Measures against Echinococcus multilocuralis
Targeting the Source of Human Infection
OIE reference lab. on echinococcosis and Lab. Parasitology,
Univ., Graduate School of Vet. Med.
During the mid-twentieth century, there was an expression of“This
Wormy World(Stoll , 1947: J. Parasitol.)”to describe the abundance of
parasitic worms in our society. However, with the widespread use of
antihelmintics, roundworms and the related helminths had been almost
eradicated in Japan. Nevertheless, with the increase of garbage from
kitchens and from agricultural and fisheries waste materials as food for
wildlife such as the red fox, the epidemiology of certain parasites had
In August 1999, Echinococcus multilocularis metacestodes were found
in pigs in Aomori prefecture, on the mainland of Japan. Thus, the endemic
area for this cestode, which had been hitherto confined to Hokkaido has
been extended to the mainland of Japan. When this parasite infects the
human body, it causes clinical signs similar to that of hepatic tumor for
more than a decade. Since there is no effective antihelmintic for this
alveolar hydatid disease, therapy is difficult when the patient starts to
show clinical signs. In Hokkaido, ca. 400 people had been confirmed as
having the lesions caused by this parasite and most cases of the disease
had been reported fatal.
Echinoccocus multilocularis has skillfully adapted its life cycle
to the predator-prey(foxes-voles) relationship. Humans are infected by
ingestion of the parasite ova excreted from the predator. Human to human,
or pig to human transmission of the parasite does not occur.
In April 1999, with the enactment of the“New Infectious Disease
Ordinance”, human echinococcosis, as diagnosed by detection of the
parasite or the antibody against it, must be reported to the authorities
within 7 days. Although such regulation had been highly regarded, much
more needs to be done. The most important measure is to eradicate the
source of infection of this disease. There is a need to identify and
control the animal hosts that disperse the parasite eggs and also to set
up a systematic program for controlling and containing the spread of the
Until the 1970's it was thought that echinococcosis in Hokkaido
could be controlled by cutting one third of all foxes on the island, but
such a measure proved to be fruitless. Studies on fox behavior had shown
that they inhabit a defined territory or domain and that if a certain fox
had been killed in a certain area, other foxes from the surrounding
territory would move into the culled fox domain. Thus, the culling of
foxes is thought to be counterproductive and has resulted in the
migration of infected foxes and an increased infection rate among the
animals, leading to further spread of the disease.
Presently, the prevalence of echinococcosis in Hokkaido foxes is
about 60％ and the parasite has also been detected in pet dogs and cats.
If no actions are taken to control the source of infection of this
parasite, then its spread to Honshu on the main land of Japan, will
become a matter of time.
Several years ago, our research group at Hokkaido University
developed a diagnostic method for fox detecting antigen in the feces of
the infected fox, whereby it is not necessary to kill the animal in order
to diagnose the infection.
In 1998, a deworming program to eradicate echinococcosis in wild
foxes, involving more than 10,000 hours per year was carried out by our
research group, in a pilot area facing the Sea of Okhotsk in
northern-eastern Hokkaido, covering 200 Km2. The wild foxes were fed meat
and fish sausage containing the antihelmintic, Praziquantel. Using the
coproantigen detecting method and fecal examination, it was observed that
the number of foxes excreting the Echinococcus eggs had been reduced to
almost zero despite the fact that some foxes were still positive for the
coproantigen test which indicates there are still infected intermediate
voles in the area. Thus, it is thought that if the deworming program were
carried out more extensively, there is a possibility of eradicating the
source of infection of the parasite from all foxes.
In an echinococcosis control pilot program that was carried out in
southern Germany about 10 years ago, wild foxes were fed antihelmintic
and then killed to evaluate the effectiveness of the deworming program.
In the peripheral pilot area, the effectiveness of the deworming program
was quite low due to the movement of other infected foxes into the test
area following the culling of foxes there. However, the prevalence of
echinococcosis among foxes in the center of the pilot area had been
completely eradicated. Thus, both Japanese and German researchers had
shown that it is possible to clean up our environment contaminated by
In 1994, the Parasitology Department of the Faculty of Veterinary
Medicine, Hokkaido University, was designated as a reference center for
echinococcosis by OIE. Since then, the aforementioned department has
been collaborating with researchers from other endemic areas such as
Uruguay, France and China, as well as with officials from international
organizations such as FAO and WHO, in attempts to control the source of
infection of the echinococcosis. Collaborative networks were also forged
with researchers in EU countries in the form of exchange of scientific
information as well as diagnostic reagents and antihelmintics used in
sylvatic control programs.
A measure to control echinococcosis had not been taken by the
Japanese government authority. In this context, I would like to propose 3
points, which will not only help solve the echinococcosis problem
domestically but also contribute to international cooperation.
The first is to add to the “New Infectious Disease Ordinance” the
duty to authorities the authority the prevalence of Echinococcus infected
径animals which serve as the source of infection to humans, as well as
the establishment of the diagnosis and quarantine of these animals.
The second is to establish a specialize research organization with
facilities and human resources to handle infected animals and the ability
to response to the needs of each individual local situation. For example,
using the local agricultural and fisheries waste products to develop
antihelmintic-laced baits for the deworming program of the infected
foxes, development of a parasite vaccine for the foxes and training of
experts and technicians to educate the public on prevention of the
The third is to establish a network among international researchers
where information exchange and scientific collaboration can transcend the
borders of their countries in order to establish and perfecting the
disease control program. This includes the free flow of information on
the sources of infection, on techniques regarding the prevention of
infection, and on the extension of technical cooperation to the endemic
areas. These proposals are in line with the policy on the International
Control of Parasitic Diseases (the so-called "Hashimoto Initiative")as
proposed by Japan in the 1998 summit meeting in Birmingham, England.
LOOK JAPAN 「OUTFOXING ECHINOCOCCUS」AUGUST 1999, 29
「DETENER AL EQUINOCOCO」AGOSTO 1999, 13
北海道大学広報誌 季刊 リテラ・ポプリ、「旅をする寄生虫：WANDERING
KAMIYA Masao, D.V.M., Ph.D.
Hokkaido Univ., Graduate School of Vet. Med.
Kita-18, Nishi-9, Sapporo 060-0818, Japan