PARASITOLOGY

• Nematodes, also known as "round worms," are unsegmented with elongated cylindrical bodies
• The body of nematodes is covered by a thick hyaline protective covering called "cuticula"
• Nematodes have a complete set of digestive system equipped with a mouth and an anus
• Nematodes have separate sexes and sensory organs/chemoreceptors
• Sensory organs in nematodes include:

  • Amphids: paired sensory organs located at the level of cephalic papillae found in all nematodes (cephalic)
  • Phasmids: paired structures found posteriorly (caudal)
• Nematodes can be homoxenous or heteroxenous
• Ways of acquiring roundworm infection:

  1. Ingestion of fully embryonated egg

  2. Ingestion of encysted larva

  3. Larval skin penetration

  4. Through bites of arthropods vectors/skin inoculation
• Classification of roundworms:

  1. According to Life Stages:

  • Oviparous: female roundworms capable of producing eggs without fully developed larva in its shell
  • Ovoviparous/oviviparous: female roundworms capable of producing eggs with fully developed larva in its shell
  • Viviparous/larviparous: female roundworms that do not produce eggs but instead deliver fully developed larva

  2. According to Habitat:

  • Intestinal:
  • Small Intestine: Capillaria philippinensis, Ascaris lumbricoides, Strongyloides stercoralis, Hookworms
  • Large Intestine: Trichuris trichiura, Enterobius vermicularis
• • Extra Intestinal: Brugia malayi, Loa loa, Onchocerca volvulus, Wuchereria bancrofti, Mansonella ozzardi, Acanthocheilonema perstan/Dipetalonema perstan, Dracunculus medinensis
• Classification according to the presence or absence of caudal chemoreceptors:

  • Phasmidea/Sercenentea: those with caudal chemoreceptors
  • Aphasmidea/Adenophorea: those without caudal chemoreceptors
• Species:

  • Ascaris lumbricoides
  • Trichuris trichiura
  • Enterobius vermicularis

  Common Name:

  • Giant Intestinal Round Worm
  • Whipworm
  • Pinworm/seat worm/society worm
• Life Cycle of Ascaris lumbricoides:

  1. Adult female produces fertilized and unfertilized eggs passed out in feces

  2. Fertilized eggs embryonate on soil

  3. Larva hatches in the small intestine, penetrates the intestinal wall, and starts its Pulmonary Migration

  4. Larva matures into an adult in the small intestine
• Morphology of Ascaris lumbricoides:

  • Ova/Egg: Fertilized and unfertilized eggs with specific measurements and characteristics
  • Adult worms: Pink or white, with specific measurements and features resembling an earthworm
• Disease caused by Ascaris lumbricoides:

  • Infections can be asymptomatic or show light symptoms like abdominal discomfort
  • Heavy infections can cause intestinal blockage and impair growth in children
  • Treatable with medication prescribed by a healthcare provider
• Prevention & Control of Ascaris lumbricoides:

  1. Avoid ingesting contaminated soil

  2. Wash hands before handling food

  3. Teach children the importance of handwashing

  4. Wash, peel, or cook raw vegetables and fruits before eating

  5. Treatment with anthelminthic medications like albendazole and mebendazole
• Life Cycle of Capillaria philippinensis:

  • Common Name: Pudoc Worm
  • Habitat: Small intestine
  • Infective stage: Embryonated egg
  • Mode of Transmission: Ingestion of inadequately cooked small freshwater/brackish water fishes
• Morphology of Capillaria philippinensis:

  • Ova/Egg: Similar to Trichuris but smaller, with specific measurements and characteristics
  • Adult worms: Specific measurements and features of male and female worms
• Disease caused by Capillaria philippinensis:

  • Symptoms include abdominal pain, diarrhea, nausea, vomiting, weight loss, and potential death
  • Prevention through proper hygiene and disposal of fecal matter
• Prevention & Control of Capillaria philippinensis:

  1. Use specific latrines to prevent contamination

  2. Wash hands after touching soil and before handling food

  3. Teach children the importance of handwashing

  4. Wash fruits and vegetables before eating

  5. Avoid eating raw or undercooked fish

  • Treatment with medications like mebendazole and albendazole
• Life Cycle of Trichuris trichiura:

  1. Adult female produces eggs passed out in feces, which embryonate on soil

  2. Embryonated egg ingested by man

  3. Larva hatches in the small intestine and matures into an adult in the cecum
• Morphology of Trichuris trichiura:

  • Ova/Egg: Specific measurements and characteristics
  • Adult worms: Features of male and female worms
• • Adult male is 30 - 45 mm long and with coiled posterior end
• Morphology of Trichuris trichiura:

  • Egg measures 50 - 54 um x 23 um
  • Eggs are barrel shaped/ football shaped/ lemon or lantern shaped with polar prominences
  • Egg has a yellowish outer and a transparent inner shell
  • Commonly referred to as “Japanese Lantern Ova”
  • Eggs more susceptible to dessication than those of Ascaris eggs
  • Adult worms are pinkish gray in color
  • Anterior 2/3 of the worm is slender giving it a whip like appearance
  • Adult males are slightly shorter than females
  • Adult female is 35 - 50 mm long and with bluntly rounded posterior end
• Disease caused by Trichuris trichiura:

  • People infected can suffer light or heavy infections
  • Light infections usually have no symptoms
  • Heavy infections can lead to frequent, painful passage of stool containing mucus, water, and blood
  • Rectal prolapse can occur
  • Heavy infection in children can lead to severe anemia, growth retardation, and impaired cognitive development
  • Treatable with medication prescribed by a health care provider
• Diagnosis of Trichuris trichiura:

  • Standard method is by microscopically identifying whipworm eggs in a stool sample
  • A concentration procedure is recommended for light infections
• Treatment for Trichuris trichiura:

  • Anthelminthic medications such as albendazole and mebendazole are the drugs of choice
  • Infections are generally treated for 3 days
  • Health care providers may repeat a stool exam after treatment
  • Iron supplements may be prescribed if the infected person suffers from anemia
• Prevention & Control of Trichuris trichiura:

  • Avoid ingesting soil contaminated with human feces
  • Wash hands with soap and warm water before handling food
  • Teach children the importance of washing hands
  • Wash, peel, or cook all raw vegetables and fruits before eating
• Life Cycle of Trichuris trichiura:

  • Adult female produces eggs in the large intestine
  • Eggs are laid in the anal region
  • Eggs become infective within 4 - 6 hours
  • Embryonated egg ingested by man
  • Larva hatches in the small intestine
  • Larva goes to the cecum and matures into an adult
• Morphology of Enterobius vermicularis:

  • Egg measures 50 - 60 um x 20 - 30 um
  • Eggs are ovoid with one side flattened
  • Shell is transparent with 2 layers and occasionally motile embryo
  • Adult worms are whitist in color with cuticular alar expansion at the anterior end and a prominent esophageal bulb
  • Adult female is 3 - 8 mm x 0.4 mm long with a pointed tail end
  • Adult male is 2 - 5 mm x 0.1 – 0.2 mm with curved tail
• Disease caused by Enterobius vermicularis:

  • Common clinical manifestation is an itchy anal region
  • Heavy infection can lead to secondary bacterial infection
  • Symptoms include teeth grinding, insomnia, abdominal pain, and appendicitis
  • Infection of the female genital tract has been reported
  • Diagnosis can be reached through simple techniques
• Prevention & Control of Enterobius vermicularis:

  • Wash hands with soap and warm water after using the toilet and before handling food
  • Infected individuals should bathe every morning to remove eggs on the skin
  • Avoid co-bathing with others during infection
  • Comply with good hygiene practices such as regular handwashing and nail care
• Treatment for Enterobius vermicularis:

  • Medications used are mebendazole, pyrantel pamoate, and albendazole
  • Given in 1 dose initially and another single dose 2 weeks later
  • Health risks and benefits should be considered for patients under 2 years of age
  • Repeated infections should be treated similarly to the first infection
• Common organisms detected on stool examination and potential pathogenesis:

  • Ascaris lumbricoides
  • Hookworm
  • Trichuris trichiura
  • Strongyloides stercoralis
  • Tapeworm
  • Ophisthorchis spp.
  • Fasciola spp.
  • Schistosoma
  • Toxocara spp.
  • Entamoeba histolytica
  • Cryptosporidium spp.
  • Giardia intestinalis
• • Trichinella spiralis
• Causes of eosinophilia:

  • Eosinophilic syndrome
  • Pemphigoid
  • Pemphigus
  • Polyarteritis nodosa
  • Arboviral infections
  • Brucellosis
  • Enteric fever
  • Leishmaniasis
  • Leprosy
  • Malaria
  • Trypanosomiasis
  • Tuberculosis
  • Angiostrongylus
  • Anasaciasis
  • Capillaria spp.
  • Cysticercosis (Taenia solium)
  • Echinococcus spp.
  • Fasciola spp.
  • Filariasis (Wuchereria bancrofti, Brugia spp, Mansonella spp, Onchocerca volvulus, Dracunculus medinensis, Loa loa)
  • Gnathostoma spp.
  • Paragonimus spp.
  • Schistosoma (S. mansoni, S. haematobium, S. japonicum)
  • Strongyloides stercoralis
  • Toxocara spp.
• Life Cycle of Hookworms:

  • Adult worms copulate while attached to the mucosa of the small intestine
  • After copulation, adult female produces eggs, which are passed out in feces
  • Eggs embryonate on soil, Rhabditiform larva hatches from the egg
  • Rhabditiform larva starts feeding, molts, and transforms into filariform larva
  • Filariform larva penetrates the skin
  • Filariform larva migrates to the heart, lungs, alveoli, trachea, via the bloodstream
  • Filariform larva is swallowed back to the small intestine where it matures into an adult
• Diagnosis of Hookworm infection:

  • Standard method is by identifying hookworm eggs in a stool sample using a microscope
  • A concentration procedure is recommended for light infections
• Treatment of Hookworm infection:

  • Anthelminthic medications such as albendazole and mebendazole are the drugs of choice
  • Infections are generally treated for 1-3 days
  • Iron supplements may be prescribed if the infected person has anemia
• Prevention & Control of Hookworm infection:

  • Avoid walking barefoot in areas where hookworm is common
  • Avoid skin contact with contaminated soil
  • Avoid ingesting contaminated soil
  • Do not defecate outdoors
  • Effective sewage disposal systems
• Morphology of Hookworms:

  • Ova/Egg: All hookworm eggs are alike, ovoid with thin hyaline transparent shell, containing 2-8 germ cells
  • Adult worms are grayish white
  • Females are generally larger than males
  • Different species have specific characteristics in their buccal cavity and teeth arrangement
  • Adult male posterior end is expanded due to "Copulatory Bursa"
  • Female posterior end is pointed