Which carnivore is the most resilient

Development cycle:

Infection occurs through the oral ingestion of eggs with infectious larvae. The larva hatches in the small intestine only a few hours after ingestion and pierces the intestinal wall in order to migrate to the lungs via the liver. From there it is coughed up and swallowed so that it ends up in the small intestine again. Here the larva develops into an adult worm and begins egg production. The eggs are now excreted. After about 14 days, the infectious larva 3 develops in the outside world in the egg, which in turn can be ingested by a new host. The roundworm eggs are very resilient. In the outside world, they survive winter or dry periods without problems and remain infectious for years.

The prepatency period, i.e. the time from infection to the first possible detection of the eggs in the feces, is 10 to 16 weeks, depending on the age and immune status of the host.

Occurrence and infection:

Horse:Parascaris equorum, (up to 30 cm long, round and white)

Parascaris equorum occurs mainly in young horses up to 5 years of age. Since immunity develops from 6 months onwards with increasing age, older horses are only affected in exceptional cases. Infection is possible in the stable as well as in the paddock or on the pasture.

dog:Toxocara canis (10-18 cm long)

The dog becomes infected with Toxocara canis by ingesting the eggs from the environment. Since the eggs remain infectious for years, the ingestion of the parasite by the dog is difficult to control and an infection is easily possible. Paratenic hosts such as small rodents can also ingest the larva and the dog ingests the parasites when it eats an infected rodent. Toxocara canis is particularly important due to puppy infections. The most important route of infection here is prenatal, i.e. before birth. If the adult mother becomes infected in the course of life, the larvae encapsulate themselves in organs or muscles with good immunity in order to go into a resting state. From the 40th day of gestation, the larvae are reactivated and transferred to the puppy. The puppy can also be infected through milk immediately after birth.

Cat:Toxocara cati

Cats usually become infected through paratenic intermediate hosts such as mice, through raw, infected meat, or through direct egg ingestion from the environment. As in dogs, in adult cats the larvae in the tissue can go into a dormant state. When pregnant, however, there is no transmission to the puppies. The puppies only become infected via the mother cat's milk. In young cats in particular, the larvae migrate through the body, after which there is ultimately massive egg excretion.

Human: Toxocara canis and Toxocara cati:

Zoonosis: Humans can also become infected by ingesting the infectious eggs, for example through contaminated vegetables or infected meat that has not been sufficiently heated. Especially for children who play in the sandpit lying in the feces of infected dogs or cats Toxocara a danger there. Since humans are a false host, the larva cannot become a sexually mature, intestinal worm. Usually there are no symptoms to be noticed. However, in some cases the larva can migrate through the liver, lungs, CNS and eyes and cause severe damage such as blindness there.


horse: The infested young animals can cough and fever. The damage to the small intestine can lead to emaciation and diarrhea. If there is a high number of parasites, especially in foals, there is a risk that worm balls lead to intestinal obstruction and ultimately to intestinal rupture.

dog and cat: In the adult animal, roundworm infections are usually symptom-free. If the immune system is good, the larvae in organs or muscles can go into a resting state and are later activated again. Young animals, poor immune status or significant infestation can lead to emaciation, distended belly, vomiting, dull coat and coughing. In addition, a massive worm infestation can lead to an intestinal obstruction or even an intestinal rupture, which can result in death.


horse: The eggs can be detected with the McMaster method as well as with the combined sedimentation flotation. Since foals are usually infected in the first few days of life, they can shed roundworm eggs from the age of 10 to 16 weeks, which can then be detected in a faecal sample.

dog and cat: The eggs can be easily detected using the flotation method.


Deworming is advisable as soon as a positive faecal sample is available. Because of the widespread resistance, it is important to monitor the effectiveness after treatment.

horse: In a herd with proven roundworm infestation, foals should be between the ages of 60 and 70. Day of life to be dewormed to prevent egg excretion and diseases. In problem populations with many foals, it can make sense in the first year of life to dewormer every 9 to 10 weeks. However, effectiveness controls should always be carried out afterwards. In the case of individual foals, e.g. in riding stables with mostly adult horses, faecal samples can be examined every 6 to 8 weeks in foals from an age of approx. 3 months and only treated in a targeted manner if parasites are detected. Hygiene measures in the stable and in the pasture further reduce the risk of infection. Therefore, horse droppings should be regularly removed from pastures, paddocks and boxes.

Dog and cat: Regular sampling and, if necessary, treatment is particularly useful because of the risk of zoonoses. Dog puppies should be dewormed for the first time at 2 weeks, kitties at 3 weeks. Regular faecal samples are then useful.

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