Capillaria hepatica
Encyclopedia
Capillaria hepatica is a parasitic nematode which causes Hepatic capillariasis in rodents and numerous other mammal species, including humans. The life cycle of C. hepatica may be completed in a single host species. However, the eggs, which are laid in the liver, must mature outside of the host body (in the environment) prior to infecting a new host . So the death of the host in which the adults reach sexual maturity, either by being eaten or dying and decomposing, is necessary for completion of the life cycle.
, requiring only one host to complete its life cycle . Adults are often found in dozens of rodent species, but also occur in a wide variety of other wild and domestic mammals, and occasionally humans. C. hepatica has been found in temperate and tropical zones on every continent, with the exception of Australia, and infestation rates of wild-caught rats of up to 100% have been reported.
Usually, Capillaria hepatica is found in rodents, monkeys and other animals. Capillaria hepatica is rarely found in humans and at least 40 cases have been reported. There are no endemic areas of infection with C. hepatica and human infection primarily results from Zoonotic
transmission .
Of the human infections, most have been found in children.
of this parasite is the liver. The adult females will deposit eggs in the Parenchyma
of the liver. Occasionally in humans larvae will migrate to the lungs, kidneys and other organs .
Adult worms take the shape of a slender nematode, with the anterior part of the body narrow and the posterior part gradually swelling . The females measure about 53-78mm x 0.11-0.20mm, but the males are approximately 24-37mm x 0.07-0.10mm . The adult worms are rarely seen intact, as they mature and die in the Parenchyma
of the liver . The adult females lay eggs that are about 48-66μm x 28-36μm . The shell of the eggs is striated with shallow polar prominences at either end. Numerous mini-pores can be seen in the outer shell as well. Unembryonated eggs may be ingested by a carnivore, in which case they are harmless and pass out in the feces. Eggs will embryonate in the environment, where they require air and damp soil to become infective. Under optimal conditions this takes about 30 days. Larvae are juvenile versions of the adult worm .
. Development from the L1 stage to sexually mature adults occurs in the liver within 18–21 days . Eggs are laid in the liver parenchyma
of the host throughout the adult worm's life span, which lasts for about 30–40 days . Up to 938,000 eggs have been reported from the liver of a single rodent host.
The eggs in the liver exist in a state of arrested development they are unable to develop into larvae until they spend some time outside of the host, in the environment. Escaping from the liver tissue may be accomplished either by the death and decomposition of the host's body, or by the consumption and digestion of the host by a predator or scavenger
. If the host is eaten, the eggs will pass into the environment in the feces of the predator or scavenger. In the environment, eggs require 4–5 weeks to develop, and may remain viable in a dormant state for several more months. Once these "environmentally-conditioned" eggs are eaten by a suitable host, the first stage larvae (L1) hatch in the intestine and continue the life cycle. Humans are usually infected after ingesting embryonated eggs in fecal-contaminated food, water, or soil .
wanders through the host liver causing loss of liver cells and thereby loss of function . However, as the adult C. hepatica begin to die in the liver tissue, their decomposition accelerates the immune response of the host. This response leads to chronic inflammation
and Encapsulation
of the dead worms in collagen
fibers, and eventually to septal fibrosis
(abnormal connective tissue growth) and cirrhosis
of the liver. This leaves the eggs behind and they can become encased by Granulomatous tissue, with large sections of the Parenchyma
becoming replaced by these egg masses . Capillaria hepatica can also cause Hepatomegaly
. Infections of C. hepatica can present with several clinical symptoms including, abdominal pain in the liver area, weight loss, decreased appetite, fever and chills, hepatitis
(liver inflammation), ascites
(excess fluid in the peritoneal cavity) and hepatolithiasis
(gallstones in the bile ducts). .
This parasite can be fatal in humans, as transmission and survival of the parasite depend on death of the Definitive host in order for the eggs to reach soil and water to embryonate.
. Key identification features of this parasite are a striated shell and shallow polar prominences of the egg and a narrowing at anterior end and gradual swelling at posterior end of the adult worm. Identification of C. hepatica eggs in the stool does not result from infection of the human host, but from ingestion by that host of livers from infected animals, the eggs will then pass out harmlessly in the feces . Most cases have been determined after death because clinical symptoms resemble those of numerous liver disorders .
The drug of choice for treating Capillaria hepatica is Mebendazole, with Albendazole as an alternative . Successful treatment of human cases with thiabendazole
or albendazole
(with or without corticosteroid
s) have been reported. Albendazole must be taken with food because a fatty meal will increase the Bioavailability
of the drug .
Two ways of preventing C. hepatica infections is humans would be to institute effective rodent control programs and preventing dogs and cats from eating rodents .
drugs.
In Australia, several releases of Capillaria hepatica eggs in the field have been unable to control rapidly expanding populations of mice.
Discovery and taxonomy
This species was first described in 1893, from specimens found in the liver of Rattus norvegicus, and named Trichocephalus hepaticus. Various authors have subsequently renamed it Trichosoma hepaticum, Capillaria hepatica, Hepaticola hepatica and Calodium hepaticum. Currently it is usually referred to as either Capillaria hepatica or, less often, Calodium hepaticum.Hosts and distribution
This parasite is MonoxenousMonoxenous Development
Monoxenous DevelopmentIn many parasitic groups the whole development is restricted to the tissues of one host individual.The species may be strictly host specific or not ....
, requiring only one host to complete its life cycle . Adults are often found in dozens of rodent species, but also occur in a wide variety of other wild and domestic mammals, and occasionally humans. C. hepatica has been found in temperate and tropical zones on every continent, with the exception of Australia, and infestation rates of wild-caught rats of up to 100% have been reported.
Usually, Capillaria hepatica is found in rodents, monkeys and other animals. Capillaria hepatica is rarely found in humans and at least 40 cases have been reported. There are no endemic areas of infection with C. hepatica and human infection primarily results from Zoonotic
Zoonosis
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were zoonotic...
transmission .
Of the human infections, most have been found in children.
Tissue Niche and Morphology
The tissue NicheNiche
Niche may refer to:*Niche , an exedra or an apse that has been reduced in size;*Niche , Colombian/Spanish football player, full name Víctor Manuel Micolta Armero*Niche , a British Thoroughbred racehorse...
of this parasite is the liver. The adult females will deposit eggs in the Parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
of the liver. Occasionally in humans larvae will migrate to the lungs, kidneys and other organs .
Adult worms take the shape of a slender nematode, with the anterior part of the body narrow and the posterior part gradually swelling . The females measure about 53-78mm x 0.11-0.20mm, but the males are approximately 24-37mm x 0.07-0.10mm . The adult worms are rarely seen intact, as they mature and die in the Parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
of the liver . The adult females lay eggs that are about 48-66μm x 28-36μm . The shell of the eggs is striated with shallow polar prominences at either end. Numerous mini-pores can be seen in the outer shell as well. Unembryonated eggs may be ingested by a carnivore, in which case they are harmless and pass out in the feces. Eggs will embryonate in the environment, where they require air and damp soil to become infective. Under optimal conditions this takes about 30 days. Larvae are juvenile versions of the adult worm .
Life cycle
Hosts ingest C. hepatica eggs (from sources outlined below) which hatch into first stage larvae (L1). The L1 larvae bore through the intestinal wall and are carried to the liver by the hepatic portal veinHepatic portal vein
The hepatic portal vein is not a true vein, because it does not conduct blood directly to the heart. It is a vessel in the abdominal cavity that drains blood from the gastrointestinal tract and spleen to capillary beds in the liver...
. Development from the L1 stage to sexually mature adults occurs in the liver within 18–21 days . Eggs are laid in the liver parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
of the host throughout the adult worm's life span, which lasts for about 30–40 days . Up to 938,000 eggs have been reported from the liver of a single rodent host.
The eggs in the liver exist in a state of arrested development they are unable to develop into larvae until they spend some time outside of the host, in the environment. Escaping from the liver tissue may be accomplished either by the death and decomposition of the host's body, or by the consumption and digestion of the host by a predator or scavenger
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
. If the host is eaten, the eggs will pass into the environment in the feces of the predator or scavenger. In the environment, eggs require 4–5 weeks to develop, and may remain viable in a dormant state for several more months. Once these "environmentally-conditioned" eggs are eaten by a suitable host, the first stage larvae (L1) hatch in the intestine and continue the life cycle. Humans are usually infected after ingesting embryonated eggs in fecal-contaminated food, water, or soil .
Pathogenesis and Survival in Host
In humans C. hepatica causes Hepatic capillariasis, a serious liver disorder . The NematodeNematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
wanders through the host liver causing loss of liver cells and thereby loss of function . However, as the adult C. hepatica begin to die in the liver tissue, their decomposition accelerates the immune response of the host. This response leads to chronic inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
and Encapsulation
Encapsulation
- Chemistry :* Molecular encapsulation, in chemistry, the confinement of an individual molecule within a larger molecule* Capsule , in pharmacy, the enclosure of a medicine within a relatively stable shell for administration...
of the dead worms in collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
fibers, and eventually to septal fibrosis
Fibrosis
Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process. This is as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue...
(abnormal connective tissue growth) and cirrhosis
Cirrhosis
Cirrhosis is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrosis, scar tissue and regenerative nodules , leading to loss of liver function...
of the liver. This leaves the eggs behind and they can become encased by Granulomatous tissue, with large sections of the Parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
becoming replaced by these egg masses . Capillaria hepatica can also cause Hepatomegaly
Hepatomegaly
Hepatomegaly is the condition of having an enlarged liver. It is a nonspecific medical sign having many causes, which can broadly be broken down into infection, direct toxicity, hepatic tumours, or metabolic disorder. Often, hepatomegaly will present as an abdominal mass...
. Infections of C. hepatica can present with several clinical symptoms including, abdominal pain in the liver area, weight loss, decreased appetite, fever and chills, hepatitis
Hepatitis
Hepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cells in the tissue of the organ. The name is from the Greek hepar , the root being hepat- , meaning liver, and suffix -itis, meaning "inflammation"...
(liver inflammation), ascites
Ascites
Ascites is a gastroenterological term for an accumulation of fluid in the peritoneal cavity.The medical condition is also known as peritoneal cavity fluid, peritoneal fluid excess, hydroperitoneum or more archaically as abdominal dropsy. Although most commonly due to cirrhosis and severe liver...
(excess fluid in the peritoneal cavity) and hepatolithiasis
Hepatolithiasis
Hepatolithiasis is the presence of gallstones in the biliary ducts of the liver. Treatment is usually surgical. It is rare in Western countries, but prevalent in East Asia....
(gallstones in the bile ducts). .
This parasite can be fatal in humans, as transmission and survival of the parasite depend on death of the Definitive host in order for the eggs to reach soil and water to embryonate.
Diagnosis and treatment
Diagnosis is made by finding eggs or adults of C. hepatica in liver tissue from biopsy or Necropsy samples . The encapsulated eggs and adults may appear as white nodules which measure 2–3mm in diameter on the surface and interior of the liver at autopsyAutopsy
An autopsy—also known as a post-mortem examination, necropsy , autopsia cadaverum, or obduction—is a highly specialized surgical procedure that consists of a thorough examination of a corpse to determine the cause and manner of death and to evaluate any disease or injury that may be present...
. Key identification features of this parasite are a striated shell and shallow polar prominences of the egg and a narrowing at anterior end and gradual swelling at posterior end of the adult worm. Identification of C. hepatica eggs in the stool does not result from infection of the human host, but from ingestion by that host of livers from infected animals, the eggs will then pass out harmlessly in the feces . Most cases have been determined after death because clinical symptoms resemble those of numerous liver disorders .
The drug of choice for treating Capillaria hepatica is Mebendazole, with Albendazole as an alternative . Successful treatment of human cases with thiabendazole
Thiabendazole
Tiabendazole is a fungicide and parasiticide.-Fungicide:...
or albendazole
Albendazole
Albendazole, marketed as Albenza, Eskazole, Zentel and Andazol, is a member of the benzimidazole compounds used as a drug indicated for the treatment of a variety of worm infestations. Although this use is widespread in the United States, the U.S. Food and Drug Administration has not approved...
(with or without corticosteroid
Corticosteroid
Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte...
s) have been reported. Albendazole must be taken with food because a fatty meal will increase the Bioavailability
Bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered...
of the drug .
Two ways of preventing C. hepatica infections is humans would be to institute effective rodent control programs and preventing dogs and cats from eating rodents .
Research uses
The selective liver damage by C. hepatica in rodents has been used in model systems to study the extensive regeneration capabilities of the mammalian liver, and for testing antifibroticFibrosis
Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process. This is as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue...
drugs.
In Australia, several releases of Capillaria hepatica eggs in the field have been unable to control rapidly expanding populations of mice.
Further reading
- http://indianpediatrics.net/oct2007/781.pdf
- http://www.springerlink.com/content/q0g88772134046j5/ Journal Indian Journal of Pediatrics Publisher Dr. K C Chaudhuri Foundation, co-published by Springer India
- Camargo L. M. A. et al. (2010). "Capillariaisis (Trichurida, Trichinellidae, Capillaria hepatica) in the Brazilian Amazon: low pathogenicity, low infectivity and a novel mode of transmission". Parasites & VectorsParasites & VectorsParasites & Vectors is a peer-reviewed open-access medical journal published by BioMed Central. The journal publishes articles on the biology of parasites, parasitic diseases, intermediate hosts, vectors and vector-borne pathogens. Parasites & Vectors was established in 2008 as a merger of Filaria...
3: 11. doi:10.1186/1756-3305-3-11.