Parasitic Diseases Protozoan and helminthic parasites exist worldwide Common among people in rural, undeveloped, or overcrowded places Emerging as serious threats in developed nations Parasitic infections often involve several hosts Definitive host Intermediate host Parasites can infect humans in several ways

Routes by which humans acquire parasitic infections Figure 23.1

Protozoan Parasites of Humans Protozoa (single-celled eukaryotes) that enter the body via ingestion Most do not cause disease and are free-living in water Disease-causing ones include amoebas, giardia, plasmodium, etc…

Protozoan Parasites of Humans Amoebae Entamoeba hystolytica Causes amoebic dysentery About 50 million people worldwide are affected Carried asymptomatically in the digestive tracts of humans No animal reservoir exists Infection occurs most often by drinking water contaminated with feces containing cysts; can be transmitted through contaminated food

Entamoeba…. Symptoms: -abdominal pain, diarrhea, fatigue, fever, vomiting, bloody stool, weight loss Treatment: Oral antiparasitic medication, surgery may be necessary to treat complications like liver abscess or perforated bowel Prevention: Filtering drinking water or adding iodine or boiling; washing fruits and vegetables with clean water or peeling them

Entamoeba histolytica Figure 23.2

Protozoan Parasites of Humans Trypanosoma cruzi Causes Chagas’ disease Endemic in Central and South America Opossums and armadillos are the primary reservoir Transmission occurs through bite of insects in genus Triatoma “Kissing bugs” feed preferentially from blood vessels in the lips

Trypanasoma cruzi Figure 23.4

Protozoan Parasites of Humans Chagas’ disease Progresses through four stages Acute stage characterized by chagomas Generalized stage An asymptomatic chronic stage Symptomatic stage characterized by congestive heart failure following formation of pseudocysts Parasite-induced heart disease is a leading cause of death in Latin America

The life cycle of Trypanasoma cruzi Figure 23.3

Protozoan Parasites of Humans Trypanosoma brucei Causes African sleeping sickness The insect vector is the tsetse fly Humans usually infected when bitten by infected tsetse flies Site of the fly bite becomes a lesion with dead tissue Fever, lymph node swelling, and headaches Meningoencephalitis (inflammation of the central nervous system) Treatment – antiparasitic medication Prevention – DEET repellant, medium-weight long-sleeved shirts and pants in neutral colours

The parasite….causing sleeping sickness

The life cycle of T. brucei Figure 23.5

Protozoan Parasites of Humans Leishmania Causes leishmaniasis, transmitted by sand fly bites Endemic in parts of the tropics and subtropics Wild and domestic dogs and small rodents are common hosts 2 million new cases yearly around the world Symptoms: * weight loss, low blood count, fever, dark skin pigmentation, renal failure, skin ulcers, etc. Treatment – medication Prevention – prevention of being bitten

The life cycle of Leishmania Figure 23.6

Leishmaniasis vector - sand fly

Mucocutaneous leishmaniasis Figure 23.7

Protozoan Parasites of Humans Giardia intestinalis Found in intestinal tracts of animals and in the environment Causative agent of giardiasis Common gastrointestinal disease in the United States Ingest cysts in contaminated water or when swimming Range from asymptomatic infection to gastrointestinal disease The parasite multiplies in the small intestines Symptoms: diarrhea, abdominal cramps, vomiting, fever Prevention: use of filtered water

Giardia intestinalis Figure 23.8

Protozoan Parasites of Humans Malaria Plasmodium Causative agent of malaria Around 216 million cases of malaria worldwide; 655,000 deaths (91%) in Africa (2010 figures) Four species cause malaria P. falciparum, P. vivax, P. ovale, and P. malariae Malaria is endemic throughout the tropics and subtropics Mosquitoes (Anapholes) are vector for Plasmodium The Plasmodium life cycle has three prominent stages

The life cycle of Plasmodium Figure 23.11

Geographical distribution and incidence of malaria Figure 23.10

Plasmodium falciparum in erythrocytes (red blood cell) Figure 23.12

Protozoan Parasites of Humans Plasmodium Some genetic traits increase malaria resistance in endemic areas Sickle-cell trait Sickle-shaped cells resist penetration by Plasmodium Hemoglobin C Two genes for hemoglobin C protect against malaria

Protozoan Parasites of Humans Malaria Symptoms of malaria depend on cycle of parasite: High fever, joint pain, vomiting, weakness, renal failure, confusion, seizures Cerebral malaria results in tissue death in the brain (P. falciparum) Immunity develops if victim survives acute stage Periodic episodes become less severe over time

Malaria Treatment - Various antimalarial medication – type depends on severity of case Prevention Avoid getting bitten Use anti-malaria medication (prophylaxis) – chloroquine, mefloquine, primaquine

Protozoan Parasites of Humans Toxoplasma T. gondii is causative agent of toxoplasmosis One of the world’s most widely distributed parasites Wild and domestic mammals and birds are major reservoir Cats are the definitive host Infection due to consumption of undercooked meat containing the parasite Ingestion or inhalation of contaminated soil can also occur; can cross the placenta

The life cycle of Toxoplasma gondii Figure 23.13

Protozoan Parasites of Humans Toxoplasmosis Most infections are asymptomatic Toxoplasmosis develops in a small number of people Fever-producing illness combined with other symptoms Usually is a self-limited infection Toxoplasmosis is more severe in two populations AIDS patients Fetuses Prevent by cooking meats and avoiding contaminated soil

Toxoplasma gondii Figure 23.14

Protozoan Parasites of Humans Cryptosporidium parvum Causative agent of cryptosporidiosis (Cryptosporidum enteritis) Once thought to only infect livestock and poultry Humans can carry the parasite asymptomatically Infection usually results from drinking contaminated water Fecal-oral transmission can occur Causes severe diarrhea that can last up to two weeks Chronic Cryptosporidum enteritis indicator a person has AIDS Infection of AIDS patients can be life threatening

Cryptosporidiosis Symptoms: Abdominal cramping, diarrhea, malaise, malnutrition and weight loss (severe cases), nausea Treatment: Various treatments including nitazoxanide, atavaquone, paromomycin, etc.. Complications: In healthy people, then it just clears up. If you immunosuppressed, you could suffer from pancreatitis, inflammation of the bile duct and gallbladder…etc.

Oocysts of Cryptosporidium parvum Figure 23.15

Helminthic Parasites of Humans Helminths are macroscopic, multicellular, eukaryotic worms Life cycles are complex Intermediate hosts are often needed to support larval stages Three groups of helminthes Cestodes (tapeworm) Trematodes (fluke) Nematodes (roundworm)

Helminthic Parasites of Humans Tapeworms

Generalized life cycle of some tapeworms of humans Figure 23.17

Helminthic Parasites of Humans Blood flukes: Schistosoma Causative agent of schistosomiasis (bilharzia) Humans are the principal host, but snails are also hosts The worms burrow through skin of humans who contact contaminated water Larvae mature and mate in the circulatory system Eggs move to the intestines or the urinary bladder and ureters Dermatitis may occur at the site where cercariae entered Infections can become chronic and can be fatal Prevention relies on improved sanitation and avoiding contaminated water

Schistosoma mansoni Figure 23.21

Ascaris lumbricoides Figure 23.22

Mouth of Ancylostoma duodenale Figure 23.23

Eggs of Enterobius vermicularis Figure 23.24

Elephantiasis in a leg Figure 23.26

A microfilaria of Wuchereria bancrofti in blood Figure 23.25