration of larvae; diagnosis is made by finding eggs in feces.
    Piperazine citrate is safe and effective.

• Obstruction of Ascaris

  • Intestinal itself – bolus

  • Pharyngeal – suffocation of the patient, which causes vomiting and abdominal pain

  • Common bile ducts – formation of a gallstone

• Most common complaint: vague abdominal pain.

Enterobius Vermicularis

• Common Name: Pinworm, Seathworm, Dormitory worm, Society worm

• Disease: Enterobiasis, Oxyuriasis

• Habitat: Cecum / Large intestine

• Morphology

  • Males and females possess alae (longitudinal cuticular ridges) which aid in identification. Adult has cephalic alae

  • Small adult female worm has cuticular alar expansion, prominent esophageal bulb, long pointed tail.

  • Size: male 2-5 mm; Female 8-13 mm

  • Uteri of the gravid females are distended with eggs

• Epidemiology

  • Infection via hand-to-mouth transmission, contaminated fomites, inhalation of airborne eggs, retroinfection through anus.

  • "The largest number of eggs was found in bedrooms."

• Diagnosis:

  • Demonstrating eggs on scotch tape slide or cellophane anal swab taken from the peri-anal skin in the morning on waking.

  • Egg resembles the letter D.

  • Eggs should not be found in a fecal specimen unless it encounters the peri-anal skin.

Trichuris Trichiura

• Common Name: Whipworm

• Disease: Trichuriasis, Trichocephaliasis, Trichocephalus dispar, Trichocephalus trichiura

• Epidemiology: Highest incidence in heavy rainfall regions, subtropical climate, polluted soil.

• Morphology

  • Worm: Parallel prevalence of ascaris, adult posterior end is very thin. Attenuated whip-like structure, more robust posterior. Similarity in length: male 30-45 mm; female 35-55 mm male – with thin anterior end, posteriorly straight; female – posterior end is curved/coiled about 36’

  • Egg: Lemon-shaped with plug-like translucent polar prominences.Egg barrel-shaped, Japanese lantern egg, football shape, golden brown. Sometimes the egg appears bizarre due to therapy

• Lives in human cecum, appendix, lower ileum. Dislikes overcrowded environments. Some migrate to rectosigmoid colon.

• Heavy chronic infections:

  • Frequent, small, blood-streaked diarrheal stool

  • Abdominal pain and tenderness

  • Anemia

  • Rectal prolapse (borborygoni)

• Prevention

  • Treatment of infected individuals

  • Sanitary disposal of human feces

  • Instruction of children in sanitation and personal hygiene

  • Thorough washing/scalding of uncooked vegetables

• Diagnosis: Direct Fecal Smear (DFS) finding lemon-shaped eggs in feces.

  • Trichuris vulpis – trichuris of dogs

  • Trichuris muris – trichuris of mouse

  • Trichuris suis – trichuris of pig

Strongyloides Vermicularis

• Common Name: Threadworm

• Disease: Cochin-china diarrhea Vietnam diarrhea

• Habitat: Small intestine (duodenum)

• Morphology

  • Worm: Adults - Smallest nematodes, long cylindrical esophagus, lacks posterior bulb. Rhabditiform larva (non-infective) - 250 um long, muscular esophagus (club-shaped anterior). Short buccal cavity, prominent primordial genitalia. Filariform larvae (infective) - 600 um long, lack of bulb on esophagus, notch at end of tail

  • Facultative parasites: Can produce free-living adult males and females

  • Female parasite is parthenogenesis (self-fertilization).

• Egg: Compared to HW, strongyloides is thin with segmented germ cells

• Autoinfection: occurs when patient has fever, constipation, poor hygiene.

• Signs and Symptoms: Itchiness, nausea, vomiting, intestinal obstruction, diarrhea, weight loss.

• Mode of Transmission: Skin penetration

• Diagnosis: Harada Mori, Baerman Culture

Hookworm

• Two Main Groups of Hookworm

  • Human Hookworm

    • Necator Americanus

      • CN: New World Hookworm, The American Murderer

      • Often found in the jejenum

      • Copulatory spicule: barbed

      • Dorsal ray: bidigitate / bipartite

      • Blood consumed: 0 – 0.3 ml/day

      • Buccal Capsule: dorsal pair of semilunar cutting plates and concave dorsal medium tooth

    • Ancylostoma Doudenale

      • CN: Old World Hookworm

      • Often found in the duodenum

      • Copulatory spicule: simple

      • Dorsal ray: trigiditate

      • Blood consumed: 0.15 – 0.26 ml/day

      • Buccal Capsule: 2 ventral pairs of teeth

  • Animal Hookworm

    • Ancylostoma Brazilienze

      • CN: Cat Hookworm

      • Buccal Capsule: 2 ventral pairs of teeth

    • Ancylostoma Caninum

      • CN: Dog Hookworm

      • Buccal Capsule: 3 pairs of ventral teeth

• Habitat: Small intestine

• Disease: Ancylostosomiasis, Necatoriasis, Miner’s disease

• Morphology:

  • Worm: Male hookworm – presence of fanlike expansion. Female hookworm – has a straight posterior end. Adults - Male 8-11mm long; possesses a bursa which aids in speciation of hookworm

  • Female 10-13 mm long

  • Rarely seen in stool since rigidly attached to mucosa. Infective stage (Filariform larvae) - 700 um long

  • Straight esophagus, pointed tail, long buccal cavity. Rhabditiform larvae - 250 um long

  • Bulbous esophagus, long buccal cavity

• Egg: Eggs of Necator and Ancylostoma look alike, ovoidal, slightly smaller than an ascaris egg, has a very thin eggshell – inside the eggshell (ovum), there is a germ cell in fragmentation (2-8 germ cells).

• Pathology: Pneumonitis, allergic reaction (dermatitis) "ground itch", alveolar hemorrhage, microcytic hypochromic anemia – adults have buccal cavity, able to suck blood, constant blood loss so there is an anemia.

Trichinella Spiralis

• Common Name: Trichina worm, Tissue Roundworm, Garbage worm

• Disease: Trichinosis, not in the Philippines. Zoonotic.

• Infective Stage: Ingestion of encysted larvae in undercooked pork. Larva encysted in skeletal muscle.

• Definitive Host: Adult

• Intermediate Host: Larval

• Requires 2 hosts to complete cycle. In man, it's a blind alley infection, needs 2nd host for transmission.

• Morphology

  • male 1.5mm long, no copulatory spicule

  • female 3mm long

  • larvae encysted in skeletal muscle

  • Male has a posterior end and has a pair of conical papillae

  • female – larviparous

• Muscles Affected: Muscle of respiration (diaphragm, intercostal muscle), muscle of the heart, muscles of the arm (biceps and triceps), muscle of the eye (peri-orbital area), muscle of the tongue (masseter)

• Signs and Symptoms: Orbital edema, muscle pain, eosinophilia

• Pathology: Inflammation, granuloma formation, calcification, prognosis depends on affected muscles.

• Diagnosis

  • muscle biopsy – best test, but with limitations

  • serology CFT – complement fixation test BFT – benzonite flocculation test in vitro ELISA Bachman Intradermal Test – in vivo

  • animal inoculation

Capillaria Philippinensis

• Causative agent of a mystery disease

• Common Name: Pudok’s worm

• Intermediate Host: Fish (glass fish)

• Morphology

  • Worm: Adults are threadlike. Male has posterior chitinous spicules

  • Female: Typical (1 row of eggs in uterus), Atypical (2-3 rows of eggs in uterus)

  • Egg: Typical egg - eggshells are striated, have a flat bipolar plug. atypical egg – peanut-shaped

• Pathology: Malabsorption syndrome, borborygoni, abdominal pain, diarrhea.

Blood and Tissue Nematodes: Wuchereria Bancrofti

• Habitat: Lymphatic System

• Disease: Filariasis and Elephantiasis

• Transmit disease: Dengue

• Intermediate Host: Mosquito (Aedes Minimus Flavirostrie)

• Two terms: Arthropod-Borne Tropical Parasite Disease Vector-Borne Tropical Parasite Disease

• General Characteristic: Requires an arthropod as an intermediate host; when an infected arthropod takes a blood meal, the microfilariae are released into a human host.

Microfilaria

• exhibit periodicity (rhythmical appearance) – it is important in knowing the best time to collect blood

  • periodic – only during night (nocturnal) or only during day (diurnal)

  • sub-periodic – day and night with increased concentration at night

  • non-periodic – the number of microfilariae remains constant at day and night
    Microfilariae Classification:

• Sheathed (Bancrofti, Malayi and Loaloa) - The larva is covered in a thin, delicate membrane

• Unsheathed (Volvulus, Pustans, Ozzandi) - the larva is bare/naked

Brugia Malayi Co-Exists With Wuchereria Bancrofti

Wucheriria Bancrofti

• not only found in blood but also in urine, which is chyluric

• found in the gut, because they are found in the lower lymph node

• cause bancroftian filariasis (lower extremities)

Brugia Malayi

• cause Malaysian filariasis (upper extremities)

• Elephantiasis – an enlargement of some organs secondary to a block in lymphatic flow

• Organs usually affected:

  • limbs

  • scrotum

  • breast

  • labia majora

Loaloa

• African eyeworm

• Causes: loaisis, fugitive swelling or Calabar swellings – allergic reaction to worm migration to tissue in death in capillaries

• Onchocerca Volvulus

• Blinding worm, Gale filarienne, craw-craw

• Causative agent of river blindness

• Disease: robles disease, onchocerciasis

• Major symptoms:

  • Destruction of blood cells and hemoglobin

  • Elephantiasis – enlargement of the lower extremities

  • Enlargement of the liver and spleen

• Diagnosis

  • finger prick blood

    • counting chamber

    • thick stained smear

    • capillet method

  • concentration venous blood

    • knott’s method