''Contracaecum'' is genus of parasitic

nematodes The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...

from the family

Anisakidae The Anisakidae are a family of intestinal nematodes (roundworms). The larvae of these worms can cause anisakiasis when ingested by humans, in raw or insufficiently cooked fish. Anisakidae worms can infect many species of fish, birds, mammals and ...

. These nematodes are parasites of warm-blooded, fish eating animals, i.e. mammals and birds, as sexually mature adults. The eggs and the successive stages of their larvae use invertebrates and increasing size classes of fishes as intermediate hosts. It is the only genus in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

which can infect terrestrial, marine and freshwater animals.

Life cycle

The adults live as parasites in the stomachs of

piscivorous A piscivore () is a carnivorous animal that eats primarily fish. The name ''piscivore'' is derived . Piscivore is equivalent to the Greek-derived word ichthyophage, both of which mean "fish eater". Fish were the diet of early tetrapod evoluti ...

birds and mammals. As third stage larvae they attach to the stomach of the species of fish which are preyed on by their

definitive host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...

. When the intermediate host fish is eaten and reached the warm stomach of its predator the larvae of ''Contracaecum'' moult twice into adult males and females, producing eggs which are expelled into water in the

faeces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

of the host. Where the water is shallow the eggs or larvae descend to the sea bed. Here they may be consumed by invertebrates while those that float in the water column are ingested by various

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

. The small invertebrates and zooplankton are then eaten by larger organisms moving up the food chain until a fish suitable as a transport host consumes the larvae with the previous host. In this fish host, the larvae penetrate the wall of the intestinal tract into the organs and body cavity. The immune system of the fish reacts by producing a capsule of connective tissue around the larva, this capsule retains the larvae for the fish's life. Once an infected fish or the discarded guts of a cleaned fish are eaten by another fish, the capsule around the larvae is digested, freeing the larvae to restart this stage of its life cycle. In larger and older specimens of predatory fish there may be hundreds, possibly thousands of the larvae-containing capsules of connective tissue, these are all third-stage larvae and they are characterised by having and tooth-like structure on their head which is used to bore through the host's tissues. They have no reproductive organs at this stage. ''Contracaecum'' nematodes are common in wild salmonids in the marine environment where they may occur abundantly. When they reach their final host they develop into adults. Dependent on the species of ''Contracaecum'' the definitive host can be mammals, including humans, birds, and in some cases, fish. In experiments third stage larvae of ''

Contracaecum osculatum ''Contracaecum'' is genus of parasitic nematodes from the family Anisakidae. These nematodes are parasites of warm-blooded, fish eating animals, i.e. mammals and birds, as sexually mature adults. The eggs and the successive stages of their larvae ...

'' were shown to be infective of copepods, for example the larvae measuring 300-320

micron The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

s infected nauplius larvae of '' Balanus'' and small species of fish such as

stickleback The sticklebacks are a family of ray-finned fishes, the Gasterosteidae which have a Holarctic distribution in fresh, brackish and marine waters. They were thought to be related to the pipefish and seahorses but are now thought to be more closel ...

and

eelpout The eelpouts are the ray-finned fish family Zoarcidae. As the common name suggests, they are somewhat eel-like in appearance. All of the roughly 300 species are marine and mostly bottom-dwelling, some at great depths. Eelpouts are predominantly ...

. Larger fish such as

flatfish A flatfish is a member of the Ray-finned fish, ray-finned demersal fish order (biology), order Pleuronectiformes, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the ...

and

gobies Gobiidae or gobies is a family of bony fish in the order Gobiiformes, one of the largest fish families comprising more than 2,000 species in more than 200 genera. Most of gobiid fish are relatively small, typically less than in length, and the ...

were infected with the larvae by consuming the crustaceans while yet larger, predatory fish were infected by consuming these smaller fish. While the larvae were in the crustaceans they did not grow much, if at all. In the very small fish the larvae grew slowly and if a cod ate the small fish the smaller larvae died in the cod's liver and gut wall while the larger larvae travelled to the

parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...

of the liver. Here, some of the larvae attained lengths of up to 10 mm. Even so, some specimens of ''C. osculatum'' completed their life cycle using only a copepd host and a single intermediate host such as a stickleback.

Distribution

The nematodes in the genus ''Contracaecum'' are found in seas throughout the globe. It is the most speciose genus in the Anisakidae.

Effects on human health

''Contracaecum'' larvae can infect humans, the human disease caused by infection of Anisakid nematodes such as ''Contracaecum'' is called

anisakiasis ''Anisakis'' (a·nuh·saa·keez) is a genus of parasitic nematodes that have life cycles involving fish and marine mammals. They are infective to humans and cause anisakiasis. People who produce immunoglobulin E in response to this parasite may ...

(or anisakidosis) which is a painful and severe condition with infection usually being caused by the consumption of raw or undercooked fish which are host to the third stage larvae. The

symptoms Signs and symptoms are the observed or detectable signs, and experienced symptoms of an disease, illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormali ...

of anisakiasis include abdominal pain and distention, diarrhea and nausea, faeces with high proportions of blood and mucus and a mild fever. There can also be allergic reactions such as rash and itching, and occasionally there can also be

anaphylaxis Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follow ...

. Patients may require the removal of the parasite by

endoscopy An endoscopy is a procedure used in medicine to look inside the body. The endoscopy procedure uses an endoscope to examine the interior of a hollow organ or cavity of the body. Unlike many other medical imaging techniques, endoscopes are insert ...

surgery Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...

to treat this condition.

Species

There are 142 species in the genus ''Contracaecum''.

References

{{Taxonbar, from=Q2995709 Nematodes