Anisakis simplex and related worms

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Anisakis simplex and related worms

 

1. Name of the Organism:

Anisakis simplex and related worms

 

Anisakis simplex (herring worm), Pseudoterranova (Phocanema, Terranova)

decipiens (cod or seal worm), Contracaecum spp., and Hysterothylacium

(Thynnascaris) spp. are anisakid nematodes (roundworms) that have been

implicated in human infections caused by the consumption of raw or undercooked

seafood. To date, only A. simplex and P. decipiens are reported from human cases

in North America.

 

2. Nature of Acute Disease:

 

Anisakiasis is generally used when referring to the acute disease in humans.

Some purists utilize generic names (e.g., contracaeciasis) in referring to the

disease, but the majority consider that the name derived from the family is

specific enough. The range of clinical features is not dependent on species of

anisakid parasite in cases reported to date.

 

3. Nature of Disease:

 

In North America, anisakiasis is most frequently diagnosed when the affected

individual feels a tingling or tickling sensation in the throat and coughs up or

manually extracts a nematode. In more severe cases there is acute abdominal

pain, much like acute appendicitis accompanied by a nauseous feeling. Symptoms

occur from as little as an hour to about 2 weeks after consumption of raw or

undercooked seafood. One nematode is the usual number recovered from a patient.

With their anterior ends, these larval nematodes from fish or shellfish usually

burrow into the wall of the digestive tract to the level of the muscularis

mucosae (occasionally they penetrate the intestinal wall completely and are

found in the body cavity). They produce a substance that attracts eosinophils

and other host white blood cells to the area. The infiltrating host cells form a

granuloma in the tissues surrounding the penetrated worm. In the digestive tract

lumen, the worm can detach and reattach to

other sites on the wall. Anisakids rarely reach full maturity in humans and

usually are eliminated spontaneously from the digestive tract lumen within 3

weeks of infection. Penetrated worms that die in the tissues are eventually

removed by the host's phagocytic cells.

 

4. Diagnosis of Human Illness:

 

In cases where the patient vomits or coughs up the worm, the disease may be

diagnosed by morphological examination of the nematode. (Ascaris lumbricoides,

the large roundworm of humans, is a terrestrial relative of anisakines and

sometimes these larvae also crawl up into the throat and nasal passages.) Other

cases may require a fiber optic device that allows the attending physician to

examine the inside of the stomach and the first part of the small intestine.

These devices are equipped with a mechanical forceps that can be used to remove

the worm. Other cases are diagnosed upon finding a granulomatous lesion with a

worm on laparotomy. A specific radioallergosorbent test has been developed for

anasakiasis, but is not yet commercially marketed.

 

5. Associated Foods:

 

Seafoods are the principal sources of human infections with these larval

worms. The adults of A. simplex are found in the stomachs of whales and

dolphins. Fertilized eggs from the female parasite pass out of the host with the

host's feces. In seawater, the eggs embryonate, developing into larvae that

hatch in sea water. These larvae are infective to copepods (minute crustaceans

related to shrimp) and other small invertebrates. The larvae grow in the

invertebrate and become infective for the next host, a fish or larger

invertebrate host such as a squid. The larvae may penetrate through the

digestive tract into the muscle of the second host. Some evidence exists that

the nematode larvae move from the viscera to the flesh if the fish hosts are not

gutted promptly after catching. The life cycles of all the other anisakid genera

implicated in human infections are similar. These parasites are known to occur

frequently in the flesh of cod, haddock, fluke, pacific salmon,

herring, flounder, and monkfish.

 

6. Relative Frequency of Disease:

 

Fewer than 10 cases are diagnosed in the U.S. annually. However, it is

suspected that many other cases go undetected. The disease is transmitted by

raw, undercooked or insufficiently frozen fish and shellfish, and its incidence

is expected to increase with the increasing popularity of sushi and sashimi

bars.

 

7. Course of Disease and Complications:

 

Severe cases of anisakiasis are extremely painful and require surgical

intervention. Physical removal of the nematode(s) from the lesion is the only

known method of reducing the pain and eliminating the cause (other than waiting

for the worms to die). The symptoms apparently persist after the worm dies since

some lesions are found upon surgical removal that contain only nematode

remnants. Stenosis (a narrowing and stiffening) of the pyloric sphincter was

reported in a case in which exploratory laparotomy had revealed a worm that was

not removed.

 

8. Target Populations:

 

The target population consists of consumers of raw or underprocessed seafood.

 

9. Food Analysis:

 

Candling or examining fish on a light table is used by commercial processors

to reduce the number of nematodes in certain white-flesh fish that are known to

be infected frequently. This method is not totally effective, nor is it very

adequate to remove even the majority of nematodes from fish with pigmented

flesh.

 

10. Selected Outbreaks:

 

Literature references can be found at the links below.

This disease is known primarily from individual cases. Japan has the greatest

number of reported cases because of the large volume of raw fish consumed there.

A recent letter to the editor of the New England Journal of Medicine

(319:1128-29, 1988) stated that approximately 50 cases of anisakiasis have been

documented in the United States, to date. Three cases in the San Francisco Bay

area involved ingestion of sushi or undercooked fish. The letter also points out

that anasakiasis is easily misdiagnosed as acute appendicitis, Crohn's disease,

gastric ulcer, or gastrointestinal cancer.

 

more on site

 

http://vm.cfsan.fda.gov/~mow/chap25.html

 

 

 

 

" Respect means listening until everyone has been heard and understood, only

then is there a possibility of " Balance and Harmony " the goal of Indian

Spirituality. " Dave Chief, Grandfather of Red Dog

 

 

 

 

 

 

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