STEPTRACKERMICROBIOLOGY + PHARMACOLOGY | NEMATODES | HIGH-YIELD REVIEW

Nematodes (Roundworms)

Sort roundworms by how they get in — swallowed eggs, swallowed larvae in meat, larvae through skin, or insect bites — and by whether they live in the gut or the tissues.

FOCUS ON
Ingested eggs: Enterobius (perianal itch at night, tape test), Ascaris (lung migration then bowel obstruction), Trichuris (rectal prolapse), Toxocara (visceral/ocular larva migrans). Ingested larvae: Trichinella (undercooked pork/bear → myositis, periorbital edema, eosinophilia). Skin penetration: Strongyloides (autoinfection; hyperinfection with steroids/HTLV-1), hookworms (Necator, Ancylostoma → iron deficiency anemia; cutaneous larva migrans). Insect bite: Onchocerca (black fly → river blindness), Loa loa (deer fly → eye worm), Wuchereria (mosquito → elephantiasis). Treatment: mostly albendazole/mebendazole (gut) or ivermectin (Strongyloides, Onchocerca); diethylcarbamazine for Loa and Wuchereria.
WORM
ROUTE · LIFE CYCLE
CLINICAL PICTURE
DIAGNOSIS · TREATMENT
Enterobius vermicularis (pinworm)
Eggs by fecal-oral, autoinfection; females lay eggs at anus at night
Nocturnal perianal itching in children, vulvovaginitis
Scotch-tape test · albendazole/mebendazole or pyrantel; treat household
Ascaris lumbricoides
Eggs ingested → larvae migrate through lungs → swallowed → adults in gut
Löffler pneumonitis (cough, eosinophilia) → bowel or biliary obstruction
Knobby eggs in stool · albendazole
Trichuris trichiura (whipworm)
Eggs ingested; adults in colon
Dysentery, rectal prolapse in children, anemia
Barrel-shaped eggs with plugs · albendazole
Toxocara canis / cati
Eggs from dog/cat feces (sandboxes); larvae wander, can't mature
Visceral larva migrans (hepatomegaly, eosinophilia, wheeze) · ocular (leukocoria, mimics retinoblastoma)
Serology · albendazole
Trichinella spiralis
Larvae encysted in undercooked pork or wild game (bear) → adults in gut → larvae to striated muscle
GI upset → fever, myalgia, periorbital edema, splinter hemorrhages, very high eosinophils, ↑ CK
Muscle biopsy, serology · albendazole + steroids
Strongyloides stercoralis
Larvae penetrate skin (barefoot) → lungs → gut; autoinfection keeps cycle going for decades
GI symptoms, eosinophilia, larva currens rash · hyperinfection with steroids or HTLV-1 → gram-negative sepsis/meningitis
Rhabditiform larvae in stool, serology · ivermectin · screen before steroids
Hookworms (Necator, Ancylostoma)
Larvae penetrate skin → lungs → small bowel; adults suck blood
Microcytic iron-deficiency anemia, pruritic "ground itch"
Eggs in stool · albendazole + iron
Cutaneous larva migrans
Dog/cat hookworm larvae (A braziliense) in beach sand; can't go deeper
Serpiginous, intensely itchy, slowly moving track on feet
Albendazole or ivermectin
Onchocerca volvulus
Female black fly near rivers (Africa)
Itchy skin nodules, hyper/hypopigmentation; microfilariae in eye → river blindness
Skin snips · ivermectin (doxycycline kills Wolbachia)
Loa loa
Deer fly (Chrysops), Central/West Africa
Calabar swellings; adult worm crossing the conjunctiva
Diethylcarbamazine · ivermectin can cause encephalopathy with high loads
Wuchereria bancrofti · Brugia
Mosquito; adults in lymphatics, nocturnal microfilariae
Lymphangitis → elephantiasis, hydrocele; tropical pulmonary eosinophilia
Night blood smear · diethylcarbamazine
Dracunculus medinensis
Copepods in drinking water
Painful blister as worm emerges from the leg
Slowly wind worm out · near eradication

Mechanism — why tissue worms cause eosinophilia

Large migrating larvaeToo big to phagocytose
→
Th2 responseIL-4, IL-5, IL-13
→
IgE coats worm, ↑ eosinophils
→
ADCC: major basic protein

Eosinophilia is marked with tissue migration (Trichinella, Strongyloides, Toxocara) and minimal with gut-only pinworm.

Route of entry

ROUTE
WORMS
DRUG
Swallowed eggs
Enterobius, Ascaris, Trichuris, Toxocara
Albendazole
Swallowed larvae in meat
Trichinella
Albendazole
Through skin
Strongyloides, hookworms
Ivermectin · albendazole
Insect bite
Onchocerca, Loa loa, Wuchereria
Ivermectin · DEC

How it's tested

COMMON CONFUSIONHookworm (iron-deficiency anemia, eggs in stool) vs Strongyloides (larvae in stool, autoinfection, hyperinfection risk) — both enter through the skin.
THE TRAPStarting high-dose steroids in a patient from an endemic area without screening for Strongyloides can trigger fatal hyperinfection.
YOUR APPROACHEosinophilia ± symptoms → exposure route → gut vs tissue → stool/blood/skin test → albendazole, ivermectin or DEC.

If you see… think…

Child with nighttime perianal itching → Enterobius (tape test)
Cough and eosinophilia, then bowel obstruction → Ascaris
Child with rectal prolapse and dysentery → Trichuris
Toddler with eosinophilia, hepatomegaly and leukocoria, puppy at home → Toxocara
Bear meat → fever, myalgia, periorbital edema, huge eosinophils → Trichinella
Sepsis with gut bacteria after steroids in an immigrant → Strongyloides hyperinfection
Iron-deficiency anemia in a barefoot farm worker → hookworm
Itchy creeping track on foot after a beach holiday → cutaneous larva migrans
Blindness and skin nodules near African rivers → Onchocerca (ivermectin)
Worm crossing the eye → Loa loa