Untitled

Medical Helminthology

• The scientific investigation of parasitic worms and their consequences on health.
• Laboratory diagnosis relies mainly on detecting and identifying eggs and larvae, with the detection of adults being rare.

Helminth Classification

• Nematodes (roundworms) are cylindrical worms that have separate sexes (bisexual).
• Trematodes are also known as flukes.
• Cestodes are also known as tapeworms.

Nematodes (Roundworms)

• Nematodes infecting humans can be intestinal, blood, or tissue nematodes.

Intestinal Nematodes

• Common intestinal nematodes include:
  • Ascaris lumbricoides
  • Trichuris trichiura
  • Enterobius vermicularis
  • Strongyloides stercoralis
  • Hookworms such as Ancylostoma duodenale and Necator americanus.

Ascaris lumbricoides

• It is also known as the large intestinal roundworm.
• The adult lives in the small intestine and they are worldwide in distribution.
• The eggs are very resistant to environmental conditions with adults living in the small intestine.
• Transmission occurs through ingesting food or water contaminated with embryonated eggs.
• Life Cycle:
  • Embryonated eggs are swallowed, larvae hatch, and penetrate the duodenal mucosa.
  • Larvae travel through the hepatic portal circulation to the liver, heart, pulmonary vessels, and lungs.
  • They break out of the alveoli into the air spaces, ascend the bronchial tree to the throat, are swallowed again, and reach the small intestine, where they mature.
  • Two to three months after infection, adult worms start laying eggs with up to 200,000 eggs per day.
• Clinical features & pathology:
  • Developing and mature worms in the intestine frequently cause abdominal pain.
  • Heavy infections, especially in children, may cause obstruction or perforation of the intestine.
  • Aberrant migration of irritated adult worms can cause damage to the bile duct, liver, pharynx, peritoneal cavity, and damage tissue.
  • Wanderings can occur in response to fever and drugs other than those used to treat ascariasis, and some anesthetics.
• Clinical Features:
  • During the lung phase, pneumonitis (Loeffler's pneumonia) occurs 5-6 days after exposure due to the penetration of lung capillaries by parasites.
  • The intestinal phase is 2-3 months after infection and causes:
    • Abdominal pain and diarrhea.
    • Nutrient malabsorption.
    • Stunted growth.
    • Cognitive impairment.
    • Intestinal obstruction by high worm numbers.
  • Wandering worms may cause pathogenesis effects like intestinal perforation, blockage of bile ducts, obstruction of the respiratory tract, and liver abscesses.
• Laboratory diagnosis involves the detection and identification of eggs in the stool via microscopy.
• Mebendazole is the drug of choice for treatment.
• Prevention and control includes:
  • Washing hands before eating and after defecation.
  • Avoid consumption of uncooked food contaminated by soil.
  • Sanitary disposal of faeces in latrines.
  • Avoiding the use of night soil as a fertilizer.
  • Mass de-worming programs are repeated at 3-6 month intervals in areas of high prevalence.

Trichuris trichiura

• Commonly known as whipworm.
• Adults live in large intestine (caecum) & appendix and are world-wide in distribution.
• Adults have a whip-like shape whereas the eggs as barrel shaped.
• Transmission: ingestion of embryonated eggs in contaminated food, water, or from contaminated hands.
• Life Cycle:
  • When embryonated eggs are swallowed, larvae are released in the upper duodenum.
  • They then attach themselves to the villi of the small intestine or invade the intestinal walls.
  • After 3-10 days, they move down to the caecum and ascending colon where they mature into adult worms.
• Clinical features and pathology are mainly determined by the worm burden.
  • Heavy worm burden:
    • Mechanical damage to the intestinal mucosa.
    • Chronic profuse mucoid and bloody diarrhea.
    • Abdominal cramps and severe rectal tenesmus.
    • Edematous prolapsed rectum, (in serious infection).
• Diagnosis: find characteristic eggs in faeces.
• Treatment of choice: Mebendazole.
• Alternative treatment: Albendazole.
• Prevention and control:
  • Sanitary disposal of faeces in latrines.
  • Avoidance of the use of night soil as a fertilizer.
  • Treatment of infected individuals and health education.

Enetrobius vermicularis

• Commonly known as pinworm.
• Cosmopolitan in distribution although more common in temperate climates and in children.
• Adults live in the caecum, appendix and adjacent portion of the ascending colon
• Habitat:
  • Eggs: deposited on the perianal skin and occasionally in faeces.
  • Gravid female: caecum and rectum.
• Transmission:
  • Person to person transmission (ingestion of eggs).
  • Exposure to viable eggs in the soil (ingestion- eggs remain viable for several weeks).
• Autoinfection: infecting the mouth with contaminated hands via scratching of the perianal area.
• Retro infection: the migration of newly hatched larvae from the anal skin back into the rectum.
• Life Cycle:
  • The ingested embryonated eggs hatch in the small intestine with the larvae migrates to caecal region where they mature into adults.
  • Gravid females migrate nocturnally outside the anus and oviposit on the perianal area.
  • Eggs have infective larvae between 4-6 hours of being laid, and induce perianal itching which causes scratching.
• Clinical features and pathology:
  • Nocturnal anal pruritus that is related to the migration of female worms from the anus onto the perianal skin.
  • Insomnia.
  • Nervousness.
  • Nightmares (particularly in children).
  • Abdominal pain or appendicitis resulting from the worms are considered rare.
• Laboratory diagnosis.
  • Detecting eggs from perianal skin using adhesive tape or swab method.
  • Detecting eggs in the faeces.
  • Finding of female worms from perianal skin or faeces.
• Treatment.
  • Pyrantel Pamoate
  • Mebendazole
  • The whole family should be treated to avoid reinfection.
• Prevention:
  • Treating all members of a family in which infection has occurred
  • Wearing tight-fitting cotton pants as well as washing anal skin and clothing.
  • Washing hands after toilet use and before eating.

Strongyloides stercoralis

• Commonly known as dwarf thread worm.
• Is world-wide in distribution.
• Has both free living and parasitic generations.
• Adults live in the mucosal epithelium of the small intestine.
• They are free living in both male and female forms in the external environments.
• Rhabditiform larvae is the diagnostic stage.
• Filariform larvae is the infective stage in the soil and water.
• Eggs: They are laid in submucosa, after which the rhabditiform larvae hatch.
• Transmission:
  • Commonly through skin penetration of the filariform larvae from the soil.
  • Internal or external autoinfection.
  • Transmammary.
• Life cycle:
  • Free-living (Indirect cycle): Rhabditiform larvae molts and develops as a free-living adult that produces rhabditiform larvae which are then transformed into filariform larvae.
  • Parasitic cycle (direct cycle): Rhabditiform larva molt into filariform larvae which penetrate heart then lung, causing the human host to excrete rhabditiform larva. These cause autoinfection.
  • Trans...
  • Parasitic cycle (direct cycle): is when rhabditiform larvae in stool molt into filariform larvae which penetrate skin. This then impacts the heart, lung, and then pharynx. They then get swallowed and develop into adult female with rhabditiform larva excreted in stool..
• Clinical features and pathology:
• Cutaneous phase: Large numbers of larva produce itching and erythema within 24 hours of the invasion.
• Pulmonary phase: larval migration stimulates lung symptoms including eosinophilia, broncho pneumonia, and full blown pneumonia. Some patients may be asymptomatic.
• Intestinal phase: Invasion may cause abdominal pain, mucoid diarrhea, nausea, vomiting, anemia and atrophy.
• Autoinfection is probably the mechanism responsible for long-term infection.
• Hyperinfection syndrome: massive larval is characterized by massive larval invasion of the liver or lung, including CNS, and can be fatal.
• Occurs when the host's immune is suppressed by drugs or malnutrition, or the has concurrent diseases.
• Laboratory diagnosis:
  • Detecting eggs from perianal skin that stick with adhesive tape or swab method.
  • Finding eggs in the faeces.
  • Finding the female worms from the area around the anus or faeces..
• Treatment is achieved through:
  • Pyrantel Pamoate
  • Mebendazole
  • It is important to treat the family

Hook Worms

• Are hematophagous nematodes.
• Two major species: Ancylostoma duodenale and Necator americanus.
• Geography: Found in sub and tropical countries with N. americanus as the most widespread hookworm globally.
• Habitat:
  • Adults: Jejunum (less often in the duodenum).
  • Eggs: faeces (not infective to human).
  • Eggs: are not infective to humans.
  • Rhabditiform; filariform larvae: are free in the soil and water with the latter the infective stage.
• Transmission and life cycle:
  • Infective filariform larva penetrates the skin, are carried through veins to the heart, then lungs. As they contact, the human host.
  • After penetrating into the alveoli ascending and getting swallowed, they reside in the small intestine. -They attach with resultant loss of blood.
• Clinical Features and pathology:
  • The dermal(cutaneous) triggers ground inch, or local erythema of macules.
  • Pulmonary infection includes migration of larvae and bronchitis.
  • Lastly, intestinal causes result mainly via adults worms, triggers resulting in possible upper -Intestinal injury or mucosa.
• In the Intestine, worms attach to the mucosa and feed on blood. Worms continuously exacerbate.
• Estimated daily blood loss, 0.03 ml ({N. americanus) 0.26ml (*{A.duodnale) per worm.
• Clinical:
  • Large exposure leads to anemia, but also malnutrition, development stall. -The result mainly includes
    • Iron deficiency anemia (microcytic,
• hypochromic), edema of the face and feet with decreased hemoglobin
• Head structure of different specia. The head is slightly bend (book) and the mouth has a characteristic teeth or cutting plates.
• Laboratory diagnostic:
  • Finding eggs in faeces is the most common method of -Microscopic identification of eggs.

Diagnosis

• Mebendazole or albendazole depending amount of blood loss.
• Prevention:
  • Similar to Strongyloides stercoralis the cycle.

Blood and Tissue Nematodes

• Includes:
  • Filarial nematodes
  • Dracunculus medinensis (Guinea Worm)
  • Trichinella species

Filarial Nematodes

• Common/pathogenic filariae include:
  • Wuchereria bancrofti
  • Brugia malayi
  • Brugia timori
  • Loa loa
  • Onchocerca volvulus
• Adults are long and require two hosts for the life cycle.
• Females give live birth to hatched larvae, and need infecting sucking inserts as an intermediate host to become infective.
• Includes the following categories disease types:
  • Lymphatic filariasis
  • Loiasis
  • Onchocerciasis
• Wuchereria bancrofti: causes most of word wide cases of Lymphatic Filariasis.
  • Social consequences includes debilitating conditions and stigmatized disfigurements.
  • Common result are disfigurements of the -limbs or genitals -mobility restrictions -travel limitation -decrease educational
• Clinical indications:
  • Bancroftian filariasis or Wuchereriasis, which results in Elephantiasis.
  • Can also be common found in countries countries including Ethiopia, being more common in areas near by the baro river.
• Adults are creamy and often and cause lymphatic inflammation and can result in : -Lower limb concerns. -diagnose in Peripheral blood near lungs and other internal organs. In gut

Trichinella species

• Infective larvae: in the gut and muscles including mouth parts of certain species of mosquito.
• Life Cycle includes a two host type. As L3 inject and grow, they have been shown to have microfilariae, which has found peripheral circulation at night.
• Mosquito ingests the microfilariae during blood meal from infected mosquito. The intermediate then goes thro muscles and forms L3
• Laboratory and diagnostic analysis include taking blood slides

Life Cycle

• Blackfly ingests the microfilariae during a blood meal.
• Microfilariae migrate from the black fly's midgut through the hemocoel to the thoracic muscles.
• 3Mf microfilariae develop in to L-migrate to the fly's proboscis. Infection occurs when the fly takes a blood meal

Clinical Features

Many microfilariae can result in inflammatory and toxic product damage Lymphangitis and high fever

• Clinical results:
• genital warts
• high levels of lipid deposits.
  • Laboratory, can check all serum/ plasma samples

Onchocerca volvulus

• Subcutaneous nodules and in the skin, the body releases fluids. The fluid is released of the
• Black fly and Simulium.
• During a feed, the female injects

Dracunculus medinensis

It exhibits an infection by means of larva injection

• Synonymous: Dracontiasis, Dracunvuliasis causative: Dracunculus, most commonly effects countries including India, Africa. It infects the gut and triggers
• It causes an injection
• Life cycle includes the stomach, which impacts the
• Female