Zoonoses transmitted by companion animals: hydatidosis

Zoonoses transmitted by companion animals: hydatidosis

1. Definition and geographic distribution

Hydatidosis and echinococcosis are terms that are applied interchangeably to refer to the parasitic processes caused by the adult and larval forms of tapeworms belonging to the genus Echinococcus. In Spain, the disease does not present a homogeneous distribution, being more frequent in Aragon, Extremadura, Castilla la Mancha and Castilla y León (which occupies one of the first places in terms of incidence rates) soundcloud.

2. Biological cycle. Description


The adult tapeworm has a typical flattened shape and, like other tapeworms, its body can be divided into three regions:

  • Scolex or organ of attachment
  • Neck
  • strobile It constitutes the largest part of the body, and is formed by a chain of rings (proglottids) in varying degrees of sexual maturation and pregnancy. The gravid proglottids detach from the body of the cestode from time to time, thus allowing the exit of the eggs to the outside, with the fecal waste.

Echinococcus granulosus is a small tapeworm, 2 to 8 mm in length, and whose strobila is made up of three or even four proglottids. The larval form of E. granulosus is a hydatid cyst, which can develop into a variety of viscera.

Biological cycle:

Tapeworms of the genus Echinococcus sp. they have an indirect biological cycle, with the intervention of a definitive host (domestic dog and various wild canids), and an intermediate host, represented by a multitude of herbivorous mammals (with special mention of sheep).

Man constitutes an accidental intermediate host, whose epidemiological interest resides, not in the role he plays as such a host, by constituting a cul-de-sac for the cycle, but in the role he plays by perpetuating the presence of the parasite in the environment with concrete actions such as feed raw cyst-bearing offal directly to your dogs, or leave these potentially infested dead animals within reach.

3. Epidemiology

The diffusion and maintenance of hydatidosis requires, fundamentally, the existence of certain determining factors of a sociological type related to livestock or hunting practices that allow the perpetuation of the biological cycle of the parasite.

The epidemiology of E. granulosus is determined by the concurrence of a series of factors that are:

  1. Initial Necessary Factors
    • Coexistence in the same environment as the definitive and intermediate hosts (mainly dog/sheep).
    • Relationship between the two that supposes the consumption of viscera of the second by the first.
    • Presence of the parasite.
  2. extrinsic factors
    • Adequate environmental temperature and humidity for the survival of eggs in the environment.
    • Existence of dispersing agents that distribute the eggs from the feces to the environment.
  3. Socioeconomic factors
    • Inadequate agricultural, livestock and hunting practices (supply of viscera to dogs as food, abandonment of carcasses, use of irrigation water of poor microbiological quality, etc.)
    • Habits: contact with dogs, consumption of contaminated water or unwashed fresh products (fruits and vegetables), contamination of hands through contact with contaminated soil.
    • Level of training and information of citizens, especially in the regions where the problem is more frequent.

In our environment, the dog-sheep cycle is the most important. Sheep are the most relevant intermediate host for several reasons: the infestation rate is usually high in these animals (especially high in animals older than 5 years from regions with high prevalence), their cysts are 90% or more fertile In all cases, it has a close association with dogs, and it is the animal that is preferably sacrificed for immediate internal family consumption.

4. Pathogenesis

The damage caused by adult tapeworms in dogs is limited to local lesions in the intestinal mucosa.

In the intermediate host, the pathogenic effects produced are variable depending on the host itself, the parasitized organ, the degree of infection, and the virulence of the parasite.

In men, 81-87% of the cysts are located in the liver or lung, the rest being distributed to other organs.

The main problems caused by cysts are of mechanical origin, due to their growth. However, its rupture can cause serious consequences, such as secondary bacterial infections, dissemination of the protoscolices leading to multiple secondary hydatidosis, anaphylactic reactions, or even death of the host.

5. Therapeutics

treatment in dogs

The drug of choice for the treatment of echinocosis in dogs is Praziquantel (5 mg/kg bw in a single dose) administered every 40-45 days, although experiences have also been carried out with albendazole, mebendazole or niclosamide, among others.

Point out that praziquantel is an effective parasite killer, but does not have ovicidal activity, a circumstance that must be taken into account, in relation to the management of the feces produced, if the animals are dewormed for the first time, or after using administration guidelines with deadlines longer than indicated.

Human treatment

In humans, the treatment of the disease is eminently surgical, having verified the usefulness of albendazole and mebendazole in the treatment of hepatic and pulmonary cysts, although recurrences have been described, which is why clinical follow-up of the patient is necessary for several years.

6. Prevention and control

Hydatidosis prevention and control actions must be based on three fundamental pillars:

  1. Prevent access of domestic dogs to raw viscera likely to be contaminated with larval forms of Echinococcus sp. (control in slaughterhouses, safe destruction of infected viscera, proper disposal of viscera from hunting or hunting, control of the abandonment of carcasses, etc.)
  2. Control of definitive hosts:
    • stray animal control
    • Regular treatment of dogs at risk (rural areas or areas with a high prevalence of the parasite, working dogs: herding, hunting…) and destruction of feces suspected of being contaminated.
    • health education


In summary, the fight against this zoonosis can give satisfactory results when, from health education as a fundamental basis, action programs based on knowledge of the disease are established, with special emphasis on the protection of the definitive host (domestic dog), both avoiding its parasitization by preventing its access to contaminated viscera, and preventing its activity as a disseminator of infesting eggs, through adequate deworming guidelines.