Comprehensive Study Notes on Medically Important Nematodes

General Characteristics of Nematodes (Roundworms)

• Taxonomic Overview: Nematodes constitute the roundworms, representing the first group in the helminth series (which comprises nematodes, cestodes, and trematodes). They differ substantially in structural complexity from protozoan parasites.
• Species Diversity: There are more than $60$ species of nematodes.
• General Morphology:
  • They are non-segmented, elongated, and cylindrical worms, which gives them the common designation of roundworms.
  • Possess a highly developed digestive tract and reproductive system.
  • Adult nematodes exhibit separate sexes (dioecious).
• Sexual Dimorphism: As a universal rule of thumb, adult male nematodes are consistently smaller than adult female nematodes.
• Diagnostic Stages & Localization: Diagnostic eggs are typically recovered and identified within stool samples.
• Infective Stages and Entry Routes: Infective pathways vary by species, including:
  • Ingestion of embryonated eggs.
  • Direct percutaneous penetration by larvae that burrow through the skin and migrate internally to reach the intestine.
• Morphological Forms: Nematodes cycle through three distinct life stages:
  • Eggs (ova).
  • Larvae.
  • Adult worms (which acquire essential nutrients directly from the host).
• Clinical Severity Determinants: Symptoms and overall pathology depend upon several factors:
  • Overall worm burden (parasite load).
  • Nutritional status of the host.
  • Age of the host.
  • Duration of the infection.
  • Infections may also remain entirely asymptomatic.
• Nomenclature Standards: Organisms possess both scientific names and common names. Scientific names are mandatory for diagnostic clinical reporting, whereas common names serve primarily as informal terminology or slang.

Intestinal Nematodes: Ascaris lumbricoides

• Nomenclature & Significance: Ascaris ludricoides (also designated as Poscaris, Liscaris, Ascaris lembrocoides, or A. Lembroccoides) is commonly known as the intestinal roundworm. It is both the most common and the largest roundworm infecting humans.
• Epidemiology:
  • Demonstrates a worldwide distribution, with peak prevalence in tropical and subtropical regions characterized by warm climates and poor sanitation.
  • More than $1\text{ billion}$ people are infected worldwide.
  • Eggs strictly require a warm, humid environment in the soil to mature and become infective.
• Transmission & Environmental Maturation:
  • Classified as a soil-transmitted helminth (STH).
  • Transmission occurs primarily via the fecal-oral route, frequently through the ingestion of soil or agricultural produce where human feces is utilized as fertilizer.
  • Exhibits an indirect life cycle: transmission does not occur directly from one person to another. Freshly shed eggs are non-infective and must undergo an obligate environmental incubation period in the soil to embryonate.
• Internal Migration & Life Cycle:
  • Ingested embryonated eggs hatch within the duodenum of the small intestine.
  • Released larvae penetrate the host intestinal wall and enter the hepatic portal circulation.
  • Larvae migrate through the liver into the pulmonary circulation and lungs, penetrate into alveolar spaces, ascend the bronchial tree to the trachea, are swallowed, and return to the small intestine to mature into adult worms.
• Clinical Presentation:
  • Most infections remain asymptomatic.
  • Symptom severity correlates directly with infection duration, total worm burden, and overall host health.
  • In children, heavy worm burdens significantly impair physical growth and cognitive development due to inadequate hygiene and repetitive exposure.
  • Loeffler Syndrome: Characterized by marked pulmonary and peripheral eosinophilia induced by larval migration through lung tissue.
  • Ectopic Ascariasis: Occurs when adult worms wander and escape the intestinal lumen, entering the appendix, hepatobiliary tree, or pancreatic ducts, resulting in severe physical obstruction.
• Laboratory Diagnosis:
  • Demonstration of eggs in stool specimens via routine microscopic examination.
  • Adult females maintain an extremely high daily egg output, facilitating easy laboratory detection in feces.
  • Larvae may occasionally be recovered in sputum or gastric aspirates following larval pulmonary transit.
• Morphological Forms of Eggs:
  • Fertilized (Mammalated) Eggs: Contain infective developing larvae; characterized by a prominent, dark brown, bile-stained, bumpy (mammalated) outer albuminous coat.
  • Infertile (Decorticated) Eggs: Characterized by an elongated, regular oval shape, a thin shell, and the complete absence of the bumpy, dark brown, bile-stained outer layer.
• Adult Worm Morphology:
  • Adult Males: Much smaller than females, possessing a characteristic curved posterior end and three distinct anterior lips.
  • Adult Females: Considerably larger and longer than males, with a straight posterior end lacking any curvature.

Intestinal Nematodes: Enterobius vermicularis

• Nomenclature & Epidemiology: Enterobias vermicularis (also referred to as anaerobeas vermicularis) is commonly known as the pinworm.
  • Humans serve as the sole definitive host.
  • Extremely common in pediatric populations, with male children affected twice as often as female children.
  • Highly transmissible in conditions of institutional crowding, such as penitentiaries, boarding schools, dormitories, and within congested households.
  • In adult populations, infection is most frequently encountered in parents aged $30 - 39\text{ years}$, acquired directly from infected children aged $5 - 9\text{ years}$.
• Transmission Dynamics:
  • Infection occurs via ingestion or inhalation of infective ova.
  • Operates via a direct life cycle, enabling immediate transmission from host to host.
  • Eggs survive on fomites (such as contaminated bed linens, clothing, and environmental dust) for up to $3\text{ weeks}$.
  • Small, lightweight eggs easily become aerosolized, resulting in accidental inhalation followed by swallowing.
  • Under optimal environmental conditions, eggs become infective within $4 - 6\text{ hours}$ after oviposition.
  • Reinfection: Driven by the anus-to-mouth route when children scratch pruritic perianal skin and transfer eggs via contaminated fingers.
  • Retroinfection: Process in which laid eggs hatch directly on the perianal skin, and the emerging larvae migrate backward through the anus into the colon to mature.
• Clinical Features:
  • Intense perianal itching (pruritus ani), typically worsening at night.
  • Abdominal pain, nausea, and vomiting.
  • Nocturnal perianal migration occurs because the gravid female adult actively migrates out through the anal sphincter onto the perianal skin folds at night to deposit her eggs.
• Laboratory Diagnosis:
  • Cellulose Tape Preparation (Scotch Tape Prep): The primary diagnostic procedure. Clear cellulose tape is applied directly to the unwashed perianal region early in the morning before bathing or defecating; collecting at the wrong time frequently causes false-negative results.
  • Eggs are rarely discovered in routine fecal examinations.
  • Eggs may occasionally be identified in routine urine sediment as an incidental finding resulting from perianal contamination due to inadequate hygiene.
• Microscopic & Gross Morphology:
  • Egg Morphology: Measures approximately $50 - 60\text{ }\times\text{ }20 - 30\text{ }\times\text{ }10^{-6}\text{ m}$ ($50 - 60\text{ }\times\text{ }20 - 30\text{ }\times\text{ }10^{-3}\text{ mm}$ or $50 - 60\text{ }\times\text{ }20 - 30\text{ }\times\text{ }10^{-1}\text{ cm}$). Colorless, elongate-oval, and characteristically flattened on one side, resembling a flattened football.
  • Adult Females: Measure $8 - 13\text{ mm}$ in length, terminating in a sharply pointed, pin-like posterior tail (giving the parasite its name).
  • Adult Males: Markedly smaller than the female, exhibiting a strongly curved posterior end.

Intestinal Nematodes: Strongyloides stercoralis

• Nomenclature & Distribution: Strongyloides stercoralis is commonly known as the threadworm.
  • Endemic in tropical and subtropical regions across Asia, Latin America, and Africa.
  • Less prevalent than Ascaris or pinworm, but capable of producing lifelong systemic infection.
  • Adult worms inhabit the mucosal crypts of the small intestine.
• Biological Uniqueness:
  • Capable of existing indefinitely either as a parasitic worm in the human host or as an independent, free-living organism in the soil.
  • Adult parasitic females reproduce inside the human intestinal mucosa exclusively via parthenogenesis (asexual reproduction in which embryos develop from unfertilized eggs without male fertilization).
• Life Cycle Variations:
  • Direct Life Cycle: Infective filariform (felariform) larvae in the soil directly penetrate intact human skin (e.g., walking barefoot on contaminated soil or sand, or sand entering footwear such as flip-flops).
  • Indirect Life Cycle: Rhabditiform (rhabdidaform) larvae passed into soil mature into free-living adult males and females, producing subsequent generations in the environment.
  • Autoinfection: Non-infective rhabditiform larvae prematurely transform into infective filariform larvae while still inside the human body.
    • Internal autoinfection: Filariform larvae invade directly through the intestinal mucosa into the mesenteric circulation.
    • External autoinfection: Larvae penetrate the perianal skin after being voided in feces.
    • Autoinfection establishes chronic, persistent, lifelong infections lasting decades if unrecognized and untreated, and can escalate into fatal hyperinfection syndrome with systemic dissemination to ectopic organs.
• Migratory Route: Cutaneous penetration by filariform larvae leads to entry into venous capillaries, transport to the right heart, entry into the pulmonary capillaries, penetration into the alveolar spaces, ascension through the bronchial tree and trachea, and swallowing into the gastrointestinal tract, where worms mature in the small intestine.
• Clinical Pathology:
  • Cutaneous Manifestations: Known as larva curans; rapid, serpiginous, erythematous urticarial tracks developing beneath the skin surface caused by rapidly migrating filariform larvae.
  • Pulmonary Manifestations: Loeffler syndrome (Loffler syndrome) accompanied by high peripheral blood eosinophilia, cough, tracheal irritation, or overt pneumonia.
  • Gastrointestinal Manifestations: Diarrhea, constipation, abdominal pain, anorexia, vomiting, and severe mucosal ulceration/sloughing in heavy infections.
• Laboratory Diagnosis:
  • Eggs are almost never observed in stool because they hatch rapidly within the intestinal mucosa, releasing rhabditiform larvae prior to fecal evacuation (despite female egg production reaching up to $40\text{ eggs/day}$).
  • Diagnostic Stage: Rhabditiform larvae recovered in feces serve as the primary diagnostic finding.
  • Rhabditiform Larva Morphology: Very small (comparable in scale to a mustard seed or large sand grain), characterized by a distinctly short buccal capsule (mouth cavity), a prominent esophageal bulb, and a prominent genital primordium.
  • Filariform Larva Morphology: Larger than rhabditiform larvae, non-feeding, and characterized by a notched tail.
  • Fecal Agar Plate Culture: Diagnostic method where fresh stool is placed on a nutrient agar plate and incubated at room temperature for $48\text{ hours}$. Emerging larvae crawl across the agar, trailing bacteria and etching macroscopic tracks through the bacterial lawn. Highly sensitive for low worm burdens and distinguishes Strongyloides from hookworm.
  • Diagnostic Caution: A single negative stool examination never definitively excludes Strongyloides due to intermittent shedding and extremely low baseline larval numbers; serial stool examinations are required.

Intestinal Nematodes: Trichuris trichiura

• Nomenclature & Morphology: Trichuris trichuria is commonly designated as the whipworm due to its characteristic gross anatomy, which features an attenuated, thread-like anterior three-fifths and a stout posterior end resembling a coiled bullwhip.
• Epidemiology & Transmission:
  • Prevalent in warm, moist, tropical regions, particularly across South America, Africa, and Asia.
  • Frequently recovered in pediatric patients as a co-infection alongside Ascaris lumbricoides and hookworms.
  • Acquired via the oral ingestion of soil-embryonated eggs (soil-transmitted helminth).
  • Exhibits completely localized intestinal development without systemic or pulmonary tissue migration.
• Pathogenesis & Clinical Features:
  • Larvae hatch in the intestine and mature into adults that embed their thin, attenuated anterior ends directly into the colonic and cecal mucosa, feeding on tissue secretions and blood.
  • Infection elicits a local mucosal inflammatory response and marked peripheral eosinophilia.
  • Light infections remain completely asymptomatic.
  • Heavy chronic infections in pediatric patients manifest with chronic diarrhea, nausea, vomiting, abdominal pain, severe iron deficiency anemia, and mechanical rectal prolapse.
• Laboratory Identification:
  • Recovery and identification of characteristic eggs in fecal examinations. Adults are rarely seen in stool.
  • Adult females produce up to $20000\text{ eggs/day}$.
  • Exhibits a lengthy maturation period; egg shedding may not be detectable for up to $3\text{ months}$ post-infection.
  • Egg Morphology: Distinct barrel-shaped or football-shaped morphology with a thick, smooth shell and prominent, transparent, bipolar plugs (polar plugs at both ends).

Intestinal Nematodes: Hookworms (Necator americanus and Ancylostoma duodenale)

• Species Classification & Public Health Impact:
  • Nicator americanus (also spelled Decatur Americanus) represents the "New World hookworm."
  • Angostoma duodenale (also spelled Ankylstoma duodenale) represents the "Old World hookworm."
  • Hookworm infection ranks as the second most commonly reported helminthic infection in the United States and represents one of the most widespread human parasitic infections globally.
• Transmission & Internal Migration:
  • Infection occurs when infective filariform larvae residing in feces-contaminated soil actively penetrate unprotected skin (common in individuals walking barefoot).
  • Penetrating larvae enter the systemic venous circulation, travel to the lungs, cross into alveolar spaces, ascend the bronchial tree, are swallowed, and settle in the small intestine.
  • Larvae mature into adults, attach to the intestinal mucosal lining, and actively ingest host blood.
• Clinical Signs & Symptoms:
  • Ground Itch: Pruritic, erythematous maculopapular cutaneous lesions at the primary larval skin penetration site.
  • Respiratory Symptoms: Bronchitis, cough, and wheezing during intensive larval pulmonary transit.
  • Intestinal & Systemic Symptoms: Diarrhea, epigastric pain, nausea, fever, and severe chronic microcytic hypochromic anemia resulting from sustained blood loss.
• Laboratory Diagnosis:
  • Identified by detecting eggs or rhabditiform larvae in stool specimens.
  • Egg Morphology: Eggs of both hookworm species are indistinguishable. Eggs are large, oval, and surrounded by a thin, smooth, transparent shell. They characteristically contain an embryo at the $4 - 8\text{ cell stage}$ (cleavage morula), separated from the outer shell by a distinct, transparent clear space.
  • Diagnostic Differentiation Warning: Hookworm eggs share morphological similarities with Diphyllobothrium latum (Diphyllabothrium latum) ova and must be carefully differentiated microscopically.
  • Clinical Reporting: Because species-level distinction cannot be made from eggs alone, clinical laboratory results are reported non-specifically as "hookworm eggs."
• Species Differentiation Criteria: Precise differentiation requires adult worm recovery or specialized larval culturing:
  • Buccal Capsule Morphology: Necator americanus possesses ventral and dorsal semi-lunar, flat tetrad cutting plates; Ancylostoma duodenale possesses a buccal capsule armed with four sharp, pointed ventral teeth.
  • Adult Male Copulatory Bursa / Posterior Morphology: Necator americanus displays an elongated copulatory bursa structure with extended tail strands; Ancylostoma duodenale displays a blunt, short, pin-like tail arrangement.

Tissue Nematodes: Trichinella spiralis

• Geographic Distribution & Transmission:
  • Exhibits a cosmopolitan, worldwide distribution.
  • Acquired by ingesting raw or inadequately cooked meats containing viable, encysted (insisted) larvae.
  • Primary dietary source is domestic pork, but wild game meats—including bear meat, walrus, and horse meat—serve as significant transmission vehicles.
• Pathogenesis & Tissue Encystment:
  • Encysted larvae survive exposure to gastric acidity due to high resistance to gastric pH.
  • Upon entering the small intestine, larvae excyst, penetrate the intestinal mucosa, and develop rapidly into adults.
  • Adults mate and release newborn larvae that invade the local mucosa, enter mesenteric venules and the lymphatic circulation, and disseminate throughout the body.
  • Larvae selectively invade striated skeletal muscle fibers.
  • Within striated muscle, the invading larva reorganizes the skeletal muscle architecture, inducing the formation of a "nurse cell" complex.
  • The nurse cell sustains and nourishes the parasite while providing shelter against the host immune system.
  • Encysted larvae remain viable within nurse cells for several years before eventually undergoing calcification and death.
• Clinical Presentation (Trichinosis):
  • Intestinal Stage: Nausea, abdominal pain, constipation, or persistent diarrhea that can endure for up to $14\text{ weeks}$.
  • Systemic & Muscle Invasion Stage: Widespread myalgia, muscle tenderness, high fevers, periorbital edema, an intense systemic inflammatory reaction, and marked peripheral eosinophilia.
• Diagnostic Methods:
  • Detailed travel history, epidemiological exposure data, and clinical history of undercooked meat consumption.
  • Definitive identification via surgical muscle biopsy demonstrating encysted larvae (often difficult to collect depending on larval anatomical seeding).
  • Serological assays utilizing specific antibody detection serve as the primary diagnostic mainstay.

Tissue Nematodes: Toxocara canis and Toxocara cati

• Definitive Hosts & Transmission:
  • Toxocara canis infects canines (dogs); Toxocara cati infects felines (cats).
  • Infected definitive animal hosts pass non-embryonated eggs in their feces.
  • Transmission to humans occurs via accidental ingestion of embryonated eggs present in soil or sandboxes contaminated with animal excrement.
  • Pet owners and young children playing in dirt face the greatest risk of exposure.
• Pathogenesis (Aberrant Human Infection):
  • Ingested eggs hatch in the human small intestine, releasing larvae that penetrate the mucosal barrier and enter the circulation.
  • Because humans are non-permissive accidental hosts, Toxocara larvae cannot reach sexual maturity or complete their lifecycle in humans.
  • Larvae migrate continuously through various human visceral tissues and organs, provoking chronic inflammation and eosinophilic granulomas.
• Clinical Syndromes:
  • Visceral Larva Migrans (VLM):
    • Occurs primarily in preschool-aged children who exhibit geophagia or pica.
    • Larvae invade major visceral organs including the liver, lungs, skeletal muscle, and myocardium.
    • Clinical manifestations: persistent fever, myalgia, weight loss, cough, wheezing, urticarial skin rashes, hepatosplenomegaly, and high peripheral eosinophilia.
  • Ocular Larva Migrans (OLM):
    • Larvae migrate into the globe of the eye, lodging in the retina and uveal tract.
    • Causes eye lesions, retinal granulomas, localized inflammatory damage, and diffuse unilateral subacute neuroretinitis (DUSN), frequently culminating in permanent unilateral blindness.
• Laboratory Diagnosis:
  • Histological identification of wandering larvae via tissue biopsy (rarely achievable).
  • Serological detection of specific anti-Toxocara antibodies.

Tissue Nematodes: Dracunculus medinensis

• Nomenclature & Vector Transmission:
  • Dracunculus mendinensis is commonly known as the guinea worm; it is the causative agent of dracunculiasis.
  • Transmitted exclusively via the oral ingestion of unfiltered, stagnant freshwater containing tiny copepods (freshwater cyclopoid crustaceans) infected with third-stage larvae.
• Internal Development & Emergence:
  • Ingested copepods are degraded by gastric acid in the stomach, releasing active larvae.
  • Larvae penetrate the gastric and thoracic musculature, maturing into adult worms over an incubation period of $2 - 3\text{ months}$.
  • Following fertilization, the male worm dies; the gravid female worm slowly elongates and migrates through subcutaneous tissues toward the dependent extremities (most often the lower legs and feet).
  • Upon reaching the epidermis, the gravid female produces an intensely painful, burning cutaneous blister.
  • When the infected host immerses the affected extremity in cool water to soothe the burning pain, the blister ruptures, prompting the female worm to emerge and release millions of motile larvae into the water source.
  • If the adult worm dies in deep subcutaneous tissue without emergence, it becomes calcified.
• Treatment, Removal, & Complications:
  • There is no effective antihelminthic curative medication.
  • The traditional extraction procedure involves grasping the emerging female worm with a small wooden stick and manually rotating it a few centimeters each day, slowly winding the worm out of the subcutaneous tissue over several weeks.
  • Systemic symptoms during emergence include fever, nausea, vomiting, and diarrhea.
  • Ruptured blisters are prone to severe secondary bacterial infections.

Blood Nematodes (Filarial Worms): General Diagnostic Features

• Biology & Vectors:
  • Also known as filarial worms; transmitted to humans via the bites of blood-feeding arthropod vectors.
  • The larval stage develops within the insect intermediate host.
  • Adult worms inhabit the lymphatic channels, deep muscle tissue, subcutaneous nodules, or connective tissue of the human host.
• Microfilarial Production & Periodicity:
  • Gravid adult females produce living, motile larval offspring termed microfilariae.
  • Microfilariae circulate in the peripheral bloodstream or migrate through dermal tissue.
  • Many blood microfilariae exhibit temporal periodicity, circulating in peak numbers in peripheral blood at specific hours of the day or night matching the feeding patterns of their vectors.
• Microscopic Differential Identification Criteria: Species identification of circulating microfilariae relies upon two structural characteristics:
  • Presence or Absence of an External Sheath: Determination of whether the microfilaria is sheathed (enclosed in a transparent sheath) or unsheathed.
  • Tail Nuclei Arrangement: Distribution of cell nuclei within the posterior extremity (whether terminal nuclei extend fully to the tip of the tail, or if the tail tip remains clear of nuclei).

Diagnostic Features of Common Blood and Tissue Filarial Worms

• Wuchereria bancrofti:
  • Definitive Host & Vector: Humans are the definitive host; transmitted via the bite of infected mosquitoes.
  • Clinical Features: Causes lymphatic filariasis. Early stage presents with flu-like symptoms, fever, chills, headache, and acute lymphangitis/lymphadenitis. Chronic late stage causes irreversible lymphatic obstruction, fibrosis, and severe elephantiasis.
  • Periodicity & Specimen Collection: Displays strict nocturnal periodicity; optimal diagnostic blood collection occurs at night between $10\text{ PM}\text{ and }2\text{ AM}$.
  • Microscopic Morphology: Microfilariae possess an external sheath; nuclei do not extend to the tip of the tail (terminal tail tip is empty).
• Brugia malayi (Brugia melii):
  • Vector & Geographic Range: Transmitted by mosquitoes; predominantly endemic in the Far East (Asia).
  • Clinical Manifestations: Induces lymphatic damage and elephantiasis similar to Wuchereria bancrofti, but localized swelling is typically confined below the knees.
  • Strains & Periodicity: Exists in two distinct epidemiological forms: a nocturnal periodic form (associated with coastal rice fields) and a non-periodic/subperiodic form (associated with swampy forests). Specimen collection for the nocturnal form must be performed at night between $10\text{ PM}\text{ and }2\text{ AM}$.
  • Microscopic Morphology: Microfilariae possess an external sheath; the tail demonstrates two distinctly separated, terminal nuclei at the posterior tip. This nuclear interruption differentiates Brugia from Loa loa.
• Loa loa:
  • Common Designation & Vector: Commonly known as the African eyeworm; transmitted by biting tabanid flies (deer fly, Chrysops). Infective larvae leave the fly mouthparts during feeding and enter through the bite wound.
  • Endemic Regions: Confined to the tropical rainforest zones of West and Central Africa.
  • Clinical Features: Characterized by Calabar swellings (transient, localized, painful subcutaneous inflammatory angioedema caused by wandering adult worms) and direct migration of the adult worm across the subconjunctiva of the eye.
  • Periodicity & Specimen Collection: Displays diurnal periodicity; diagnostic peripheral blood collection must take place midday between $10\text{ AM}\text{ and }12\text{ PM}$.
  • Microscopic Morphology: Microfilariae possess an external sheath; nuclei extend continuously in a solid column all the way to the tip of the tail.
• Onchocerca volvulus (OncoCerca):
  • Vector & Distribution: Transmitted by the black fly (Simulium); endemic throughout Africa, Central America, and South America.
  • Pathology & Manifestations: Adult worms inhabit firm fibrous subcutaneous nodules (onchocercomas). Microfilariae migrate through the skin and ocular structures, invading the cornea to produce sclerosing keratitis, chorioretinitis, and permanent blindness (known as river blindness), alongside severe pruriginous dermatitis, skin atrophy, and localized lymphadenopathy.
  • Diagnostic Approach: Diagnosed by microscopic examination of superficial skin snips or direct visualization of microfilariae in the anterior chamber of the eye; microfilariae do not circulate in routine peripheral blood.
  • Microscopic Morphology: Microfilariae lack a sheath (unsheathed) and possess non-nucleated, tapered tails.
• Mansonella Species (Mancinella / Manzanella / myalcinella):
  • Vector: Transmitted by biting midges (small biting flies, Culicoides).
  • General Characteristics: Distributed across tropical zones of Africa, South America, and Central America; generally cause low-virulence or asymptomatic infections. Symptomatic individuals experience cutaneous rashes, altered skin pigmentation, and localized edema of the face and arms. Microfilariae of all Mansonella species lack a sheath (unsheathed).
  • Mancinella streptocerica: Resides primarily in the dermal tissues of the skin; microfilariae cause cutaneous pruritus and rashes.
  • Mancinella purstens: Adults inhabit body cavities, residing predominantly in the pericardial, pleural, and peritoneal cavities; microfilariae circulate in peripheral blood.
  • Manzanella osardi (myalcinella osardii): Endemic to Central America, South America, and the Caribbean Islands; microfilariae circulate in the peripheral blood.