1. 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

2. Routes by which humans acquire parasitic infections
Figure 23.1

3. 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…

4. 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

5. 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

6. Entamoeba histolytica
Figure 23.2

7. 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

8. Trypanasoma cruzi
Figure 23.4

9. 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

10. The life cycle of Trypanasoma cruzi
Figure 23.3

11. 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

12. The parasite….causing sleeping sickness

13. The life cycle of T. brucei
Figure 23.5

15. 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

16. The life cycle of Leishmania
Figure 23.6

17. Leishmaniasis vector - sand fly

18. Mucocutaneous leishmaniasis
Figure 23.7

19. 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

20. Giardia intestinalis
Figure 23.8

21. 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

22. The life cycle of Plasmodium
Figure 23.11

23. Geographical distribution and incidence of malaria
Figure 23.10

24. Plasmodium falciparum in erythrocytes (red blood cell)
Figure 23.12

25. 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

26. 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

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

28. 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

29. The life cycle of Toxoplasma gondii
Figure 23.13

30. 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

31. Toxoplasma gondii
Figure 23.14

32. 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

33. 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.

34. Oocysts of Cryptosporidium parvum
Figure 23.15

35. 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)

36. Helminthic Parasites of Humans
Tapeworms

37. Generalized life cycle of some tapeworms of humans
Figure 23.17

38. 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

40. Schistosoma mansoni
Figure 23.21

41. Ascaris lumbricoides
Figure 23.22

42. Mouth of Ancylostoma duodenale
Figure 23.23

43. Eggs of Enterobius vermicularis
Figure 23.24

44. Elephantiasis in a leg
Figure 23.26

45. A microfilaria of Wuchereria bancrofti in blood
Figure 23.25