Beware of potentially graphic content. Parasites Beware of potentially graphic content.

Helminths - WORMS Life Stages egg, larva, adult; complex life cycles infective stage: egg or larva definitive host: harbors adult stage intermediate hosts: may be more than one Classifications: Nematodes - roundworms Platyhelminthes - flatworms Trematodes - flukes- nonsegmented Cestodes - tapeworms- segmented

Cestodes, including tapeworms, have a head region called a scolex. Tapeworms generally live in the host’s intestine, absorbing nutrients and absorb directly. Figure 18 (C) T. saginata showing the suckers and hooks © Dennis Kunkel Microscopy, Inc./Phototake/Alamy Images

Tapeworms survive in the human intestines. Beef and pork tapeworm disease are caused by Taenia saginata and Taenia solium, respectively. They are acquired by eating poorly cooked beef or pork. The scolex attached to the intestine, causing obstruction and mild diarrhea. Longest is 37 feet long. .

Figure 19: Roundworms in intestines. Roundworms (Phylum Nematoda) live in every habitat on Earth. Damage to the host often occurs by large worm burdens in vessels or intestines. Figure 19: Roundworms in intestines. © R.F. Ashley/Visuals Unlimited

Nematodes - roundworms Ascaris lumbricoides- adult stage

Trichinella spiralis - roundworm

Enterobius vermicularis – Pinworms – a type of roundworm Figure 12.29

Hookworms have a set of hooks or suckers to attach to the upper intestine. Hookworms suck blood from intestinal capillaries. This causes blood loss and anemia. Humans are the only host. Larvae in soil penetrate the skin of bare feet and enter the bloodstream. You get this by playing outside without shoes on. Figure 24: A Hookworm. © Dennis Kunkel Microscopy, Inc./Phototake/Alamy Images

Figure 26: Elephantiasis. Filariasis is caused by Wuchereria bancrofti. It is transmitted by mosquitoes. Larvae infect the lymphatic system. They damage vessels and glands. After years of infestation, arms, legs, and scrotum swell and distort. elephantiasis, Figure 26: Elephantiasis. © John Greim/Photo Researchers, Inc.

Arthropods as Vectors Kingdom: Animalia Phylum: Arthropoda (exoskeleton, jointed legs) Class: Insecta (6 legs) Lice, fleas, mosquitoes Class: Arachnida (8 legs) Mites and ticks May transmit diseases (vectors) Figure 12.31, 32

Arthropod Vectors Figure 23.24

Arachnids Adult arachnids have four pairs of legs Ticks and mites resemble each other morphologically Ticks are the most important arachnid vectors Serve as vectors for bacterial, viral, and protozoan diseases Second only to mosquitoes in the number of diseases they transmit Transmit Lyme disease, Rocky Mountain spotted fever, tularemia, relapsing fever, and tick-borne encephalitis Parasitic mites are found wherever humans and animals coexist Transmit rickettsial diseases among animals and humans

Insects Adults have three pairs of legs as well as a head, thorax, and abdomen Fleas Most fleas are not associated with humans but a few do feed on humans Bubonic Plague is the most significant disease transmitted by fleas. Killed ½ of Europe in middle ages Body lice Parasites that can also transmit disease Most common among poor or overcrowded communities

Insects Flies Among the most common insects Those that transmit disease are generally bloodsuckers Mosquitoes Most important arthropod vector of disease Carry some of the world’s most devastating diseases

Eukaryotic Microbes Table 12.1