Helminths and Nematodes

Introduction to Helminths

• Helminths are multicellular
• The parasitic worms fall into 3 main groups: nematodes, trematodes, and cestodes.

Nematodes

• Nematodes have 2 separate sexes (male and female). Characteristics include:
• Cylindrical body shape
• Separate sexes
• Females tend to be larger than males
• They are bilaterally symmetrical and oviparous
• They possess digestive, excretory, nervous, and reproductive systems
• The life cycle comprises 4 larval stages and an adult stage
• Examples of intestinal nematodes include: Ascaris lumbricoides, Necator americanus, Ancylostoma duodenalis, Strongyloides stercoralis, Trichuris trichiura, Enterobius vermicularis, and Trichinella spiralis
• Examples of tissue nematodes include: Wuchereria bancrofti, Brugia malayi, Onchocerca volvulus, Mazonela ozzardi, Manzonela perstan, Loa loa, and Dracunculus medinensis

Ascaris lumbricoides

• Ascaris lumbricoides is a roundworm
• Humans act as the only host for Ascaris lumbricoides
• It is cosmopolitan, found in the tropics and temperate zones
• Small intesting habitat:
• Adult females measure 20-35 cm x 1 cm and males are smaller
• Infection occurs through the ingestion of eggs containing L2 larvae
• Symptomatology includes:
• Pre-patent phase: often asymptomatic, cough, fever, eosinophilia, and Loffler's syndrome
• Patent-phase: malnutrition, impaired physical growth, abdominal pain, intestinal and biliary tract obstruction, and pancreatitis
• Diagnosis is via the presence of fertilized and unfertilized eggs in feces
• Treatment involves Albendazol or Mebendazol
• Ascaris lumbricoides can create an intestinal blockage
• Worms can knot, causing a blockage which could be fatal

Hookworms

• Hookworms include Ancylostoma duodenale and Necator americanus
• Hookworms adhere to the endothelia and cause anemia
• They are cosmopolitan
• Can occur in the tropics and temperate zones
• Hookworms live in the mucosa of the upper small intestine
• Adult females measure 9-13mm; adult males measure 5-11mm
• Transmission occurs when a filariform (L3) larva penetrates the host's skin
• Symptoms include: ground itch, cough, abdominal pain, severe anemia, distended abdomen, loss of appetite, and stunted growth
• Diagnosis is via the presence of eggs in feces
• Treatment involves Albendazole and iron (Fe) supplementation

Strongyloides stercoralis

• Strongyloides stercoralis creates autoinfection, where the infection can worsen and persist even with treatment
• It is cosmopolitan and found in the tropics and temperate zones
• Habitat: mucosa of upper small intestine
• Adult parthenogenetic females are 2-2.5mm
• Transmission: Penetration of skin by filariform (L3) larvae
• Symptoms: ground itch, cough, vomiting, diarrhea, autoinfection in immunocompromised patients, and HTLV-1 association
• Diagnosis: presence of rhabditiform larvae in feces
• Treatment: Albendazole or Ivermectin
• Ground itch and cutaneous larva migrans can occur
• This life cycle includes eggs in feces (hookworms) and/or rhabditiform larvae (strongyloides)
• Maturation to the infective stage (L3 larvae, filariform) occurs in the environment
• The infective larva penetrates skin, migrates and develops in the lungs, and ascends by trachea to pharynx and esophagus to the small intestine
• Then, maturation to an adult worm occurs in the intestine

Trichuris trichiura

• Trichuris trichiura is also known as whipworm
• Cosmopolitan distribution in the tropics and temperate zones
• Site of infection: mucosa of the large intestine
• Size: Females measure 30-35mm; males are smaller
• Mode of infection: ingestion of eggs containing L2 larvae
• Infection produces bloody stools, abdominal pain, weight loss, rectal prolapse, moderate anemia, and nausea
• Diagnosis: presence of eggs in feces
• Treatment: Albendazole or Mebendazole

Enterobius vermicularis

• Enterobius vermicularis causes itching
• This is because, in children, infection causes restless behavior due to itching
• Short life on average, and infection is easy to resolve in humans
• Cosmopolitan distribution in the tropics and temperate zones
• Habitat: large intestine
• Size: Females measure 8-13mm; males measure 2-5mm
• Transmission: ingestion of eggs containing L1 larvae
• Symptoms: itching and irritation around perianal and vaginal areas, sleeplessness, teeth grinding, and abdominal pain
• Diagnosis: recovery of adults or eggs from the perianal region
• Treatment: Albendazole or Pyrantel Pamoate

Wuchereria bancrofti and Brugia malayi

• Wuchereria bancrofti and Brugia malayi cause lymphatic filariasis
• The adults of these species appear as threads and are found in lymphatic nodules
• The larvae do not get passed in feces, but instead reside in the plasma.
• A person with lymphatic filariasis will have a long prepatent period and might not realize they are infected for >1 year
• Causes lymphangitis
• These species of worms are transmitted via mosquitoes
• Wuchereria bancrofti causes Bancroft's Filariasis
• It dwells in the blood and lymphatics
• The infection results in elephantiasis
• Vectors: Culex, Aedes, and Anopheles mosquitoes
• The diagnosis for Wuchereria bancrofti involves detection and identification of microfilaria in stained blood smears and exhibits a marked circadian migration, best seen at night
• Microfilariae are sheathed, and the nuclear column does not extend to the tip of the tail
• Cosmopolitan distribution in tropics and temperate zones
• They live in the afferent lymphatic system
• F: 8-100 mm x 0.2-0.4 mm, M: 40mm x 0.1 mm
• The mode of infection is injection of filariform larvae (L3) by mosquito
• Symptoms: chills, fever, localized swellings, inflammation of testes and lymph areas of lower body
• Diagnosis includes the presence of microfilariae in peripheral blood
• Treatment: Diethylcarbamazine (DEC) or Ivermectin

Onchocerca volvulus

• Onchocerca volvulus causes blindness
• Tropical areas of Africa, Central and South America are common hosts
• Size of habitat is adults in subcutaneous nodules
• F: 35-50 cm x 0.3-0.4 mm
• M: 19-42 mm x 0.13-0.21 mm
• Mode of infection: injection of filariform larvae (L3) by simuliid fly
• Symptoms are nodule formation, dermatitis, visual impairment, and blindness
• Diagnosis: presence of microfilariae in skin snips
• Treatment: surgical removal of nodules or Ivermectin

Trematodes

• All trematodes are hermaphroditic
• Intestinal trematodes include: Fasciolopsis buski, Echinostoma spp, Heterophyes heterophyes, and Metagonimus yokogawai
• Tissue-inhabiting trematodes include: Schistosoma mansoni, S. haematobium, S. japonicum, Fasciola hepatica, Paragonimus westermani, and Clonorchis sinensis
• Trematodes general characteristics:
• Flattened dorsoventrally
• Bilaterally symmetrical
• Most have incomplete digestive tract
• Posses two suckers
• Lack a body cavity
• Lack a special skeletal, respiratory, or circulatory system
• Most are monoecious, some are diecious
• All reproduce sexually and most reproduce asexually during larval stages
• Have some regenerative ability
• Have an indirect life cycle, 1 or more intermediate hosts, and a mollusk is the first intermediate host

Schistosoma mansoni

• Caribbean countries, eastern Mediterranean countries, South American countries and most countries of Africa are common hosts
• Adults live in blood vessels (mesenteric veins) near the human intestine
• F: 7-17 mm, M: 6-12 mm
• The mode of infection is skin penetration of cercariae
• Symptoms: fever, abdominal pain (liver/spleen area), bloody diarrhea or blood in stools, cough, malaise, headache, rash, body aches
• Diagnosis: presence of eggs in feces
• Treatment: Praziquantel

Fasciola hepatica

• Is abundant in the world
• Exists in herbivores that eating certain weeds of weed-like plants
• Lives in the liver
• Cosmopolitan, meaning there is a worldwide distribution
• It’s habitat is in the bile ducts of the liver
• Adults: 30mm length and 13mm width
• Mode of infection: Ingestion of infective metacercariae cyst
• Symptoms: Intermittent fever, hepatomegaly, abdominal pain primarily in the upper-right section of the abdomen, malaise, and wasting.
• Diagnosis: presence of eggs in feces
• Treatment: Triclabendazole, Bithionol

Cestodes

• Are also hermaphrodites
• By Adults:
• Taenia solium
• Taenia saginata
• Diphylobotrium latum
• Hymenolepis nana
• Hymenolepis diminuta
• By Larva:
• Cysticercosis (Taenia solium)
• Hydatic Cyst (Echinococcus granulosus)
• Coenuro (Multiceps multiceps)
• Consists of:
• Scolex: suckers, hooklets and grooves at it's head, and is how they attach to the intestine
• Neck: germinal portion of the worm
• Strobila: Immature, mature and gravid proglottids (segments)
• General Characteristics:
• Intestine Dwellers
• Flat and segmented worms
• Segments consist of hermaphroditic (proglottids)
• Contain a scolex
• Can be suckers or bothrias
• Lacks a mouth and intestine
• Covered in an absorptive surface
• Have an indirect life cycle
• Can have an armed rostellum
• Diagnosis involves the observation of eggs or free proglottids in feces
• Taenia saginata can regenerate
• A General Life Cycle:
• Cow/pigs are an intermediate host and humans are the final host
• Animals are required to eat the worms/eggs
• If humans eat the eggs nothing will happen
• Symptoms:
• Can inhabit a small intestine
• T solium can affect tissue (brain,eyes etc)
• Known to cause taeniasis and cysticercosis

Infection and Remedies

• T.saginata Infective Stage is: -Larva

• Cysticerscus Bovis

• T.solium Infective Stage is: -Larva

• Cysticerscus Cellulosae

• Pathogenesis:

• Taeniasis (is infected by eating cysticerus) factor: adult worm

• Deprivation of nutrition

• Disfunction of the intestine: vomiting or diarrhea

• Allergic reactions

• Appendicitis

• Obstructions of the intestine

• Cysticercosis, is known to vary with symptoms and intensity of the infection

• Symptoms includes headache, dizziness, epilepsy and blurred vision

• Diagnosis

• By finding of eggs in feces or perianal area

• Finding proglottids in stool

• Differentiation of species will be performed by the segments

• Treatment for infection/worms involves:

• Praziquantel

• Niclosamida destroys the adult worm

• Essential treatment step is to eliminate the scolex (worm section)

• Prevention: Cook meat over 57°