Capillaria hepatica

Geographic Range

Capillaria hepatica has been recorded in Africa, Asia, Australia, Europe, and North, Central and South America. The eggs of C. hepatica can withstand various weather conditions and may remain unembryonated in the soil for long periods of time (> 1 year), which has contributed to the success of this species in several different climates.

• Biogeographic Regions
• nearctic nearctic
• palearctic palearctic
• oriental oriental
• ethiopian ethiopian
• neotropical neotropical
• australian australian

Habitat

Capillaria hepatica is common in areas with poor hygiene and high rodent populations. On a smaller scale, within the body of its host, the larvae of C. hepatica hatch in the small intestine and spend most of their juvenile life migrating towards the liver, which is the final destination of the adults. The unembryonated eggs are excreted from the feces of the host and are then deposited in the soil. Ideal conditions for survival and embryonation of the ova are a cool and moist environment.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest

• Other Habitat Features
• urban urban
• agricultural agricultural
• caves

Physical Description

This species can be identified as one of the two genera in the superfamily Trichuroidea that has bacillary bands, which consist of specialized cuticle and an underlying hypodermis extending the length of the body. Capillaria hepatica has cuticles shed at various points in the life cycle, characteristic of the nematodes. Adult males are 24-37 mm long and .04 to .08 mm in diameter. Adult females are larger than males and are approximately 53-78 mm in length and 0.19 mm in diameter. Capillaria hepatica has a muscular esophagus that is half of the females body and a third of the males body. The female's vulva is located posterior to the esophagus. The eggs are oval and in a double layer shell that has many minipores on it. The nonembryonated eggs are approximately 55.8 by 30 μm.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

Capillaria hepatica is a special nematode because it is the only known helminth with a direct life cycle that requires the host to die for proper transmission. Eggs are deposited and embedded in the liver from the female worm and do not further develop until they are released from the organ. The eggs survive outside the host in an environment rich in oxygen, but nonetheless they are very resistant to the environment. They are liberated by cannibalism, predation, or necrophagy (feeding on carion) of an infected liver. After the new host consumes the egg, within 24 hours the egg hatches and the first stage larvae burrow into the cecal wall. The larvae move to the hepatic vein and the first molt in the larvae occurs approximately three days after the infection. Second stage larvae retain the shed cuticle as a sheath and a second molt takes place. Reproductive organs begin to form in the third larvae stage and the third molt takes place. The fourth stage larvae have a distinguished spicule and the cuticle is lost. This stage is also when sexual dimorphism is visible. Lastly, they will experience their final ecdysis, become fifth stage larvae and then adults. The female releases eggs in clumps around her body and then dies. The eggs become encapsulated in host tissue and protected until they begin development once released from the liver, upon death and decomposition of the host, or when the liver is eaten by a predator. If the liver disintegrates, the eggs are released into the soil and can be picked up by a new host. However, if cannibalism occurs, the eggs may pass through the predator undeveloped and be released in the feces. Then, they can embryonate and become infective for a new host because only embryonated eggs cause infection.

Reproduction

Males have a long funnel-like spicule sheath that serves as a chemosensory organ. This likely serves in reproduction as the spicule helps hold the female during insemination.

The spicule helps hold the female’s vagina during insemination. The females have a vulva located near the esophagus. Approximately twenty-eight days after mating, the production of eggs occurs.

• Key Reproductive Features
• sexual sexual
• oviparous oviparous

Females of Capillaria hepatica lay eggs in clusters surrounding the adults and the eggs become encapsulated and protected by host tissue.

• Parental Investment
• female parental care female parental care
• inherits maternal/paternal territory

Lifespan/Longevity

Laboratory trials found the life­span of the female is about 59 days and about 40 days for males.

Behavior

Capillaria hepatica is a non specific parasitic nematode that mostly affects rodents and rarely infects humans (there are less than 40 documented cases). The transmission of the eggs is unique because they remain in the liver until the host is eaten by a new host or until the host decomposes after death and embryonation takes place in the soil. Carnivorous animals living in a cliff habitat are the most frequently infected. The larvae of C. hepatica hatch in the small intestine and are then transported to the liver of the host where it lives as an adult. Eggs laid by the adult females become enclosed in host tissue and develop once released from the liver.

• Key Behaviors
• parasite parasite
• motile motile

Communication and Perception

Capillaria hepatica has cephalic sense organs that help in sensory perception. Their sensilla can function as chemoreceptors, in addition to mechanoreceptors. The centrioles in the sensory dendrites of C. hepatica consist of nine doublets. Additionally, the male’s sheath serves as a chemosensory organ to detect the female.

• Communication Channels
• tactile tactile
• chemical chemical

• Perception Channels
• tactile tactile
• chemical chemical

Food Habits

Capillaria hepatica is surrounded by host liver cells and feeds from the enlarged cytoplasm of theses surrounding cells. This parasite is actually feeding from the reaction of the host rather than from blood or tissue fluid. Capillaria hepatica has thousands of bacillary pores that increase the surface area, as well as the capacity to absorb host nutrients. The bacillary pores are an advantage to living in the internal environment, such as the liver.

• Primary Diet
• carnivore carnivore
  • eats body fluids

• Animal Foods
• body fluids

Predation

Capillaria hepatica is not preyed on directly. The eggs are durable in various environments; however, many eggs never reach a new host because release from the decaying liver or cannibalism is necessary for transmission.

Ecosystem Roles

Capillaria hepatica primarily lives in rodents and rarely infects humans. Once the eggs are ingested and arrive at the liver of the host, they cause serious damage to hepatic tissue. If released into the soil, the eggs may survive for extended amounts of time until embryonated (>1 year).

• Ecosystem Impact
• parasite parasite

Economic Importance for Humans: Positive

Capillaria hepatica is an important biological control used especially in Australia to control the excessive rodent populations and the plagues that accompany them. Because transmission of Capillaria hepatica requires the death of the host, C. hepatica needs to be introduced early in the life cycle to see the desired result. If successful, there is a decrease in plague intensity and a very useful economic impact. C. hepatica is helping reduce the density of rodent pests in rural areas and improving agricultural crop survival.

• Positive Impacts
• controls pest population

Economic Importance for Humans: Negative

Although there are economical benefits when the rodent population is infected, C. hepatica can be dangerous for humans. Capillaria hepatica causes a zoonotic disease called hepatic capillariasis, and rodents are the reservoir. Experiments have shown humoral immunity produced by mice after ingestion of C. hepatica eggs provide no protection against infection. Capillaria hepatica not only causes liver cell death, but additionally, it causes reduced fertility of the host.

• Negative Impacts
• injures humans
  • causes disease in humans causes disease in humans
  • carries human disease

Conservation Status

There is no effort to conserve or destroy this species. Although they can be used to control rodent populations, they still pose a pathogenic threat to humans.

Other Comments

Capillaria species are parasites in many vertebrate animals but only three species infect humans; Capillaria hepatica , Capillaria aerophila and Capillaria philippinensis . Also, the lesions on the liver can sometimes be mistaken for Schistosoma mansoni .

Additional Links

Encyclopedia of Life

Contributors

Hallie Leavitt (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.

References

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