Dr. Stan Eisen

Biology Department

Christian Brothers University

650 East Parkway South

Memphis, TN 38104

@2000

 Professional Societies:

Journal: Journal of Parasitology

Journal: American Journal of Tropical Medicine and Hygiene

Home page for the journal Molecular and Biochemical Parasitology

World Health Organization Web Page (Contains WHO documents on tropical health)

 Directory of Parasitologists: Lists scientists working in the field

URL <ftp://magnus.acs.ohio-state.edu/pub/zoology>

Parasite Genome Projects: Provides descriptions of projects and links to other genome projects

Newsgroups for parasitology-related areas, including bionet.parasitology, bionet.molbio, and bionet.protista

HELMINTH INFECTIONS IN HUMANS.(ADAPTED FROM PETERS AND GILLES, 1977 AND PETERS, 1978)

PROTOZOAN INFECTIONS IN HUMANS (From Markell & Voge: Medical Parasitology)

PARASITE: An organism which derives sustenance or benefit at the expense of its host.

• ENDOPARASITE = internal
• ECTOPARASITE = external
• OBLIGATE: Parasite stage necessary for completion of life cycle. e.g., Trichuris trichiura, Entamoeba histolytica.
• FACULTATIVE: Normally free-living, but can exist as a parasite, e.g., Strongyloides stercoralis.
• ACCIDENTAL: A parasite found in an abnormal host, e.g., Naegleria fowleri.

HOST: That organism which is necessary for the development of a parasite.

• DEFINITIVE: Parasite reaches sexual maturity, e.g., Humans for Clonorchis sinensis
• INTERMEDIATE: Necessary for development, but parasite does not reach sexual maturity, e.g., cyprinid fishes for Clonorchis sinensis
• PARATENIC: A host which is not necessary for the physiological development of the parasite, but which facilitates transferral from the intermediate host to the definitive host to the definitive host.
• VECTOR: Any agent, e.g. an arthropod, that transmits a disease organism.

HYPERPARASITISM: Parasite serving as a host for another parasitic species.

SPECIALIZED TERMS FOR PROTOZOA:

TROPHOZOITE: Metabolically active form of protozoan parasites,
within the appropriate organ of the host.

CYST: Metabolically inactive form of protozoan parasites,
adapted for transmission.

I. SPECIALIZATION

• Certain sensory organs are highly developed.
• Resistant stage (e.g. cyst or egg) for transferral to new hosts.

 II. DEGENERATION

• "Unnecessary" organs become vestigial or disappear.
• Loss of capacity to synthesize enzymes, nutrients.

 III. HIGH BIOTIC POTENTIAL, facilitated by

• Hermaphroditism: Adults have functional male and female reproductive systems. In parasitic organisms, this hermaphroditism is simultaneous, as opposed to sequential.
• Parthenogenesis: Development of an egg without fertilization by a sperm cell. Common among insects, e.g. aphids.
• Polyembryony: Larval forms undergo a form of budding in the intermediate host. This is observed in digenetic trematodes (flukes) and some wasps.
• Strobilization: Segments (proglottids) develop behind a holdfast organ (scolex). Each proglottid develops within it complete male and female reproductive systems. Following self- or cross-fertilization, the male reproductive structures deteriorate and eggs mature mature. Proglottids which are furthest away from the scolex are gravid, and will release eggs when the proglottid is shed.

 SIX ESSENTIAL ASPECTS TO A PARASITE LIFE CYCLE

 1. Find a Host

• Active: Host produces either chemical, thermal or light signals to which the infective stage is sensitive.
• Passive: Infective stages are dispersed passively through environment, such as waves or water currents.

 2. Enter a Host

• Active: Infective stage may burrow into skin, as cercariae of blood flukes do.
• Passive: Host will ingest or inhale infective forms.

 3. Overcome Host Defenses: Mechanisms include

• Antigen Shielding: Surface of parasite adsorbs host derived antigen, so that parasite is recognized as "self". (Documented among adult blood flukes)
• Surface Antigen Shifting: Proteins forming protein surface change so that immune reactions lag behind development of the parasites. (Documented in Trypanosoma gambiense and T. rhodesiense (African trypanosomiasis.)

 4. Derive Nutrients From Host

• Aerobic Metabolism
• Obligate Anaerobic Metabolism

5. Reproduce More Individuals

• Hermaphroditism
• Polyembrony
• Very high egg output: among some tapeworms, daily output can be in millions.

6. Disperse Young to New Hosts

• Presence of Obligate Free-living Stage: Needs to tolerate changes in temperature, osmotic pressure, desiccation.
• Passive or Active Dispersal: Cercariae of digenetic trematodes burrow out of snail host in search of 2^nd intermediate host or of definitive host.
• Parasite-Induced Change in Host Behavior: Intermediate stages will induce qualitative changes in the intermediate host such that the infected intermediate host is more likely to be captured by a predator which is the definitive host.

DIAGNOSTIC METHODS

 I. IMMIGRANTS

 Malaria, Amoebiasis, Schistosomiasis, Clonorchiasis

 II. TOURISTS & SERVICEMEN (NOT NECESSARILY OVERSEAS)

 Same As Above Plus Giardiasis

 III. CHILDREN

Enterobius (Pinworm), Hydatid Cyst (Echinococcus), Ascariasis, Trichuriasis, Hookworms, Lice, Toxoplasmosis, Dermal Larva Migrans, Visceral Larva Migrans, Naegleria/Acanthomoeba

IV. IMMUNOSUPPRESSED

 Pneumocystis, Toxoplasma, Strongyloides, Cryptosporidium

V. RURAL AND INDIGENT

 Trichinella, Strongyloides, Giardia, Entamoeba, Hookworms, Ascariasis

VI. PEOPLE WHOSE DIETS INCLUDE RAW MEATS

Trichinella (pork), Diphyllobothrium (freshwater fish), Anisakis (marine fish), Taenia (pork), Taeniarhynchus (beef)

VIII. PROMISCUOUS (through not necessarily)

Comparative morphology of the amebas of man and schematic representation of their nuclei. Adapted from Figure 3-1 and Table 3-1 of Brown & Neva (1983), Basic Clinical Parasitology, Appleton-Century-Crofts, Norwalk, Connecticut.

 Entamoeba histolytica (amebic dysentery)

Images:

Phylogeny:
Superclass Sarcodina

Preferred definitive host:
Humans

Reservoir hosts:
Dogs, Pigs, Monkeys

Vector/intermediate hosts:
None are necessary, but transport by filth flies is possible

 Geographical location: Cosmopolitan

Organs affected:
Coecum, appendix, colon. Advanced disease may include the liver and lungs.

Symptoms and clinical signs:
Mucosal destruction, perforated colons, peritonitis, abscesses in liver, lesions in lungs.

 Treatment:
Metronidazole, Dehydroemetine, Chloroquine

 Entamoeba coli

 Images:

Phylogeny:
Superclass Sarcodina

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate hosts:
None

Geographical location:
Cosmopolitan

Organs affected: Cecum and general colon

 Symptoms and clinical signs:
Symptomless, since E. coli feeds on bacteria, yeast, and on rare occasions, blood cells. This species is frequently mistaken for E. histolytica.

 Treatment: None required

Phylogeny:
Superclass Sarcodina

Preferred definitive host:
Humans

Reservoir hosts:
None, but it will infest primates, dogs, and cats. Transfer is possible among avid pet lovers.

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Surface of teeth and gums, gingival pockets near the base of the teeth, and sometimes in the crypts of the tonsils.

Symptoms and clinical signs:
None

Treatment:
None required

Images:

Phylogeny
Superclass Sarcodina

Preferred definite host:
Humans

Reservoir hosts:
None

Vector/Intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Lives in the large intestine, mainly at the level of the cecum and feeds on bacteria.

Symptoms and clinical signs:
None. This organism is a commensal which can be confused for pathogenic species

Treatment:
None required

Images:

Phylogeny:
Superclass Sarcodina

Preferred definitive host:
Humans

Reservoir hosts:
Other primates and pigs

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Large intestine, mainly in the cecal area

Symptoms and clinical signs:
Generally none, but in a few cases it has induced ectopic abscesses like those of E. histolytica.

 Treatment:
None required

Phylogeny:
Superclass Sarcodina

Preferred definitive host:
Humans are an accidental host for Naegleria.

 Reservoir hosts:
None

Vector/intermediate host:
None

Geographical location:
Cosmopolitan. Cases have been documented in Europe, North America, Africa, New Zealand, and Australia.

 Organs affected:
Brain tissue

Symptoms and clinical signs:
Meningoencephalitis, involving convulsions leading to death.

 Treatment:
None are available. Infection with Naegleria is always fatal.

 Giardia lamblia (intestinalis)

 Images:

Phylogeny:
Order Diplomonadida

Preferred definitive host:
Humans

Reservoir hosts:
Possibly dogs, cats, rodents, cattle, beaver

Vector/intermediate host:
None

Geographical location:
Cosmopolitan, but occurs most frequently in warm climates among children.

 Organ affected:
Duodenum, jejunum, and upper ileum.

Symptoms and clinical signs:
Mucus in stools, diarrhea, dehydration, intestinal pain, flatulence, and weight loss.

 Treatment:
Quinacrine, Metronidazole

 Images:

Phylogeny:
Order Retortamonadida

Preferred definitive host:
Humans

Reservoir hosts:
Other hosts include chimpanzees, orangutans, monkeys, and pigs

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Cecum and colon

Symptoms and clinical signs:
May cause watery stools

Treatment:
None required

Images:

Phylogeny:
Order Trichomonadida

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs Affected:
Vagina and urethra of women and in the prostate, seminal vesicles, and urethra of men

Symptoms and clinical signs:
Frequently symptomless among males,
but some strains cause inflammation, with itching and a copious white discharge swarming with trichomonads. Vaginal secretions may become greenish and condition may become chronic and/or recurrent.

Treatment:
Metronidazole

Images:

Phylogeny:
Order Kinetoplastida

Preferred definitive host:
Humans

Reservoir hosts:
Dogs, jackals, foxes

Intermediate/vector hosts:
Phlebotomus spp. sandflies

Geographical location:
Southern Russia, China, Northeast India, Bangladesh, Central and South America

 Organs affected:
Reticuloendothelial system

Symptoms:
Fever, anemia, edema, difficulty breathing,
diarrhea, emaciation, hepatosplenomegaly as compensation for anemia

Treatment:
Antimony sodium gluconate, Pentamidine

Images:

Phylogeny:
Order Kinetoplastida

Preferred definitive host:
Humans

Reservoir hosts:
Dogs, rodents

Intermediate/vector hosts:
Phlebotomus spp. sandflies

Geographical location:
West-Central Africa, Mediterranean region, India, South America, Central America, Ethiopia

Organs affected:
Reticuloendothelial system, skin

Symptoms:
Ulcers and sores on skin

Treatment:
Antimony sodium gluconate. Frequently self-healing with lasting immunity.

 Images:

Phylogeny:
Order Kinetoplastida

Preferred definitive host:
Humans

Reservoir hosts:
Dogs, rodents, cats, kinkajou

Intermediate/vector hosts:
Lutzomyia spp. sandflies

Geographical location:
Central and South America

Organs affected:
Nasal system and buccal mucosa

Symptoms:
Destruction of cartilaginous and soft tissue, ulceration of lips, palate, pharynx leading to deformity.

 Treatment:
Antimony sodium gluconate, Amphotericin B, cycloguanil pamoate

Trypanosoma gambiense and T. rhodesiense (African trypanosomiasis)

Images:

Phylogeny:
Order Kinetoplastida

Preferred definitive host:
Humans

Vector/intermediate host:
Tsetse flies (genus Glossina spp.)

Geographical location:
Central and East central Africa

Organs affected:
Blood, central nervous system.

Symptoms and clinical signs:
Lymph nodes swell, increasing apathy, mental dullness, tremor of the tongue, hands and trunk, anemia due to lysis of rbc's, somnambulism.

Treatment: Arsenic drugs, suramin, pentamidine, Berenil.

Trypanosoma cruzi (American trypanosomiasis - Chagas’ Disease)

Images:

Phylogeny:
Order Kinetoplastida

Preferred definitive hosts:
Humans

Reservoir hosts:
Dogs, cast, opossums, armadillos, wood rat

Intermediate/vector hosts:
Triatoma bugs in Uruguay, Chili, Argentina, Rhodnius prolixus in northern South America and Central America

Geographical location:
Central and South America

Organs affected:
Lymph node, nervous tissue, heart muscle

Symptoms and clinical signs:
Swelling of lymph nodes, progressive deterioration of nervous tissue, resulting in loss of strength, nervous disorders, heart failure, megaesophagus or megacolon

 Treatment:
No effective drug

Plasmodium spp., including P. falciparum, P. malariae, P. ovale, and P. vivax (malaria)

Images:

Phylogeny:
Subphylum Apicomplexa

Preferred definitive host:
Technically, mosquitos are the definitive host since the parasite undergoes sexual reproduction in the mosquito. By convention, mosquitos are considered the "vectors" to humans.

Reservoir hosts:
None

Vector/intermediate host:
Mosquitos, particularly those of the genus Anopheles.

Geographical location:
Central and South America, Africa, Middle East, Asia, Pacific Islands

Organs affected:
Liver, blood, kidney

Symptoms and clinical signs:
Most symptoms are associated with its effects on erythrocytes. Symptoms commonly include chills, fever, and anemia. Other symptoms include muscle pain, headache, loss of appetite, nausea, vomiting, jaundice, and renal failure.

Treatment: Chloroquine, Primaquine, Sulfamethoxine, Pyrimethamine, Sulfadiazine, Quinine, Amodiaquine.

CHARACTERISTICS OF PLASMODIUM SPP.

Images:

Phylogeny:
Subphylum Apicomplexa

Preferred definitive host:
Domestic cats, Puma, Ocelot, bobcat, Jaguarundi

Reservoir hosts:Technically none, but cockroaches, flies and leeches serve as transport hosts.

Vector/intermediate host: Humans, Domestic animals such as sheep, wild animals such as sheep, insectivores, rodents, pigs, herbivores.

 Geographical location:
Cosmopolitan

Organs affected:
Lymph glands, lung, liver, heart, brain, eyes. Toxoplasma can pass through the placental barrier and affect the developing fetus.

 Symptoms and clinical signs:
Among adult humans, it can cause fever, headache, muscle pain, anemia, spastic paralysis, blindness, myocarditis, permanent heart damage. Infection among pregnant women may cause stillbirths or spontaneous abortions. Congenital conditions include hydrocephalus, microcephaly, cerebral calcification, chorioretinitis and psychomotor disturbances.

Treatment:
Pyrimethamine with trisulfapyrimidines.

Images:

Phylogeny:
Uncertain (Ribosomal RNA analysis suggests affinity to Fungi)

Preferred definitive host:
Apparently none. It is a saprophyte found in the lungs of many species of animals.
 

Reservoir hosts:
None

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Lungs

Symptoms and clinical signs:
This organism causes interstitial pneumonia among immunosuppressed individuals. Among children, it may cause sever dyspnea, tachypnea, cyanosis, and instant death. Among adults, it may cause a dry, hacking cough, cyanosis, and dyspnea. Mild cases may show minimal alveolar septal infiltration with lymphocytes and occasional plasma cells, but sever cases may show widespread interstitial and alveolar edema,. with lymphocytic and plasma cell infiltration, necrosis of alveolar walls, and masses of P. carinii in the alveoli.

Treatment:
Pentamidine isethionate, Trimethroprim and sulfamethoxazole.

Cryptosporidium spp.

Images:

Phylogeny:
Phylum Apicomplexa

Preferred definitive host:
Difficult to determine since there are 10 named species among humans, birds, and other mammals.

Reservoir hosts:
Oocysts taken from an immunodeficient person were used to infect kittens, puppies and goats.

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Small intestine

Symptoms and clinical signs:
Among immunocompetent individuals, it causes a self-limiting diarrhea and abdominal cramps lasting 1 to 10 days. However, it causes a profuse, watery diarrhea among immunosuppressed (AIDS) which can persist for months and be life-threatening.

Treatment:
No effective drug treatment has been found yet.

Images:

Phylogeny:
Phylum Ciliophora

Preferred definitive host:
Humans

Reservoir hosts:
Pigs, guinea pigs, rats, other mammals.

Intermediate/vector hosts:
None

Geographical location:
Most common in Philippines, but is cosmopolitan

Organs affected:
Cecum and colon

Symptoms:
Proteolytic enzymes digest the intestinal epithelium of the host. Ulcer is flask-shaped, and causes lymphocytic infiltration, hemorrhage, secondary bacterial infection. Large intestine and appendix may be perforated.

 Treatment:
Carbarsone, diiodohydroxyquin, tetracycline. Epidemiological control and treatment are similar to those of E. histolytica.

Clonorchis sinensis (Chinese liver fluke)

 Images:

 PHYLOGENY:
Subclass Digenea, Order Opisthorchiata

Preferred definitive host:
Humans

Reservoir hosts:
Dogs and cats are probably most important. Others may include pigs, rats, and camels.

Vector/intermediate host:
#1. Snail-Genus Parafossarulus manchouricus: #2. Fish-mostly cyprinids.

Geographical location:
Japan, Korea, Taiwan, Vietnam

Organs affected:
Bile duct and liver

Symptoms and clinical signs:
Erosion of epithelial lining and fibrosis of the liver occur. Symptoms include ascites, bile retention, gallstone formation, indigestion, diarrhea, and hepatomegaly.

Treatment:
Praziquantel.

Fasciola hepatica (Sheep liver fluke)

Images:

Phylogeny:
Subclass Digenea, Order Echinostomata

Preferred definitive host:
Sheep and cattle, rarely among humans

Reservoir hosts:
Sheep, cattle, rabbits

Vector/intermediate hosts:
#1. Snails – Fossaria modicella or Stagnicola bulimoides; #2. Metacercariae encyst on vegetation.

Geographical location:
Cosmopolitan. Human cases documented in Central & South America, Africa, Asia and Europe

Organs affected:
Biliary ducts, liver.

Symptoms:
Necrosis of liver occurs because of migration through the liver. Anemia can result in heavy infections. Worms in bile ducts cause inflammation and edema, leading to fibrous tissue forming in walls of the ducts. Back pressure causes atrophy of liver parenchyma, thus leading to cirrhosis and jaundice. Ectopic infections occur in eye, brain, skin and lungs.

Treatment:
Rafoxanide, praziquantel

Images:

Phylogeny:
Subclass Digenea, Order Echinostomata

Preferred definitive host:
Humans

Reservoir hosts:
Pigs

Vector/intermediate host:
Snails, genera Segmentina or Hippeutis

Geographical location:
China and Southeast Asia

Organs affected:
Small intestine

Symptoms and clinical signs:
Blockage of passageway will cause ulceration, hemorrhage, abscesses, hepatic fibrosis, and verminous intoxication.

Treatment:
Praziquantel

Paragonimus westermani (Chinese lung fluke)

Images:

Phylogeny:
Subclass Digenea, Order Plagiorchiata

Preferred definitive host:
Carnivores (e.g. felids, canids, viverids, and mustelids), rodents, and pigs.

Reservoir hosts:
Humans

Vector/intermediate hosts:
1. Snail of Family Thieridae; 2. Crab-Eriocheir japonicus.

Geographical location:
Japan, Korea, Taiwan, Western Africa, South America

Organs affected:
Mainly the bronchioles of the lungs, but the worms may wander into the brain or mesentery.

Symptoms and clinical signs:
Victim suffers from breathing difficulties and chronic cough. Worm is often fatal due to penetration of the brain, spinal cord, or heart.

Treatment:
Bithionol, Praziquantel

 Images:

Phylogeny:
Subclass Digenea, Order Strigeata

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
Snails-Genus Bulinus or Genus Physopsis

Geographical location:
Africa and the Middle East

Organs affected:
Adults reside in the venules of the urinary bladder.

Symptoms and clinical signs:
Initial phase involves abdominal pain, bronchitis, enlargement of the spleen and liver, and diarrhea. Hematuria and pain on urination follow. Because of cellular damage to urinary bladder, malignant tumors may form. Kidneys themselves are sometimes damaged.

Treatment:
Metrifonate, Preziquantel, Niridazole.

Images:

Phylogeny:
Subclass Digenea, Order Strigeata

Preferred definitive host:
Humans

Reservoir hosts:
Certain monkeys and rodents

Vector/intermediate host:
Snails-Genus Biomphalaria

Geographical location:
Northern Africa, Middle East, S. America

Organs affected:
Adults reside in the portal veins of the large intestine

Symptoms and clinical signs:
Initial phase involves abdominal pain, bronchitis, enlargement of the spleen and liver, and diarrhea. Egg deposition in venules of large intestine induces pseudotubercle formation, resulting in necrosis and ulceration. Cirrhosis and portal hypertension develop as liver becomes damaged. Splenomegaly occurs. Pseudotubercles may develop in the lungs or nervous system.

Treatment:
Oxamniquine, Praziquantel, Niridazole.

Images:

Phylogeny:
Subclass Digenea, Order Strigeata

Preferred definitive host:
Humans

Reservoir hosts:
Rats, dogs, cats, horses, swine, and deer.

Vector/intermediate host:
Snails-Genus Onchomelania

Geographical location:
Japan, China, Taiwan, Philippines, Indonesia.

Organs affected:
Adults reside in veins of the small intestine.

Symptoms and clinical signs:
Initial phase involves abdominal pain, bronchitis, enlargement of the spleen and liver, and diarrhea. Fibrous nodules containing eggs accumulate on serosal and peritoneal surfaces of the small intestine. Splenomegaly occurs. Cirrhosis and portal hypertension due to live damage follow. Neurological disorders, such as coma or paralysis, may occur due to egg deposition in the brain.

Treatment:
Praziquantel

GENERALIZED LIFE CYCLES: CESTODES

(Inner loop = cyclophyllidean pathway)

(Outer loop = pseudophyllidean pathway)

Hermaphroditic Adults

in Small Intestine

Eggs Passed in

Feces

1st Intermediate

Host Ingested

By Definitive Host

Cysticercoid or

Cysticercus Larva in

1st Intermediate Host

(as in Taenia spp.,

Cyclophyllidea)

2nd Intermediate

Host Ingested By

Definitive Host

Procercoid Larva

in 1st Intermediate

Host, (as in

Diphyllobothrium

latum

Pseudophyllidea)

Pleroceroid Larva in

2nd Intermediate Host

Diphyllbothrium latum (broad tapeworm)

Images:

Ovum, scolex, proglottids

Phylogeny:
Class Cestoda, Order Pseudophyllidea

Preferred definitive host:
Humans

Reservoir hosts:
Piscivorous mammals such as bears

Vector/intermediate host:
1. Diaptomus copepods; 2. Fish, particularly whitefish

Geographical location:
Scandinavia, Russia, Arctic, United States

Organs affected:
Small intestine

Symptoms and clinical signs:
Vague abdominal discomfort. Sometimes pernicious anemia due to vitamin B12 requirement of the parasite. Nausea and diarrhea sometimes occur, but these symptoms are rare.

Treatment:
Niclosamide, Quinacrine, Paromomycin

Taenia solium (pork tapeworm)

Images:

Phylogeny:
Class Cestoda, Order Cyclophyllidea

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
Pigs

Geographical location:
Cosmopolitan

Organs affected:
Adults reside in the small intestine. Cysticerci can reside in heart muscle, brain tissue, or inside the eye.

Symptoms and clinical signs:
Usually none among adults. Abdominal pain, dizziness, nausea, and diarrhea occur, but are relatively rare. Cysticerci, however, may cause irreparable damage to the eye or heart, may cause necrosis of heart tissue, and may cause severe damage to the central nervous system, leading to epilepsy and hydrocephalus.

Treatment:
For adults, niclosamide, quinacrine, or paromomycin. For cysticerci larvae, surgery is required.

Taeniarhynchus saginata (beef tapeworm)

Images:

Phylogeny:
Class Cestoda, Order Cyclophyllidea

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
Cattle

Geographical location:
Worldwide, but common in Africa and South America.

Organs affected:
Small intestine

Symptoms and clinical Signs:
Usually none, but abdominal pain, headache, diarrhea, and intestinal obstruction may occur in heavy infection.

Treatment:
Niclosamide, quinacrine, paromomycin.

Hymenolepis diminuta (rat tapeworm)

Images:

Phylogeny:
Class Cestoda, Order Cyclophyllidea

Preferred definitive host:
Rats

Reservoir hosts:
Humans, particularly children.

Vector/intermediate host:
Tribolium and/or Tenebrio beetles

Geographical location:
Cosmopolitan

Organs affected:
Small intestine

Symptoms and clinical signs:
Usually none

Treatment:
Niclosamide or paromomycin

Vampirolepis nana (small rat tapeworm)

Images:

Phylogeny:
Class Cestoda, Order Cyclophyllidea

Preferred definitive host:
Rats and mice

Reservoir hosts:
Humans, particularly children.

Vector/intermediate host:
OPTIONAL - Grain beetles, such as Tribolium or Tenebrio

Geographical location:
Cosmopolitan

Organs affected:
Small intestine

Symptoms and clinical signs:
Usually none

Treatment:
Niclosamide or paromomycin

Dipylidium caninum (dog tapeworm)

Images:

 Phylogeny:
Class Cestoda Order Cyclophyllidea

Preferred definitive host:
Domestic dogs and cats

Reservoir hosts:
Humans, particularly children

Vector/intermediate host:
Fleas

Geographical location:
Cosmopolitan

Organs affected:
Small intestine

Symptoms and clinical signs:
Usually none, although abdominal pain, headache, diarrhea, and verminous intoxication may occur, particularly in patients with heavy infection.

Treatment:
Niclosamide, quinacrine, or praziquantel.

Images:

Phylogeny:
Class Cestoda, Order Cyclophyllidea

Preferred definitive host:
Carnivores, particularly dogs

Reservoir hosts:
Other mammals

Vector/intermediate host:
Herbivores, particularly moose, reindeer, goats, camels and sheep. Humans are 'accidental' hosts.

Geographical location:
Cosmopolitan

Organs affected:
Cysts may develop in bone marrow, nervous system, liver, and lungs.

Symptoms and clinical signs:
Specific symptoms depend on the site of cyst formation. In general, the presence of the cyst will induce pressure in organs and cause necrosis. Hydatid fluid can induce anaphylactic shock and death.

Treatment:
Surgical removal of the cyst is required.

Trichuris trichiura (whipworm)

Images:

Phylogeny
Order Trichurata.

Preferred Definitive host:
Humans

Reservoir hosts:
Reported in monkeys and dogs.

Vector/intermediate host:
None

Geographical location:
Cosmopolitan, but most frequent in tropical countries

Organs affected:
Human cecum, appendix, ileum.

Symptoms and clinical signs:
In heavy infections, patients show small blood-streaked diarrheal stools, abdominal pain and tenderness, nausea and vomiting, anemia and weight loss. Prolapse of the rectum has occurred in some cases.

Treatment:
Mebendazole.

Images:

Phylogeny:
Order Trichurata

Preferred definitive host:
Humans

Reservoir hosts:
Carnivorous mammals, including rodents and pigs.

Vector/intermediate host:
None

Geographical location:
Cosmopolitan, but most frequently found in circumboreal countries.

Organs affected:
1. Initial phase - Mucosa of small intestine
2. Penetration phase - larvae lodging in striated muscle, myocardium, brain and meninges.

Symptoms and clinical signs:
1. Initial phase - Nausea, vomiting, diarrhea, headache
2. Penetration phase - Edema, conjunctivitis, fever, chills, dyspnea, muscle paint. Other symptoms include EKG disorders, headache, mental apathy, delirium, coma.

Treatment:
Symptoms are relieved with analgesics and corticosteroids. Thiabendazole is effective among experimental animals.

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Phylogeny:
Order Rhabditata

Preferred definitive host:
Humans

Reservoir hosts:
Other primates, dogs, cats, other mammals

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Adult worms are generally found in the small intestine. Occasionally, they will also be found the respiratory, biliary, or pancreatic system.

Symptoms and clinical signs:
I. Invasion phase - Penetration of the skin by larvae will cause slight hemorrhage and swelling. The site of entry will show intense itching. Worms may also enter the body orally by ingestion with contaminated food. Worms which follow the oral route bypass the pulmonary phase.

II. Pulmonary phase - Damage to lung tissue causes massive-host cell reactions. Symptoms include a burning sensation in the chest, nonproductive cough, bronchial pneumonia.

III. Intestinal phase - Among immunocompetent
individuals, the infection is generally asymptomatic. Among immunosuppressed individuals, the problems arising from hyperinfection can become life-threatening. There is persistent diarrhea, and migrating worms are known to transport coliform bacteria throughout the body, and thereby may cause a gram-negative encephalitis by entry into the nervous system.

Treatment:
Thiabendazole, Cambendazole.

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Phylogeny:
Phylum Nematoda, Order Strongylata

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Larvae affect the skin and lungs, while the adults affect the small intestine.

Symptoms and clinical signs:
1. Cutaneous phase: Itching of skin
2. Pulmonary phase: Bronchitis, pneumonitis
3. Intestinal phase: None in light infection. In heavy infections, anemia leading to dyspnea on exertion, weakness and dizziness occur. Heart shows atrophy, and children may show physical, mental, or sexual retardation. 

Treatment:
Mebendazole, pyrantel pamoate and supplemental iron to offset anemia.

Images:

Phylogeny:
Phylum Nematoda, Order Strongylata

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs Affected:
Larvae affect the skin and lungs, while the adults affect the small intestine

Symptoms and clinical signs:
1. Cutaneous phase: Itching of skin
2. Pulmonary phase: Bronchitis, pneumonitis.
3. Intestinal phase: None in light infection. In heavy infections, anemia leading to dyspnea on exertion, weakness and dizziness occur. Heart shows atrophy, and children may show physical, mental or sexual retardation.

Treatment:
Mebendazole, pyrantel pamoate and supplemental iron to offset anemia.

Comparison of Human Hookworms

Correlation between Necator worm burden and patient status 

ANCYLOSTOMA, TAKING MORE BLOOD PER DAY, WILL REQUIRE FEWER WORMS TO GENERATE SEVERE PATHOLOGY.

CHRONIC INFECTIONS LEAD TO MENTAL DULLNESS, PHYSICAL RETARDATION, HEART FAILURE, DEATH.

Ancylostoma caninum (dermal larva migrans)

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Phylogeny:
Phylum Nematoda, Order Strongylata

Preferred definitive host:
Domestic dogs and cats

Reservoir hosts:
None. Humans are 'accidental' hosts

Vector/intermediate hosts:
None

Geographical location:
Northern Hemisphere

Organs affected:
Skin

Symptoms and clinical signs:
Creeping eruption, characterized by inflammation and itching along migration pathways of larvae

Treatment:
Thiabendazole ointment.

Ascaris lumbricoides (large roundworm)

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Phylogeny:
Phylum Nematoda, Order Ascaridata

Preferred definitive host:
Humans

Reservoir hosts:
None, but Ascaris suum in swine is very similar

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Adults reside in the lumen of the small intestine

Symptoms and clinical signs:
1. Initial phase: Vague symptoms arising from inflammatory responses
2. Pulmonary phase: Edema, pneumonitis
3. Intestinal phase: Abdominal pain, asthma, insomnia. Use of ineffective drugs will stimulate migration, leading to serious and sometimes fatal results. Worms have been known to escape through the nares, and to penetrate the intestinal wall and emerge from the body wall. Worms will also invade visceral organs.

Treatment:
Piperazine citrate, mebendazole, pyrantel pamoate.

Toxocara cati and T. caninum (visceral larva migrans)

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Phylogeny:
Phylum Nematoda, Order Ascaridata

Preferred definitive host:
Cats and Dogs

Reservoir hosts:
None. Humans are 'accidental' hosts

Vector/intermediate host:
None

Geographical location:
Cosmopolitan

Organs affected:
Liver, lungs, eye, brain, cardiac muscle, kidney

Symptoms and clinical signs:
Visceral larva migrans results in inflammation and eosinophilic granulomas in organs. Pneumonitis, hepatomegaly, spleen enlargement, anemia, iritis and hemorrhage of the eye are common symptoms.

Treatment:
Thiabendazole

Enterobius vermicularis (pinworm)

Phylogeny:
Phylum Nematoda, Order Oxyurata

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
None

Geographical location:
Temperate zone, especially in Europe and North America

Organs affected:
Ileocecal region of the intestine

Symptoms and clinical signs:
Generally asymptomatic, but heavy infections will result in disturbed sleep. This, in turn, will debilitate the patient. Itching and pruritis are observed. Minute ulcerations of the intestinal mucosa and fatal subserosal penetration has been reported.

Treatment:
Piperazine citrate, pyrvinium pamoate, mebendazole.

LIFE CYCLE OF FILARIAL NEMATODES

Sexually Mature adults in

Lymph Vessels or Tissues

Larva develops Microfilariae in

in Tissues Blood

Insect Bites a Microfilariae

Subsequent Ingested by insect

Mammalian Host Intermediate

Host

Larvae undergo partial

Development in Insect

Host

Wuchereria bancrofti (elephantiasis)

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Phylogeny:
Phylum Nematoda, Order Filariata

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
Mosquitos, including the genera Anopheles, Aedes, Culex, and Mansonia

Geographical location:
Central Africa, Turkey, India, Southeast Asia, Australia, South Pacific Islands

Organs affected:
Microfilariae are in the blood, and adults reside in major lymphatic ducts.

Symptoms and Clinical signs:
Microfilariae are virtually symptomless. Inflammation caused by the presence of adults leads to chills, fever, and toxemia. Lymph vessels become swollen, leading to swelling of organs and the accumulation of lymph in urine.

Treatment:
Microfilariae and adults are killed by diethylcarbamazine. Mechanical damage is treated with pressure bandages or surgical removal of elephantoid tissue.

Onchocercus volvulus (river blindness)

Images:

Phylogeny:
Phylum Nematoda, Order Filariata

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
Simulium blackflies

Geographical location:
Africa, South and Central America

Organs affected:
Microfilariae are in skin, while adults reside in subcutaneous tissue.

Symptoms and Clinical signs:
Adults cause relatively minor problems. their presence lead to formation of subcutaneous nodules, but they are relatively benign and elicit no pain. Microfilariae cause dermatitis, skin lesions, depletion of vitamin A, and blindness due to corneal invasion.

Treatment:
Surgical removal of nodules, and administration of diethylcarbamazine and/or suramin.

Dirofilaria immitis (heartworm)

Images:

Phylogeny:
Phylum Nematoda, Order Filariata

Preferred definitive host:
Dogs

Reservoir hosts:
None. Humans are rare 'accidental' hosts. Cats are rarely infected.

Vector/immediate host:
Anopheline mosquitos

Geographical location:
Cosmopolitan

Organs affected:
Right heart and pulmonary artery

Symptoms and Clinical signs:
Microfilariae are virtually symptomless. However, the presence of a large number of adults will cause right heart failure and pulmonary complications in dogs. In humans, the symptoms are vague and unpredictable. It takes significantly less worms to elicit such symptoms in cats.

Treatment:
Adults are destroyed by thiacetarsamide sodium solution, and microfilariae are destroyed by the oral administration of dithiazamine iodide. Heartworm disease is prevented with diethylcarbamazine.

Dracunculus medinensis (Guinea worm)

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Phylogeny:
Phylum Nematoda, Order Camallanata

Preferred definitive host:
Humans

Reservoir hosts:
Other mammals

Vector/intermediate host:
Copepods, genus Cyclops

Geographical location:
Africa, Southwestern Asia, Northeastern South America, West Indies.

Organs affected:
Adults reside in subcutaneous tissues, especially in the legs, arms, shoulder and trunk.

Symptoms and Clinical signs:
Blister formation is accompanied by urticaria, erythema, dyspnea, vomiting, pruritus, all of which are of allergic nature. Severe inflammation may occur if worm is snapped.

Treatment:
Metronidazole, niridazole, thiabendazole.

 Limnatis SPP. (AQUATIC LEECHES)

 Phylogeny:
Phylum Annelida, Class Hirudinea

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
None

Geographical location:
Far East

Organs affected:
Primarily skin, but the worm is small enough that the respiratory and digestive systems will be affected. Bathers frequently have infections in the vagina, urethra or eyes.

Symptoms and clinical signs: Pain, hemorrhage

Treatment:
Removal of worms

Haemadipsa SPP. (terrestrial leech)

Phylogeny:
Phylum Annelida, Class Hirudinea

Preferred definitive host:
Humans

Reservoir hosts:
None

Vector/intermediate host:
None

Geographical location:
Far East

Organs affected:
Skin

Symptoms and clinical signs: Painless, unnoticed wounds on skin take a considerable time to clot due to anticoagulant used by leech to suck its blood meal.

Treatment:
Removal of worm by use of either a local anesthetic, a strong salt solution, or a lighted match. Repellents such as dimethyl phthalate are used on clothing.

CHARACTERISTICS OF MAJOR ANIMAL PHYLA

PHYLUM ACANTHOCEPHALA

2. Respiratory None. Exchange by Diffusion

MAJOR GROUPS

CLASS EOACANTHOCEPHALA

CLASS PALAEACANTHOCEPHALA

CLASS ARCHIANTHOCEPHALA

Images:

Phylogeny:
Phylum Acanthocephala

Preferred definitive host:
Hogs, wild boas, peccaries.

Reservoir hosts:
To a limited degree, cats and dogs serve as hosts. Humans are accidental hosts.

Vector/intermediate host:
Larval beetles

Geographical location:
Cosmopolitan. Human cases have been documented in Bohemia and Russia on the basis of ova discovered in the feces

Organs affected:
Intestine

Symptoms and clinical signs:
Abdominal pain

Treatment:
None indicated

Images:

Phylogeny:
Phylum Acanthocephala

Preferred definitive host:
Rats, mice, hamsters, dogs and cats

Reservoir hosts:
Humans are incidental hosts

Vector/intermediate host:
Beetles and cockroaches

Geographical location:
Cosmopolitan. Human cases have been reported from Italy, the Sudan, and British Honduras

Organ affected:
Small intestine

Symptoms and clinical signs: Abdominal pain, diarrhea, and exhaustion.

Treatment:
None indicated.