Pathogenic Micro - Helminths

-eukaryotic
-multicellular animals
-chemoheterotrophic
-complex life cycles, passing through definitive and intermediated hosts
-Kingdom: Animalia
1. Phylum: Platyhelminthes (flatworms)
a. Class: Trematodes (flukes)
b. Class: Cestodes (tapeworms)
2. Phylum: Nematodes (roundworms)

-an organism that harbors the adult, sexually mature form of the parasite

-an organism that harbors the larval or asexual stage of the parasite

1. Mechanical obstruction or mass effect:
-intestinal obstruction
-lymphatic obsturction
-displacement of normal tissue
2. Faciliating bacterial invasion into normally sterile spaces
3. Anemia:
-from consumption of blood
-from vitamin B12 depletion
4. chronic inflammation

-normal bacterial flora restrict growth, but not very well
-no cell walls and fewer ubiquitously expressed PAMPs as seen with bacteria, viruses, and fungi
-innate immunity: Complement, PRRS, Phagocytosis (works only for eggs), cytokine and chemokine production, eosinophils, mast cells, neutrophils (lining up on worm body)
-adaptive immunity: B cells, T helper cells, antibody-dependent cell-mediated cytotoxicity

-Amebiasis, malaria, leishmaniasis, and toxoplasmosis: most induce Th1 responses; Leishmania can live in the phagosomes of macrophages and a Th1 response is required for its control
-Helminth worms: typically induce a Th2 response able to control infection; inappropriate Th1 responses in the gut lead to damaging inflammatory response; Th2 polariztion is mediated by the dendritic cell response to helminths

-can be acquired through ingestion of eggs, or penetration of intact skin by larvae

-humans are definitive host for Ascaris lumbricoides
-eggs are excreted in the stool, in warm environments, the eggs mature to an infectious stage over several weeks
-human fecally contimanted soil and food can be ingested, the eggs hatch in the small intestine to release larvae, the larvae invade the mucosa, enter the blood and lymph vessels
-larvae migrate to the lung, move up the trachea to be swallowed to gain entry back into GI tract, here the worms mature and reproduce (eggs)
-large worms burdens can produce a transient pneumonia from their presence in the lungs, and sometimes obstruction of the bile duct or peritonitis

-elevated blood levels of eosinophils, IgE, and the cytokine IL-5 can be indicative of helminth infections as compred with protozoan or other agents
-sometimes incidentally noticed by passing a worm
-can be diagnosised by examining the stool for eggs
-several anti-helminthic drugs, short-term, kill worms then pass them

-most common intestinal worm infection in the US
-readily transmitted from person-to-person through a fecal-oral route
-after ingestion, the eggs hatch in the small intestine, mature to adults in the large intestine and produce eggs, the eggs may be shed into the environment or inadvertently ingested by patients to their close contacts when fingers used to scratch the perianal area are licked or used to prepare food

-seldom cause serious disease, but do cause discomfort; most typical symtoms is perianal itching
-diagnosed by looking microscopically for pinworm eggs
-several anti-helminthic drugs exist for treating infection
-due to ease with which it spreads, everyone in close contact with an infected patient is usually treated

-intestinal nematodes - 2 species of roundworms: Necator americanus and Ancylostoma duodenale
-infect humans by larvae (filariform larvae) penetrating intact skin, transmission is through a fecal-cutaneous route = contact with soil contaminated by human stool filled with filariform larvae
-human hookworms spend little time in the skin as they invade the blood vessels and lymphatics
-spread to the lungs where they become trapped, larvae burrow into alveoli, get coughed up, and are swallowed to enter GI tract
-in small intestine, they mature to adult worms, undergo sexual reproduction and shed up to 20,000 eggs per day

-lead to chronic infection and anemia (the worms can live for several years)
-anemia from the worms sucking host's blood through the intestinal mucosa, severity of anemia is proportional to the worm burden
-diagnosed by microscopic exam of stool for the many eggs shed
-several anti-helminthic drugs exist for treating infection, dietary supplements of iron and folic acid can correct the anemia

-intestinal nematode S. stercoralis is prevalant in tropical areas
-worms can be trasmitted directly from human feces without any maturation in the environemtn
-like Hookworms, they penetrate intact human skin and migrate to the GI tract via a blood/lymph cessel to lung and swallowing route
-unlike Hookworms, Strongyloids lay eggs in the bowel wall, larvae hatch in the bowel lumen leading to autoinfection and also release of infective larvae in stool
-infections become chronic and vary in severity and symtoms, can have bacterial periotonitis due to worm invasion of intestine, pain, vomiting, and diarrhea with large warm burdens

-linked with more severe disease in immunosuppressed patients like transplant patients, indicateds a role for T cells and cell-mediated immunity in the control of the pathogen
-difficult to diagnose, eggs are rarely in the stool, can identify the larvae in stool and/or exam of duodenal contents or duodenal biopsy for worms, larvae, and eggs, can also use eosinophilia as diagnostic aid
-several anti-helminthic drugs exist for treating infections