Copyright © 2011 Pearson Education Inc. Parasitic Diseases Protozoan and helminthic parasites exist...

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…

• 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

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

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

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 medicationPrevention – 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

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

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

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

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

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

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

ToxoplasmosisMost 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

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,

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)

• Tapeworms

Generalized life cycle of some tapeworms of humans

Figure 23.17

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

Copyright © 2011 Pearson Education Inc. Parasitic Diseases Protozoan and helminthic parasites exist...

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