Comprehensive Nematodes and Tissue Parasites: Types, Life Cycles, and Pathology

Parasitology

The study of a parasite (organism 1) and its relationship to its host (organism 2)

Symbiosis

The living together in more or less intimate association or close union of two dissimilar organisms

Mutualism

An interaction between two or more species where each species has a net benefit (+,+)

Commensalism

An association between two organisms in which one benefits and the other derives neither benefit nor harm (+,0)

Parasitism

A relationship between species, where one organism, the parasite, lives on or in another organism, the host, causing it some harm, and is adapted structurally to this way of life (+,-)

Facultative Parasite

An organism that may resort to a parasitic lifestyle, however, it does not rely on a host for completion of its life cycle

Obligatory Parasite

A parasitic organism that cannot complete its life cycle without a relationship with a suitable host

Endo-parasite

A parasite that lives within a host and causes an infection

Ecto-parasite

A parasite that lives on a host and causes an infestation

Definitive Host

A host that supports the adults or sexually reproductive stage of a parasite. This stage is necessary for parasite survival

Intermediate Host

A host that supports the immature or non-sexual reproductive forms of a parasite. There may be asexual reproduction. This stage is necessary for parasite survival

Transfer Host

A host that can move or relocate parasite stages from one location to another; most often reproductive stages such as eggs

Vector

A host that acts as a definitive or intermediate host for a parasite, but more importantly transfers the parasite to the next host

Reservoir Host

A host that serves as a source of infection and potential reinfection of humans, and as a means of sustaining a parasite within a population and ecosystem

Biological Incubation Period

The period between exposure to an infection and the appearance of the first signs and symptoms

Exposure

Being in contact with an infectious organism

Colonization

The presence of an infectious agent (bacteria) in or on a body surface without causing disease in the person

Infection

The invasion and growth of infectious agent germs in or on the body

Sign

An objective evidence of a disease that can be observed by others

Symptom

Subjective evidence of a disease, that is, apparent only to the patient

Latency

The time from infection to infectiousness or being able to pass the infection

Infectivity

Ability of an organism to establish an infection

Invasiveness

Ability of an organism to spread to adjacent or distant tissues

Pathogenicity

Ability to produce substances that damage tissues

Lytic Necrosis

Digestion of tissue, e.g., Entamoeba hystolytica

Traumatic Damage

Mechanical damage to host tissue, e.g., Internal larval migrations

Obstruction of Lumens

Blockage of tubes within the body, e.g., Ascaris lumbricoides

Eosinophilia

Increased production of eosinophils, white blood cells, which are part of host defense against parasitic infections

Neoplasia

Uncontrolled proliferation of cells due to excessive parasite induced tissue damage and repair

Enterobius vermicularis

Pinworm; causes abnormal migrations and various clinical manifestations

Trichuris trichiura

Whipworm; causes tissue injury and necrosis in the large intestine

Ascaris lumbricoides

Giant Round Worm; can cause intestinal obstruction and abnormal migrations

Toxocara canis

Dog Roundworm; humans are not preferred hosts and infection occurs via foodborne transmission

Baylisascaris procyonis

Raccoon Roundworm; humans are not preferred hosts and larvae migrate through somatic tissue

Invasion of the visceral organs

Invasion of the visceral organs (VLM), central nervous system (NLM), or eyes (OLM) may occur.

Necator americanus

New world hookworm.

Ancylostoma duodenale

Old world hookworm.

Epidemiology of hookworms

Tropics, subtropics, and temperate zones; some mixing due to population migrations; temperature and rainfall important.

Larval Penetration Symptoms

Papule, vesicle, lesion, puritis (itching), edema (swelling), erythema (redness).

Repeated infections of hookworms

Can cause allergic reactions - hypersensitivity; ground itch.

Diagnosis of hookworm infection

Eggs in stool.

Treatment for hookworm infection

Albendazole or Mebendazole.

Reinfection rate of hookworms

Reinfection is up to 80% in 36 months.

Prevention of hookworm infection

Sanitation and disposal of feces, proper treatment of night soil, personal hygiene, shoes.

Ancylostoma caninum

Cutaneous Larval Migrans.

Infection from Ancylostoma caninum

Skin penetration causing 'Ground Itch' - larval penetration and cutaneous movement, but no maturity.

Diagnosis of Cutaneous Larval Migrans

Observation.

Treatment for Cutaneous Larval Migrans

Albendazole, Mebendazole, Ivermectin orally, or Thiabendazole cream.

Trichinella spiralis

Pork Worm.

Epidemiology of Trichinella spiralis

Maintenance cycle includes pig-pig, rat-rat, rat-pig, wild boar, bear.

Control infections of Trichinella spiralis

Freezing meat at 18F, cook at 310F for 35 min per pound.

Pathology of Trichinella spiralis

Necrosis and panmucosal inflammation begins at 72 hours and peaks at 8 days.

Stage 1 symptoms of Trichinella spiralis

Nausea, vomiting, diarrhea, fever.

Stage 2 symptoms of Trichinella spiralis

Bilateral ocular edema as eye muscles invaded; primary sign of invasion.

Diagnosis of Trichinella spiralis

History of eating pork, ocular edema, muscle biopsy, serology.

Treatment for Trichinella spiralis

Supportive treatment and anti-inflammatory drugs; early treatment with albendazole or mebendazole.

Strongyloides stercoralis

Thread Worm.

Epidemiology of Strongyloides stercoralis

New parasite, broad range of hosts.

Diagnosis of Strongyloides stercoralis

Continuous mucous diarrhea changing to dysentery, rhabditiform larvae in fresh stool.

Treatment for Strongyloides stercoralis

Ivermectin, Albendazole.

Dracunculus medinensis

Guinea Worm/Firey Serpent.

Pathology of Dracunculus medinensis

Lesion on foot or ankles, worm grows up leg and sometimes damages knee joint.

Diagnosis of Dracunculus medinensis

Observation of anterior portion of worm, ulcer, release of larvae.

Wuchereria bancrofti

Bancroft's Filariasis or Elephantiasis.

Diagnosis of Wuchereria bancrofti

Blood smear - microfilaria in blood, serology - antibody to worm.

Loa loa

Eye worm.

Pathology of Loa loa

Worms move freely through subcutaneous tissues, can wander across eyes.

Onchocerca volvulus

River Blindness.

Diagnosis of Onchocerca volvulus

Skin biopsy to look for microfilaria.

Dirofilaria immitis

Heartworm in dogs/cats.