Parasitic disease

1. An Overview of Parasitic Diseases
PARA-718 (Special Topics in Parasitology)

2. Introduction
• Parasitic diseases continue to be the major public health problems in
tropical developing countries
• According to WHO estimates the annual death toll due to parasitic
diseases is nearly 2.5 million throughout the world, e.g. malaria,
amoebiasis and hookworm infections
• Immunotherapy and vaccination may emerge as useful tools to
control and eradicate parasitic infections, but these are still in their
early stages of development
• Therefore, chemotherapy is the main tool available to combat
parasitic diseases in humans and domestic animals

3. • The pathogenic protozoans may invade the blood circulation, liver,
spleen, or external organs such as mouth, gastrointestinal tract and
vagina
• A major population of the helminths, on the other hand, parasitize
the gastrointestinal tract while some live in the blood circulation,
lymphatics, connective and subcutaneous tissues, eyes, lungs, and
liver
• The intestinal protozoal diseases are contracted by ingesting
protozoal cysts through food, drink and faecal contact

4. The Helminth Infections
• A variety of helminths belonging to the class nematoda
(roundworms), trematode (flatworms or flukes) and cestoda
(tapeworms) are known to infect humans and domestic animals
• The presence of helminth infections in livestock leads to decrease in
output of animal products and has, therefore, strong socio-economic
impact in countries with agro and dairy-based industries

5. Nematode Infections
Ascariasis: It is caused by Ascaris lumbricoides, the adult worms of
which live in the lumen of small intestine of man.
• The infection is acquired by consuming fruits, salad, vegetables and
drinks contaminated with Ascaris eggs.
• Ascariasis has a worldwide distribution affecting nearly 1000-1300
million people with nearly 20,000 patients dying every year.
• The main clinical manifestations of the disease during migration of
larvae from the gut to lungs are atypical pneumonia with
inflammation of lung and liver cells, fever and eosinophilia

6. • Hookworm infections: The hookworm disease is caused by the blood
sucking nematodes, Ancylostoma duodenale, A. ceylanicum and
Necator americanus, commonly known as hookworms, in the
intestine of human.
• The infection normally takes place when farmers working in coffee,
banana, sugarcane, sweet potato, rice and maize fields expose their
bare feet to the soil fertilized with human excreta where the infective
larvae penetrate the skin and enter the blood circulation.
• The most common clinical symptom of the disease is hypochromic
anaemia resulting from heavy blood loss.
• This leads to general weakness, fatigue, anorexia and poor health

7. • Trichuriasis: The disease is caused by Trichuris trichiura, commonly
known as whipworms, which live embedded in the intestine
especially in the large bowel and caecum of man
• The infection is cosmopolitan and is found more in children than
adults
• The usual mode of infection is the consumption of water and
vegetables contaminated with the ova of T. trichiura
• The disease is usually asymptomatic in the case of light infection;
however, heavy infections may lead to anaemia, eosinophilia,
abdominal pain, diarrhea, mucoid stool and occasional prolapse of
the rectum.

8. • Strongyloidiasis: Like hookworms, strongyloidiasis is also caused by
penetration of the human skin by filariform larvae of Strongyloides
stercoralis
• They live buried in the intestinal mucosa of human
• The clinical manifestations of the disease include attacks of diarrhea,
diffused abdominal pain, epigastric discomfort and hunger pains,
which may lead to false diagnosis of peptic ulcer
• Enterobiasis: It is a common helminth infection of man found mostly
in children and is caused by Enterobius vermicularis called pinworms

9. • Scratching of the perianal skin may lead to dermatitis, eczema and
secondary bacterial infections
• The patient may also suffer from anorexia, restlessness, insomnia and
mild to acute abdominal pain
• Trichostrongyloidiasis: Trichostrongylus orientalis is the main
etiological agent in humans
• The adult worms live embedded through their heads in the mucosa of
the duodenum and jejunum
• Human acquires the infection when the semi-filariform larvae of
Trichostrongylus species enter the body through skin or mouth

10. • Severe infections may give rise to mild anaemia as the worms may
suck blood with their capillary heads embedded in the mucosa
• Capillariasis: This is a relatively new enteric helminth disease of
human caused by a minute whipworm, Capillaria philippinensis
• The infection occurs when infected with fresh water fish and
crustaceans are eaten raw by man
• The infection causes a syndrome which resembles with that of auto-
infected and disseminated strongyloidiasis giving rise to abdominal
pain, vomiting, malaise, nausea and anorexia

11. • Intestinal angiostrongyliasis: The causative agents of the disease,
Angiostrongylus costaricensis and A. cantonensis, produce tumor-like
lesions in the colon
• Trichinosis: This is a disease caused by Trichinella spiralis which is
essentially a nematode parasite of rats
• The adult worms live in the small intestine of man
• Trichinosis is transmitted to humans, when they eat infected pork
• The presence of adult and larval parasites may give rise to abdominal
pain, nausea, vomiting, diarrhea and blood in stool

12. • Creeping eruption: Creeping eruption or larva migrans in man is
caused by the presence of the larvae of dog and cat hookworms,
Ancylostoma caninum and A. braziliense in the skin
• It is estimated that nearly 10 million people around the world suffer
from this disease
• Human acquires the infection by eating the above infected
intermediate hosts
• Visceral larva migrans: This form of tissue helminthiasis is caused by
the migration of the larvae of dog and cat ascarids, Toxocara canis
and Toxocara cati in the visceral tissues of humans

13. • Attacks of fever, malaise, nausea, vomiting, cough, abdominal pain,
anorexia, weight loss and muscle and joint pain may be observed
occasionally
• Filariasis: Filariasis is one of the most widespread parasitic diseases of
the tropics affecting nearly 300-400 million people around the world
• The main disease causing worms in humans are Wuchereria bancrofti,
Brugia malayi, Onchocerca volvulus, Loa loa, Dipetalonema perstans,
Dipetalonema streptocerca and Mansonella ozzardi
• The transmission of the infection to humans occurs when the
mosquitoes feed on the blood of man

14. • Tropical pulmonary eosinophilia (TPE): This is an allergic
manifestation produced by the presence of various helminth parasites
such as Ascaris lumbricoides, Trichinella spiralis, Strongyloides
stercoralis, Toxocara spp., Brugia malayi or Dirofilaria spp. in humans
• The disease has been reported from different parts of Asia and Africa

15. Trematode (flatworm, fluke) infections:
• Schistosomiasis: Schistosomiasis is a major helminth disease of man
caused by the invasion of the blood circulatory system by four species of
blood flukes, viz. Schistosoma haematobium, S. mansoni, S. japonicum and
S. intercalatum
• Schistosomiasis has a wide geographical distribution
• It has also been reported that S. mansoni infects nearly 70 million people
throughout the world
• Humans acquire schistosomiasis while working in rice fields, lakes, ponds,
canals and water streams where the cercariae present in the water

16. penetrate the skin and enter the blood stream
• The early phase of the disease is marked by Schistosoma dermatitis
and katayama fever (fever, chills, malaise)
• Fasciolopsiasis (intestinal fluke infections): Fasciolopsiasis in man is
acquired by eating raw stems, bulbs or fruits of some water plants
(water chestnut or water caltrop) infected heavily with the
matacercariae of Fasciolopsis buski
• The main clinical symptoms of the disease are abdominal pain and
diarrhea with nausea, vomiting and anorexia

17. • Liver fluke infections: The main liver flukes infecting man are Fasciola
hepatica, F. gigantica, Clonorchis sinensis, Opisthorchis felineus and
Dicrocoelium dendriticum
• Since the site of predilection of the liver flukes is liver or biliary passage,
the clinical manifestations produced by them chiefly relate to liver and
gastric problems.
• The early stage of the infection is marked by epigastric pain, fever and
eosinophilia
• Later the patient experiences diarrhea, anorexia, prolonged fever and
abdominal pain
• In chronic cases, the disease may lead to jaundice, cirrhosis of the liver and
biliary duct, ascites and cachexia

18. • Lung fluke infections: The most common lung fluke infecting man is
Paragonimus westermani
• Human acquires lung fluke infection by eating raw crabs and cray
fishes infected with metacercariae
• The main clinical manifestations of the disease are cough with
gelatinous blood, stained sputum and discomfort in the chest
• Mild anaemia, fever, body pain, adbominal pain and diarrhea with
occasional bloody mucus may also be observed

19. Cestode (tapeworm) infections
• Intestinal cestode infections: These are common parasitic infections
of the tropics resulting from the invasion of the gastrointestinal tract
of humans by Taenia saginata (beef tapeworm), Taenia solium (pork
tapeworm), Diphyllobothrium latum (fish tapeworm), Hymenolepis
nana (dwarf tapeworm), Echinococcus granulosus and E.
multilocularis
• The intestinal cestode infections have a world-wide distribution,
though they are more prevalent in the tropical and sub-tropical
regions

20. • The cestodes have a simple life cycle consisting of one or two hosts
• The clinical symptoms of the disease are nausea, vomiting, general
weakness, weight loss, abdominal pain and diarrhea
• Hydatid disease: This is one of the most serious tapeworm infections
caused by the hydatid cysts, formed by the larval stage of
Echinococcus granulosus and E. multilocularis in man and domestic
animals
• The disease is prevalent wherever man is closely associated with cats,
dogs and sheep. The adult worms live in the alimentary canal of the
definite host (cats, dogs, wolves, foxes and jackals)

21. • Humans acquire the infection by ingestion of Echinococcus eggs
through fruits, vegetables, salad or water
• The main pathological changes during hydatid disease is inflammation
and necrosis of tissues around the cysts
• The presence of hydatid cysts in liver causes nausea, vomiting, vague
abdominal pain and bulging of right hypochondrium or epigastrium
due to hepatic enlargement
• The patient may also exhibit biliary colic and jaundice

22. The Protozoal Infections
• A large number of protozoans are known to invade the
gastrointestinal tract, liver, spleen, brain, blood circulation and other
organs of humans and domestic animals producing a wide-spectrum
of morbidity and considerable mortality
• The important intestinal protozoal diseases of man are amoebiasis,
giardiasis, trichomoniasis, naegleriasis and toxoplasmosis
• Of these, amoebiasis is estimated to affect nearly 480 million people
around the world of which nearly 40,000-110,000 patient die every
year
• Giardiasis is another widespread disease infecting nearly 200 million
people around the globe

23. • The extraintestinal organs like liver, spleen, CNS and blood circulatory
system are also invaded by a number of parasitic protozoans through
the bites of a variety of mosquitoes, flies and bugs
• The major extraintestinal protozoal infections of man are malaria,
trypanosomiasis (Chaga's Disease and African sleeping sickness) and
leishmaniasis, all of which are notorious for their detrimental effects
on human health
• The clinical manifestations may range from fever and dermatological
problems to grave clinical complications involving CNS, liver and
tubular organs

24. • The presence of pathogenic protozoans in domestic animals also
produces debilitating effects and, therefore, eradication of these
parasites is essential for better health of livestock and improved
socio-economic status of the farmers
• The economic importance of protozoal infections may be judged by
the fact that more than US$ 280 million are spent worldwide in
poultry industry alone for prophylactic treatment of chicken against
coccidiosis
• It has been estimated that nearly 1.2 billion cattle in the world are
potentially exposed to the risk of babesiasis caused by different
species of Babesia

25. Intestinal protozoans
• Entamoeba histolytica: This is the most common intestinal parasite
responsible for causing amoebiasis in humans
• The disease has a cosmopolitan distribution, and is endemic in some parts
of the world
• Amoebiasis is marked by two phases of the infection:
• (a) intestinal amoebiasis characterised by dysentery and diarrhea,
nondysenteric colitis, amoeboma (amoebic granuloma) and amoebic
appendicitis; and
• (b) extraintestinal amoebiasis (hepatic amoebiasis) marked by liver abscess

26. • Trichomonas vaginalis: It is a pathogenic flagellate responsible for
causing vaginitis or urethritis in women and men, respectively, and
has world wide distribution
• Coitus is probably the main source of transmission of the infection
• Giardia lamblia: This is pathogenic flagellate which usually inhabits
the duodenum and upper jejunum but may also be found in the gall
bladder
• The clinical manifestations of the disease may include epigastric pain,
nausea, flatulence and diarrhea
• Acute giardiasis may be associated with steatorrhea and weight loss

27. • Balantidium coli: The infection is reported to occur throughout the
world producing diarrhea and dysentery
• Isospora spp. The pathogenic protozoans of this class are lsospora
belli and I. hominis which inhabit the small intestine of man
• The infection may give rise to abdominal pain, diarrhea, nausea,
anorexia and headache

28. Extra-intestinal protozoans
• Toxoplasma gondii: It is a widely distributed pathogenic parasite of
man and animals
• Cats serve as the definite host
• Man becomes infected by eating poorly cooked or raw meat of sheep,
pigs and cows containing toxoplasma cysts
• The disease appears in two forms: congenital and acquired

29. • Cryptosporidium spp. This is a mild type of pathogen
• Although the infections due to Cryptosporidium usually subside without
therapy, it may produce chronic debilitating diarrhea, especially in patients
with AIDS and low immunological profile
• Plasmodium spp. A number of species of Plasmodium invade the blood
and liver causing malaria in man and animals
• The important pathogens of malaria in man are Plasmodiunl falciparum, P.
vivax, P. ovale and P. malariae
• The disease is transmitted to man by female mosquitoes belonging to the
genus Anopheles and is endemic in several parts of Asia, Africa and South
America

30. • The main clinical manifestations of malaria are periodic fever with
chills, splenomegaly, anaemia and leukopenia
• The final stage of the disease is characterized by coma and death of
the patient
• Trypanosoma spp. Several haemoflagellates of the genus
Trypanosoma are known to invade the central nervous system, blood
and tissues causing acute and chronic protozoal diseases, collectively
termed as 'trypanosomiasis'.
• Chaga's disease or American trypanosomiasis is caused by the
invasion of the blood and tissues by the trypanosome T. cruzi

31. • The main victims of this disease are children and young adults
• The acute phase of the disease is marked by high fever, anorexia,
vomiting, diarrhea and enlargement of the liver and spleen
• Leishmania spp. A number of intracellular protozoan parasites
belonging to the genus Leishmania infect humans through female
sand flies of the genus Phlebotomus, Sergentomyia and Lutzomyia
• Depending upon the nature of infection, human leishmaniasis can be
• divided into three forms:
• (a) Visceral leishmaniasis (Kala-azar) and post kala-azar dermal
leishamaniasis (PKDL) caused by Leishmania donovani complex;

32. • (b) cutaneous leishmaniasis caused by L. tropica complex and L.
mexicana complex and,
• (c) mucocutaneous leishmaniasis due to L. brasiliensis