Chapter 12: Parasites
TRANSMISSION -American trypanosomiasis may be transmitted through blood and organ transfer, congenitally, but most often by vector. -First the kissing bug watches you breathe...
CONTROL -Kissing bugs love unfinished or shoddy construction, reducing this is the primary control mechanism. -Blood screening. -Before blood screening many South American nations had contaminated blood at rates up to 20x higher than HIV and hepatitis
T. VAGINALIS -Once it attaches to cells lining the host's urinary or genital tract, it flattens out and begins to ingest the cells, as well as white and red blood cells.
GIARDIA LAMBLIA -Giardiasis can occur through ingestion of dormant cysts in contaminated water or food, or by the faecal-oral route . -The lumen of the small intestine is infected causing self-limiting but serious gastrointestinal symptoms. These include villous atrophy, pain, explosive diarrhea and blood or pus in the stool.
PARASITISM The parasite may do harm to the host by: Mechanically damaging, chewing, boring, digging. Stimulating or damaging inflammatory and immune responses. (Some evidence supports the new theory that some parasites assist the immune system) Stealing nutrients.
IF YOU'RE NOT A PARASITE... ...you're a host. Nearly every animal on Earth is infected, most of the parasites have their own parasites. Humans can be infected by more than 100 types of parasites including: Flagellates, amoebas, ciliates, worms, lice, fleas, ticks and mites.
WHY DIDN'T I KNOW THAT?!? -Most parasites are tropical diseases. -Frequently people in temperate climates know little about them or the magnitude of the problem. -In 1980, 209$ was spent per case of cancer on research. -8$ for cardiovascular disease. -4.5 cents for schistosomiais.
IN THE US -In 1990, 55,612 deaths were attributed to parasitic disease, compared to 79,518 for influenza AND pneumonia. -JAMA -Increasing prevalence addressed in an August,2009 WSJ article, citing a lack of education in US physicians. -Many US GPs claim to have treated every major parasitic illness in the life of a practice.
PHYLUM PLATY HELMINTHES-FLATWORMS -All flatworms are dorsoventrally flattened. -They absorb nutrients through their non-living outer covering, the cuticle. -The two major groups of flat worms are tape worms and flukes. There are many types of each.
LUNG FLUKES Paragonimus westermani -The lung flukes' intermediate host are Crayfish. -Humans are a definitive host, and for the life cycle to continue, eggs from the lungs in sputum must somehow reach water.
NAEGLERIA FOWLERI-AMOEBAZOA -Known colloquially as the brain eating amoeba, this one really isn't trying to hurt you. -Normally living in warm fresh water, these can cause infection if the enter through the nose. -From here they cause hemorrhage and necrosis of the olfactory bulb, climb nerve fibers to the brain and digest brain cells individually.
N. FOWLERI
BIG AND LITTLE? -Macroparasites(ticks, fleas, tapeworms, arthropods, and many nematodes and trematodes) do not multiply in or on the host! -Microparasites(all the others) *do* multiply within the host. These are also generally smaller.
OBLIGATIONS -Most parasites are obligate, requiring a host for at least one part of their life-cycle.?These frequently have at least one free living stage. -Some are facultative, living without a host unless introduced accidentally
PARASITES, THE LEAST FRIENDLY SYMBIONT. In this relationship, one organism benefits at the expense of the other. Many disease causing organisms fall into this category. Why?
PARASITES There are more parasitic than non-parasitic organisms in the world. Even if you don't count the viruses OR bacteria. Which we will NOT. Parasites in microbiological study are eukaryotic (generally animal) organisms. Nearly every phylum of animals has a parasitic member, and many plants.
PHYLUMNEMATODA -Nematodes, the round worms, are tapered at each end. -They have a complete digestive system including mouth, intestine and anus. -Most species are dioecious.
PINWORMS -Pinworms (Enterobius vermicularis) spend their whole lives in human hosts. -Thought to be the most common parasitic infection in the US. -Adults live in the intestine, but females lay their eggs on perianal skin. -These can be passed through contact or clothing/bedding. -The test for pinworms involves tape.
THE BIG TWO Important parasites are largely grouped into two categories. -Protozoans -'first animals'. -Helminths -worms.
PROTOZOANS -This group is likely to be reorganized. -They currently represent 30-40 quite different phyla. Very generally they: -Are unicellular -Have some kind of life cycle -Are heterotrophic -Motile at some stage Some are capable of forming cysts
AMERICAN TRYPANOSOMIASIS -Caused by Trypanosoma cruzi, of the phylum Euglenozoa. -Like the African version (African trypanosomiasis), the disease is spread by an arthropod vector. In this case, triatomids, or kissing bugs (aka assassin bugs) rather than tsetse flies.
SYMPTOMS -Acute -local swelling within days or weeks. Parasitemia. Fatigue, Romaña's sign, rare complications. -Chronic -30% symptomatic. Follows untreated acute illness. Most commonly death is a complication of heart muscle damage from intracellular parasite division. -CNS or digestive symptoms may also occur.
PHYLUM PLATYHELMINTHES- CLASS CESTODA -The Cestodes are tape worms. -These have a distinctive structure involving a head (scolex) equipped with suckers and possibly hooks for attachment. -Their body is composed proglottids,each containing male and female organs (monoecious). -Whole mature proglottids are shed from the end of the organism, and are infective to a new host.
TAENIA SAGINATA-BEEFTAPEWORM -Beef tapeworms can be as long as 36 feet in the intestine. -Proglottids are released in feces, and can wriggle (in pasture situations this helps them get to ingestible grass) -In cows, consumed eggs hatch, and larvae burrow into the intestinal wall, eventually forming cysts (cysticerci) in the meat. -When these cysts are eaten, all but the scolex is digested, this bit attaches and begins again.
THE HELMINTHS -These are divided into two primary phyla (with a few outliers): The flatworms, Platyhelminthes -The roundworms, Nematoda All are advanced multicellular Eukaryotes with digestive, circulatory, nervous, excretory and reproductive systems.
THAT SAID... -Pathogenic helminths often have changes in these systems. -Digestive systems are reduced or eliminated, nutrients are absorbed directly from the host. -Nervous system reduced, the environment in a host is constant, they have little to respond to. -Locomotion reduced or lacking, they don't need to actively search for a suitable habitat. -Reproductive systems complex, HUGE numbers of eggs help them get from host to host.
A NOTE ON HOSTS Hosts are differentiated based on the role they play in the parasite's life cycle. Definitive hosts harbor the parasite as it reaches sexual maturity Intermediate hosts are required for parasite development, but other stages Paratenicor transport hosts only harbor the parasite until it can be passed to a different host. The parasite does not develop. Any animal that harbors a parasite which can be transmitted to humans is a reservoir host, regardless of its other host status.
THE IMPACT ON HUMANS -These are a very few of the human parasitic infections. -Together, the current prevalence means that there are more than enough active pathogenic infections for every person to have at least one.
PHYLA DIPLOMONA / PARABASALIA -These interestingly lack mitochondria, but have mitosomes which are similar but lack DNA. -They generally have two or more front facing flagella. -Many are digestive symbionts in mammals.
TRICHOMONAS VAGINALIS The most common pathogenic parasite in developed countries with 180 million cases worldwide. -Sexually transmitted. -Causes green frothy vaginal secretions and itching, as well as pre-term delivery and low birth weight. -May also travel causing pneumonia, bronchitis and oral lesions.
MACROPARASITES -One group of these, the arthropods, are of little interest to us as parasites. -Arthropods have jointed legs, exoskeletons and segmented bodies. (spiders, mites and insects) -While a few can cause disease, they are more important in the transmission of disease, as *vectors*.
VECTORS -Animals, especially insects that carry pathogens. -Mechanical vectors simply transmit pathogens. -Biological vectors experience pathogen replication within their bodies, depositing large numbers on a new host through saliva or feces.
IN AND OUT Parasites on the outside of the body, the surface of the host, is an *ectoparasite*. Internal parasites are *endoparasites*
VERTEBRATE PARASITES -Parasites living in a hollow organ, like the intestinal lumen are said to be coelozoic. -Those in tissue are histozoic.
