Roundworm Infections in the Dog

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Nematode infections of the dog - the infection ( infection , also Infestation ) of dogs with parasitic living nematodes (Nematoda) - besides the tapeworm infestations and infections with protozoa ( giardiasis , Neosporose ) common parasitic diseases in veterinary practice. As so-called endoparasites ("internal parasites"), roundworms colonize various internal organs - most of them the digestive tract - and the skin. So far, around 30 different types of roundworms have been detected in domestic dogs; they can essentially also be found in wild dog species . The majority of these, however, often cause little or no symptoms in adult animals. The infection does not necessarily have to manifest itself in a worm disease ( helminthosis ). For most roundworms, infection can be detected by examining the feces for eggs or larvae. In Central Europe, infestation with dog roundworm and dog hookworm is of particular importance in terms of health policy , as they can also spread to humans ( zoonosis ). Regular deworming can significantly reduce the frequency of infestation and thus the risk of infection for humans and dogs.

The dog roundworm Toxocara canis - a parasite that also spreads to humans. For size comparison, a coin with a diameter of 23 mm.

Parasitosis of the digestive tract

Roundworm infestation

Life cycle of T. canis

There are two types of roundworms in dogs : Toxocara canis and Toxascaris leonina .

T. canis is an 8 to 18 cm long roundworm that parasitizes (lives as a parasite) in the small intestine . There, the adult females give off roughly 85 µm large, ungrooved eggs, the shell of which is thick and rough (golf ball-like) and which get into the outside world through the excrement. The period from infection to oviposition ( prepatence ) is three to six weeks, depending on the route of infection and the age of the dog. T. canis does not need an intermediate host for development , but the dogs can be infected via collective hosts such as rodents and birds . In collective hosts (paratenic hosts) there is no complete development cycle of the parasites, but multiple infections can accumulate in them infectious stages. In principle, there are three possible infection routes for T. canis : Peroral infection and the transplacental and galactogenic infection, which is much more common in puppies .

T. canis eggs
  • The peroral infection (infection by mouth) is carried out by recording of eggs from the environment or from larvae from collecting hosts. The worm eggs are only infectious about two weeks after they are excreted in the feces in the outside world. During this time, the second larval stage (larva L2) develops within the egg shell , which - like larvae from collecting hosts - is released during digestion in the small intestine of the new host. These larvae pierce the intestinal wall and reach the liver via the portal vein , where they develop into larvae L3. This travels through the bloodstream to the lungs , where it is coughed up and swallowed again. Only now molt the larva to the adult worms. As they migrate through the body, the larvae can also get into other organs, especially the skeletal muscles, and cause tissue destruction there. Often, however, they also form persistent stages in the tissue (stages in which the larvae persist in the tissue), which are important for the other two infection routes.
  • In the case of transplacental infection (infection via the placenta ), the persistent larvae L3 migrate from the uterus through the placenta and infect the unborn puppies in the womb.
  • The galactogenic infection (infection via the mother's milk) of the puppies occurs through excretion of the roundworm larvae that persist in the mammary gland in the mother's milk during the suckling period.
embryonated and thus infectious eggs of T. canis
Egg from T. leonina

T. leonina is 6 to 10 cm long, the eggs are about 80 µm in size and have thick shells. In contrast to the eggs of T. canis , they have a smooth surface. Infection occurs perorally through ingestion of food contaminated (contaminated) with eggs or through collecting hosts such as rodents, birds, reptiles or arthropods . The prepatency is 7 to 10 weeks.

In a German study, T. canis was detected in a frequency ( prevalence ) of 22.4%, T. leonina only in 1.8% of domestic dogs. In Austria, T. canis was found to have a prevalence of 5.7% and T. leonina of 0.6%. Both roundworms occur worldwide. A Czech study shows great differences in the prevalence depending on living conditions: 6% of the dogs kept privately in Prague, 6.5% of the dogs in animal shelters and almost 14% of the dogs from rural areas were infected with T. canis . In addition, an increase in the prevalence in autumn was shown. Domestic dogs in Belgium showed a mean infection rate of 4.4% for T. canis , those from larger kennels of up to 31%. In domestic dogs in Serbia T. canis was detectable in 30% of the animals, in herding and hunting dogs in Greece in 12.8% and T. leonina in 0.7% of the animals. In Canada, T. canis was found to have a prevalence of 3.9% and in the northeastern United States of 12.6%. In Australia T. canis was found in 38% of domestic dogs, in animals within the first year of life even in 73%. In Brazil, T. canis was found in around 9% of domestic dogs, in Thailand in 7.4%. In Nigeria, T. canis was observed in a frequency of 9%, T. leonina only in one of 0.6%, in Gabon 58.5% of domestic dogs were infected with T. canis . In wolves that live in the temperate climate zone, however, T. leonina is the most common intestinal nematode (prevalence 74%). Investigations on the red fox in southern England showed a prevalence of 56% ( T. canis ) and 1.5% ( T. leonina ), in Denmark of 59 and 0.6%. Foxes thus represent a natural reservoir of pathogens .

While the infection with T. leonina only very rarely causes clinical symptoms such as diarrhea, the disease-causing ( pathogenic ) effect of T. canis is significantly stronger. Puppies have a poor general condition, shaggy fur, stunted growth, alternating diarrhea and constipation , a distended stomach (“worm belly”) and anemia . Complications of T. canis infestation, some of which are fatal, include intestinal obstruction due to a ball of worms, rupture of the small intestine , pneumonia , liver inflammation or neurological symptoms due to stray wandering larvae in the central nervous system .

The diagnosis of worms in vomit can be made without special examinations. Roundworm infestation can be detected with relative certainty by microscopic evidence of the eggs released from the faeces using the flotation process, but only after the prepatent period has expired.

Hookworm infestation (ankylostomyasis)

A. caninum on the intestinal mucosa
Egg of A. caninum

There are two main hookworm species in dogs : Ancylostoma caninum and Uncinaria stenocephala . They parasitize in the small intestine and, by sucking in blood, cause anemia and damage to the intestinal mucosa . The worms have with about 5-15 mm only about a tenth the length of roundworms, a hook-shaped angled front end (hence the name "hookworm") and a large mouth capsule with cutting plates.

Females of A. caninum give eggs about 65 × 40 µm in size, which when laid, already show 4–10 stages of cleavage . They are oval and thin-skinned and get into the outside world through the faeces. The prepatency is two to four weeks. The larvae released from the eggs can bore their way through the skin into a new host ( percutaneous infection ) or be ingested orally - mostly via foraging hosts such as rodents. As with T. canis , the puppies can also be infected through breast milk ( galactogenic infection ). The larvae, which are dormant in the mammary gland, can be excreted after a single infection of a bitch over a period of up to three suckling periods.

The eggs of U. stenocephala resemble those of A. caninum , but have a larger longitudinal axis of 85 × 45 µm. Infection occurs exclusively through the peroral ingestion of larvae via contaminated food or collection hosts.

An infestation frequency of 8.6% was determined in Germany, 0.1% for A. caninum and 0.2% for U. stenocephala in Austria . A Czech study determined a prevalence of 0.4% each for both hookworms, a Greek study of 2.8% together. In studies on domestic dogs in Serbia and Nigeria, hookworms were found in a quarter of the domestic dogs examined, but U. stenocephala only in 0.4% of the animals. In Gabon, both hookworms were detectable in 35% of domestic dogs. In Canada, A. caninum was found in only 1.3% of domestic dogs, compared to 12% in the northeastern United States. In a Brazilian study (37.8% of domestic dogs) and a Thai study (58.1% of domestic dogs) A. caninum was the most common nematode of all. U. stenocephala has a prevalence of 26% in Australia . In wolves that colonize tundra , U. stenocephala is the most common intestinal nematode (prevalence 45%). This parasite is also very common in red foxes, with an incidence of 68%.

While the infestation with U. stenocephala often only causes minor symptoms such as diarrhea, the infestation with A. caninum can cause severe clinical pictures , especially in puppies. Bloody diarrhea, severe exhaustion and anemia can occur, sometimes with an acute or peracute course and sudden death. In the case of a chronic course, the young animals lag behind in growth, are listless, show poor appetite, diarrhea and emaciation. Pneumonia caused by migrating larvae is rather rare. A hookworm infestation can be diagnosed by detecting the eggs in the feces using a flotation method.

Whipworm infestation (trichuriasis)

Life cycle of T. vulpis
Eggs of T. trichiura (left) and T. vulpis (right)

The most common whipworm the dog is Trichuris vulpis . It is 4–8 cm long, has a long thin front and a thickened rear end. The eggs are lemon-shaped, 80 × 40 µm in size, brownish, thick-skinned and have thickenings ("pole pods") at the poles. They are not fearful when they lay their eggs. Infection occurs through ingestion of the eggs embryonating (containing a larva) in the outside world. The prepatency is relatively long at 9-10 weeks. T. vulpis parasitizes in the appendix and colon .

T. vulpis is distributed worldwide. In Germany around 4% of domestic dogs are infected, in Austria 3.1%. In the Czech Republic a prevalence of around 1% was determined, in Greece of 9.6%. In a study on domestic dogs in Serbia, however, T. vulpis was the most common intestinal parasite and was found in 47% of the animals examined. In the northeastern United States, 15% of domestic dogs were infected. In Nigeria, it was found in only 0.5% of the animals in one study, in another study it was significantly more common, in Gabon 50% of the domestic dogs were infected. In Brazil the infestation rate was 7%, in Thailand 20.5%. In Australia, T. vulpis was the most common roundworm in adult dogs, with a prevalence of 41%. The incidence of infestation in the red fox is 0.5%.

The disease-causing effect of T. vulpis is moderate. Affected dogs show diarrhea that is bloody and, if the course is less severe, with mucus. The animals lose weight, young animals lag behind in growth, and anemia can develop in the event of severe infestation. A reliable diagnosis can only be made via detection in the faeces using the flotation method.

Dwarf threadworm infestation (strongyloidiasis)

Infection with the dwarf threadworm Strongyloides canis can occur through ingestion of infectious larvae through breast milk, orally or through active penetration of the larvae through the skin. Autoinfection, i.e. infection of the same animal by larvae it excretes, is possible. S. canis parasitizes in the small intestine. The eggs are about 50 µm long and contain the infectious larva when excreted with the faeces. A prevalence of 1.8% was found for Greek herding and hunting dogs, and 2% for domestic dogs in Thailand.

Strongyloidiasis causes acute to chronic diarrhea in puppies, and occasionally constipation. The diagnosis can be made by detecting the eggs in the feces using a flotation method.

Stomachworm infestation

Stomach worms ( Physaloptera spp.) Belong to a genus of roundworms that is widespread worldwide and can attack the mucous membrane of the stomach and duodenum . Male worms are up to 30 mm long, female up to 40 mm long. The eggs are oval, thick-shelled, 55 × 32 µm in size and already contain a larva. The larvae form cysts in various insects - beetles , cockroaches and crickets in particular are intermediate hosts. Mice and frogs can also infect the dog as collection hosts. The larvae hatch in the stomach, attach themselves directly to the mucous membrane and molt to form adults (sexually mature worms).

The stomach worms cause damage to the lining of the stomach , resulting in gastritis , bleeding, and chronic vomiting. Heavy infestation leads to weight loss and anemia. The detection of the eggs in the feces with the flotation method is uncertain, as they hardly float. Therefore there are no systematic studies on the frequency of occurrence. A reliable diagnosis can be made using gastric lavage samples or a gastroscopy .

Esophageal worm infestation

The esophageal worm ( Spirocerca lupi ) is a bright red worm that leads to nodules in the esophageal wall. Male worms measure about 40 mm, female worms are about 70 mm long. Infection occurs perorally via intermediate hosts (various dung beetles ) or via paratenic hosts such as chickens, reptiles and rodents, which have become infected by eating the beetles. The larva migrates through the wall of the aorta , where it remains for about three months, and from there into the esophageal wall , where it develops into an adult worm. The prepatency is five to six months. The eggs are cylindrical in shape, have rounded caps, a thin, smooth wall and measure 30–37 × 11–15 µm. At the time of excretion, the larva is already in them.

The infection is common in the southern United States as well as in tropical countries. In Gabon , the parasite was found in a quarter of domestic dogs.

The worms can occasionally cause an aortic aneurysm during their migration , but the affected dogs are often asymptomatic. In the esophagus itself, S. lupi causes a granulomatous tissue reaction which, if left untreated, often degenerates and then forms various malignant tumors . In addition to squamous cell carcinoma and fibrosarcoma , the esophageal cells can also degenerate into osteosarcomas . The tumor-related mass in the chest can also lead to hypertrophic osteopathy .

An infestation is diagnosed by an endoscopy. This shows a mass in the esophagus with parasites on the wart-like openings. The diagnosis can be confirmed by the detection of embryonated eggs in the feces.

Liver hairworm infestation

The liver hairworm Capillaria hepatica occurs mainly in rodents and rabbits , infections in dogs are rare. The infection occurs by eating the liver of a rodent. Clinically, symptoms such as abdominal discomfort and liver enlargement occur, which are caused by the migration of the larvae through the liver and the laying of eggs. A reliable diagnosis is only possible through a liver biopsy .

Parasitosis of the respiratory tract

Lung hairworm infestation (Capillariasis)

Lung hairworm in the windpipe of a fox (bar = 1 mm)

The lung hairworm ( Capillaria aerophila , Syn .: Eucoleus aerophilus ) is up to 25 mm long and parasitizes in the lower airways . The eggs produced by the female worms have two pole pods and a colorless to greenish, granular shell. They get into the gastrointestinal tract by coughing up and swallowing, and finally into the environment via the feces. Infection occurs through ingestion of food or water contaminated with eggs. The larvae hatch in the intestine and enter the lungs via the bloodstream. The prepatency is about 40 days.

In Germany, an infestation rate of 2.3% was determined in domestic dogs, in Austria of 0.2%, in the Czech Republic of 0.6% and in Canada of 0.3%. In red foxes in southern England, a prevalence of 0.2% was determined for C. aerophila , whereas in Denmark it was 74%, making lung hairworms one of the most common roundworms and foxes an important natural reservoir for the infection of dogs. Other predators such as wolves, raccoon dogs, marten-like, lynx and cats are also attacked.

The lung hairworm infestation rarely causes clinical symptoms such as coughing, sneezing and nasal discharge. In the case of secondary bacterial infection, however, fatal bronchopneumonia can also occur. The diagnosis can be made by examining the faeces using a flotation method for eggs or by performing a lung biopsy .

Lungworm infestation

The lungworm Crenosoma vulpis is up to 1.6 cm long and is transmitted indirectly by eating from intermediate hosts such as snails . It colonizes the windpipe and bronchi. The main host is the red fox , but dogs, raccoon dogs, wolves and coyotes are also attacked.

C. vulpis was found in around 1% of domestic dogs in Germany, and in dogs with lung symptoms in 2.4 to 6% of animals. An infestation rate of 3.2% was determined in Canada. A prevalence of 17% was determined for red foxes in Denmark, and infestation rates between 25 and 50% in North America - the red fox can therefore be regarded as the natural main host.

Clinically, infection is characterized by a chronic cough and is similar to allergic bronchitis .

The detection of C. vulpis in faecal samples using the standard flotation method is relatively uncertain; only 28.5% of the faecal samples that were positive after the larval migration method also led to a positive result with the standard method.

Filaroididae

Filaroididae are a group of roundworms that parasitize on the lungs and trachea . The most common species are Oslerus osleri ( syn . Filaroides osleri ), which parasitizes the windpipe - especially in the area of ​​the tracheal fork (Bifurcatio tracheae) - and Filaroides hirthi , which attacks the lung tissue (filaroidosis). Male O. osleri grow to about 6–7 mm, females 10 to 13 mm. The eggs measure 80–120 × 60–70 µm, the larva L1 is about 250 µm long. F. hirthi is 2–3 mm (males) or 7–13 mm (females), the larva L1 is 240–290 µm long. Andersonstrongylus milksi (Syn. Filaroides milksi ) is a rare representative of the Filaroididae in dogs and largely resembles Filaroides hirthi in appearance, life cycle and clinical picture .

The parasites cause small nodules in the area of ​​the branching of the windpipe or in the lung tissue; dead worms can also cause larger granulomas . The female worms lay eggs from which the larvae hatch, which develop into adult worms over five moults. The infection occurs either via eggs or the first larva, mostly via direct contact with saliva, nasal secretions or via regurgitated stomach contents when the puppies are fed by the mother. Infection through eating feces is possible, but rare. Infected animals can also self-infect because the worms do not need an intermediate host. When infected, the larva migrates from the intestine via blood or lymph vessels into the bloodstream, from where it gets into the lungs or tracheal wall and develops into an adult worm. The prepatency for O. osleri is ten weeks, for F. hirthi five weeks.

The representatives of the Filaroididae occur worldwide. O. osleri is particularly widespread in foxes and other canines living in the wild, infections in domestic dogs are rare. F. hirthi was first observed in dogs of the Beagle breed in the USA, but now occurs worldwide and also in other dog breeds, especially in Beagles kept as laboratory dogs.

The infection with O. osleri causes chronic inflammation of the trachea and bronchi with a strong dry cough and abnormal breathing noises when inhaled. The disease usually only manifests at the end of the first year of life and does not respond to antibiotic treatment. The simultaneous appearance of similar symptoms in the mother and her pups is an indication of such an infection. Occasionally an attack-like shortness of breath can occur during exercise . Fever usually does not occur.

For diagnosis, the detection of nodules by means of a lung specimen , possibly also on X-ray images of the chest , as well as the larvae in lung lavage fluid or tracheal swabs can be used. The detection of larvae in the faeces by means of the flotation method is uncertain, especially since the larvae are only excreted in the faeces irregularly, and not at all during the relatively long prepatency.

Parasitosis of the bloodstream

Heartworm infestation (dirofilariasis)

Dog heart with heartworms

The pathogen of the disease is Dirofilaria immitis , a nematode 1 mm thick and 20–30 cm long. It needs an intermediate host for its development, part of the development cycle - from larval stage L1 to L3 (microfilariae) - takes place in mosquitoes . The transmission to the dog takes place during the sucking act. The larvae L4 develops in the subcutis and penetrates the bloodstream and sheds its skin there to become the adult worms. The adult heartworms colonize the right half of the heart , the pulmonary vascular trunk and the sections of the vena cava near the heart . Only about six months after infection do the females again form microfilariae (larvae L1), which enter smaller blood vessels with the blood and are ingested again by mosquitoes when they suckle.

So far, over 70 mosquito species have been identified as carriers, but none of them are native to Central Europe. In Turkey, 26% of domestic dogs have antibodies against D. immitis ( seroprevalence ). Seroprevalence is 4% in the southern United States and 1% in the northern states. In the Australian state of Victoria, antibodies against D. immitis were detected in 8% of dogs over two years of age, in South Korea the seroprevalence is around 40%.

Infested animals show reduced performance as the mature worms develop, i.e. only about six months after infection, and tire quickly. Right heart failure develops with overload and enlargement of the right side of the heart ( cor pulmonale ), which manifests itself in shortness of breath, coughing and the formation of edema . Liver and kidney failure can also occur as a result of heart failure .

The serological detection of D. immitis antigen , which is highly specific and sensitive , is preferably used for diagnosis . In addition, microfilariae can be detected microscopically by means of a blood test with enrichment or occasionally with a simple blood smear . However, this evidence is limited to the phases in which microfilariae are actually present in large numbers in the blood, which is why they are viewed as less sensitive due to many false-negative findings.

Angiostrongylosis

The French heartworm ( Angiostrongylus vasorum ) is a parasite of the pulmonary vascular trunk, the pulmonary arteries and the right ventricle . The very thin (170–360 µm), pink worms are 1.4 to 2 cm long. The prepatency varies between 35 and 60 days. The main final hosts of the parasite are foxes, but dogs, wolves, coyotes, badgers, pampas foxes, Brazilian foxes, crab foxes and small pandas are also infested. Originally, the parasite was mainly found in France, Denmark and Great Britain. The frequency of infestations has increased significantly worldwide for several years, so there are also endemic herds in the United States, South America, Australia and in the Asian part of Russia. The most recent figures in Germany show an infection rate of 7.4% in animals with a lung disease or 0.5% of the total dog population.

Female worms lay undifferentiated eggs, which enter the pulmonary capillaries via the bloodstream, where larvae L1 hatch and migrate to the lower airways. The larvae are coughed up, swallowed and excreted with the feces. The elimination period (patent) is up to five years. In intermediate hosts (different species of snail ) they develop into the infectious larva L3. After ingestion, the larvae penetrate the intestinal wall and develop in the lymph nodes of the abdominal cavity. Then they reach the right ventricle of the heart and the pulmonary arteries by blood route, where they molt to the adult worms.

The larvae reach the pulmonary arteries ten days after peroral infection and cause severe lung changes and blood clotting disorders to occur. Occasionally the worms and larvae also migrate to other organs ( larva migrans ).

Clinically affected dogs show a slowly progressive impairment of the heart and / or lung function. Chronic cough, shortness of breath, refusal to eat and weight loss, diarrhea, central nervous symptoms, and tissue bleeding are also common symptoms. The diagnosis is made by detecting larvae L1 in the faeces using the larval emigration method. The time-consuming larval migration process can be replaced by serological (sandwich ELISA) or PCR detection. A rapid test ( IDEXX Angio Detect ) is available for serological detection .

Parasitoses of the urinary organs

Giant kidney worm infestation

The giant kidney worm ( Dioctophyme renale ; Syn. Dioctophyma renale ) is the largest known parasitic nematode and can attack the kidney and occasionally the abdominal cavity in dogs . Female worms reach lengths of over one meter with a diameter of up to 12 mm; male worms measure 20 cm by 6-8 mm. Both sexes are blood red in color. The parasite is widespread worldwide, but is rare in Europe. It is not limited to the dog as the ultimate host, but can attack most mammals (including humans). Reproduction and egg excretion can only occur if the same kidney is infected by both a female and a male worm and the worms have already perforated the renal pelvis. Eggs are excreted in the urine through the renal pelvis . These eggs are oval to cylindrical, yellow-brown, thick-walled, with a rough, knobbed surface and 71–84 × 45–52 µm in size. The eggs embryonate within two weeks to three months, depending on the ambient temperature, and are then infectious to intermediate hosts.

Infection occurs via the consumption of intermediate hosts or paratenic hosts which contain cysts with larvae of the parasite. Intermediate hosts are earthworms and aquatic little bristles , in which the larva L1 hatches and develops into larva L3; Paratenic hosts are freshwater fish or frogs in which the larva L3 encapsulates itself in muscle meat. The larva is released from its cyst in the digestive tract of the final host, penetrates the intestinal wall and migrates to the liver for about 50 days . It then penetrates directly through the abdominal cavity into the kidney, where it develops into an adult worm. The right kidney is more often affected than the left. In dogs, however, the parasite quite often remains in the abdominal cavity, which has less serious consequences for the dog than an infestation of the kidneys. The infected kidney is slowly destroyed by the parasite, which usually also perforates the renal pelvis . Since eggs very rarely appear in the urine, their detection is unsuitable for diagnosis. A kidney worm infestation can be detected using sonography .

Urinary bladder hairworm infestation

The urinary bladder hairworm Capillaria plica is 13 to 60 mm long and colonizes the urinary bladder , occasionally the ureter and the renal pelvis. The eggs are 63–68 × 24–27 µm in size, covered and have a slightly roughened shell. They are excreted in the urine. Earthworms, in which the infectious larva L1 develops, serve as intermediate hosts. The infection occurs through the reception of the intermediate hosts or indirectly via collective hosts.

In the case of domestic dogs in larger kennels, up to three quarters of the animals can be infected. A prevalence of 80% was found in red foxes in Denmark, making urinary bladder hairworms the most common roundworms and foxes being an important natural reservoir for the infection of dogs.

C. plica rarely causes symptoms. If more severe, it can lead to an inflammation of the bladder with urination and urinary incontinence . The diagnosis can be made by detection in the urine, but not in animals younger than eight months due to the long prepatence.

Parasitosis of the skin

Peloderosis

Pelodera strongyloides (Syn. Rhabditis strongyloides ) is a normally free-living nematode that occurs worldwide in moist, putrid organic material and whose larva L3 occasionally attacks the skin of dogs. Infection occurs through direct contact with material containing larvae in damp and soiled berths (for example when using damp straw as litter). It is unclear whether the larvae can penetrate healthy skin; in any case, existing skin diseases and moist conditions that soften the skin favor the infection. The larvae parasitize on the hair follicles and the upper layers of the dermis .

The lesions are usually limited to those parts of the skin that were in direct contact with the infectious material, usually the abdomen, underbust and extremities. The affected skin is reddened, moderately to severely inflamed and partially to completely hairless. There is pronounced itching , which can lead to further skin lesions (crust formation) and secondary bacterial infections . Usually the disease is self-limiting, also because the dog is a false host for the worms . The diagnosis is made by scraping the skin , in which the larvae, measuring approximately 600 × 38 µm, can be easily recognized with the microscope.

Dracunculosis

Dracunculus insignis is a roundworm that occurs mainly in North America and whose main host is raccoons . The medina worm ( D. medinensis ) occurs in Asia and Africa and affects numerous mammals including humans. Both parasites are occasionally found in domestic dogs in these areas. Infection occurs perorally through ingestion of water with hoppers , which serve as intermediate hosts, or indirectly through ingestion of foraging hosts such as frogs. The larvae are released during digestion and burrow through the intestinal wall. Female worms migrate to the subcutis after mating. Here they form painful and partially fistulous pseudo cysts which rupture upon contact with water and release the about 0.5 mm long larvae. The diagnosis can be made by detecting the larvae or female worms in such cysts.

Cutaneous dirofilariasis

Dirofilaria repens is a subcutaneous tissue parasite in dogs. Mosquitoes act as intermediate hosts and carriers. It occurs mainly in southern, southern, eastern and western Europe as well as large parts of Asia, but is spreading further and further to northern Europe and is increasingly being detected in Germany.

The infestation with D. repens occasionally causes skin lumps, swellings, itching, abscesses and hair loss, but often runs completely without clinical symptoms. The acid phosphatase reaction can be used for diagnosis .

Rare filariasis

Acanthocheilonema reconditum (Syn. Dipetalonema reconditum ) occurs in the USA and southern Europe. The infestation rates in southern Italy are 16.5%, in Greece up to 8%. The cat and dog fleas serve as carriers. The worms parasitize mainly in the subcutaneous tissue, a small part of the parasites can also be found in internal organs.

Cercopithifilaria grassi (Syn. Dipetalonema grassi , Acanthocheilonema grassi ) occurs in southern Europe, in Greece around 1% of dogs are infested. The carrier is the brown dog tick . The larvae (microfilariae) parasitize the skin.

Dipetalonema dracunculoides (Syn. Acanthocheilonema dracunculoides ) occurs in Africa and Spain. In Africa, lice flies are the main carrier, in Spain, where the prevalence is 1.5%, the brown dog tick. The prepatency is 2–3 months.

Parasitosis of the eyes

Thelaciosis

The thelaziosis is caused by representatives of the genus Thelazia . They are whitish roundworms about 1.5 cm in length. Thelazia callipeda is particularly widespread in the Far East (Japan, China, Korea, India and Russia), but it is also a common cause of eye diseases in some regions of Italy with infestation rates of up to 60%. There have recently been an increasing number of individual cases in Switzerland and France. So far, four cases have been documented in Germany, three of them after a stay in Italy. Thelazia californiensis is common in California. The biology of these roundworms has not been conclusively clarified; flies are suspected to be the vector, which ingest the larva L1 and in which the development up to the infectious larva L3 takes place.

Thelacia parasitize on the eyeball under the nictitating membrane and in the tear ducts and cause conjunctivitis and increased lacrimation . Obstruction of the tear ducts or corneal inflammation can also occur. If the infestation is severe, the worms are already visible to the naked eye. A reliable diagnosis can be made by detecting the worms or their larvae in eye wash samples or a biopsy of the lacrimal gland .

Onchocerciasis

The causative agent of onchocerciasis in dogs is Onchocerca lupi . The disease occurs in North America and some European countries (Greece, Hungary) but is rare - 64 cases have been described so far. The worms cause pea- to bean-sized granulomatous nodules in the sclera , around the eyes and conjunctiva. Under certain circumstances a lymphoplasmacytic inflammation of the middle skin of the eye can develop. The diagnosis can be made by detecting the worms in the nodules.

Other parasitoses

Trichinella infestation (Trichinellosis)

Trichinella spiralis

Trichinae ( Trichinella spp.) Are a genus of roundworms whose larvae migrate into the skeletal muscles . Trichinae do not have an outside phase; the infection occurs through the consumption of raw muscle meat from an infected animal. In Europe, Trichinella spiralis is most widespread in domestic animals, and Trichinella britovi and Trichinella nativa are also found in dogs.

In the intestine, the muscle meat and cyst capsules are digested, releasing the larvae and invading the lining of the duodenum and jejunum . There they develop into adult trichinae within about four days. After mating, the female worms dig deeper into the mucous membrane and lay up to 1,500 eggs per individual over four to 16 weeks. The hatched larvae are approximately 100 micrometers long. They first migrate into the lymph vessels and then via the portal vein into the peripheral blood vessel system. As soon as they reach the muscles, they leave the blood vessel and dig into a single muscle fiber . There they grow rapidly to a length of 1 mm, encapsulate and begin to take on the typical curled shape. Capsule formation in muscle tissue begins around 15 days after infection and is completed after four to eight weeks - the host's meat is then infectious. The larvae can remain infectious in a host's muscles for years; they are most commonly found in the diaphragm , tongue , masticatory muscles and intercostal muscles .

Little data exist on the frequency of trichinae infestation in dogs. In Finland , which has a very high prevalence of Trichinae in wild animals, an infection frequency of between 4.9% and 8.6% was found serologically in dogs . In the same study, however, cysts in the muscles were found in only one of 102 dogs. In China, where dogs are slaughtered for human consumption, trichinae were found in an average of 16.2% of slaughtered dogs, with the prevalence varying between 1.2 and 44.8% depending on the region.

Raccoon roundworm infestation

Newly hatched raccoon roundworm larvae

The raccoon roundworm ( Baylisascaris procyonis ) is a relative of the dog roundworm ( Toxocara canis , see above), which specializes in raccoons as the ultimate host. In Germany, 70% of all raccoons are infected with the parasite. Infections of the dog as the ultimate host and egg shedder are known from the USA, their frequency tends to increase and represent a considerable risk of zoonosis . However, the infestation of the dog as a false host through ingestion of eggs is clinically more serious . The larva of the raccoon roundworm very often migrates to the central nervous system of the false host, where it causes severe neurological deficits that can be fatal.

Combat

Most infections are rather harmless for adult dogs, since a pathogen-host balance is established when the immune system is intact . However, since some of them can cause health disorders and some also represent a potential danger to humans, regular worming treatments for dogs are quite useful. There is a higher risk of infection, especially for dogs in larger holdings, young animals, dogs in contact with other animals, hunting dogs, strays and animals that are fed raw meat products. The European Scientific Counsel Companion Animal Parasites (ESCCAP) - the European association of experts on parasites in dogs and cats - has therefore issued recommendations for combating worm infections. These are adapted to regional characteristics by national veterinary specialist societies. Such guidelines also exist in the United States and are published here by the Companion Animal Parasite Council (CAPC).

The recommendations, last adapted in January 2008 according to the ESCCAP guidelines for Germany, aim to protect dogs “ ... against infections with worms and their consequences through professional diagnostics, therapy and prevention ”. Targeted control is recommended for roundworms, hookworms and heartworms.

Puppies should to from the age of two weeks every 14 days weaning be wormed prophylactically. Suckling bitches should also be treated the first time puppies are dewormed. A safe roundworm prophylaxis can only be achieved with monthly deworming. A monthly cycle is recommended by ESCCAP only for the above risk groups and dogs with close contact with small children. For the other dogs, it is advisable to deworm four times a year. An increase or decrease in the frequency of deworming can be done through an individual risk analysis and regular faecal examinations. In Germany, drugs based on emodepside , fenbendazole , flubendazole , mebendazole , milbemycin oxime , moxidectin , pyrantel and selamectin are approved for domestic dogs to treat roundworms . These drugs are broad spectrum anthelmintics and also have an effect against most of the other roundworms found in dogs. In addition, the manure should be collected every day and disposed of with household waste. Regular cleaning and disinfection measures and the flaming of the kennel floor ensure that the infectious eggs and larvae in the immediate vicinity are eliminated or at least reduced. No preparation is currently approved for the treatment of pregnant bitches, although experimental studies have shown that the use of selamectin or emodepside during pregnancy is effective in preventing infection in unborn puppies.

Heartworm control only plays a role in Central Europe for dogs that are to be brought to or come from the Mediterranean region. Moxidectin, milbemycin oxime and selamectin are currently approved for the therapy and prophylaxis of heartworm disease. In addition, protection with insect repellants such as permethrin or deltamethrin is recommended when traveling to heartworm endemic areas .

Dangers to humans

Humans are false hosts for the dog roundworm Toxocara canis and the dog hookworm ( Ancylostoma caninum ), that is, the larvae damage the infected organs, but they do not develop into adult worms. Both are the most important zoonotic pathogens among the dog nematodes in Central Europe .

Toxocara larva in a human liver

Infection with T. canis usually takes place via a smear infection through oral ingestion of soil contaminated with dog feces. Farmers, gardeners, sewer workers, veterinarians and small children (playing in the sandpit) are particularly at risk. In Austria, antibodies against T. canis were detected in 3.7% of healthy persons ( seroprevalence ), in 44% of persons in exposed occupations. In Slovakia, healthy blood donors from urban areas had a seroprevalence of 12% and those from rural areas of 17%. In the United States, 14% of the population is seropositive. An Egyptian study found a seroprevalence of 18% in healthy adults, and a similarly high infection rate was found in children from rural regions in China. In Jordan the seroprevalence is 11%, in Nigeria 30% and in rural Argentina 23%. However, these seroprevalences only indicate what percentage of the population has experienced an infection. Such an infection does not necessarily have to lead to a disease, but can be warded off by the immune system without any symptoms. In sandboxes in large European cities, contamination with worm eggs was found in 10–100% of the samples. Diseases occur mainly in children and adolescents. As visceral larvae ( Larva migrans visceralis ), the larvae of the dog roundworm can attack various organs and cause severe tissue damage there. The eyes , lungs , liver, and central nervous system are most commonly affected.

A. caninum larvae can penetrate the skin when walking barefoot over floors soiled with dog feces. There, as migrating larvae ( Larva migrans cutanea , "skin mole") , they cause extremely itchy reddening of the skin. The passages drilled by the larvae are often visible to the naked eye. The disease usually heals spontaneously, but this can take months. Infections of this kind are rare in Central Europe, but one of the most common skin diseases in tropical and subtropical regions. In addition, A. caninum can also cause intestinal inflammation with signs of an acute abdomen .

Of the filariae, the heartworm ( Dirofilaria immitis ) and Dirofilaria repens are zoonotic pathogens. D. immitis rarely causes disease in humans, although around 20% of the population in endemic areas have antibodies. Usually the larvae are encapsulated in the lungs. More than 400 cases have been described for D. repens , in Europe mainly in Italy and France. The seroprevalence in humans is 68% in Italy and 22% in France. The adult worms migrate mainly into the subcutaneous tissue, but they can implant themselves in all possible organs.

The dog only plays a role in the spread of trichinella in a few regions of the world. In China, the consumption of dog meat is an important source of infection for humans. Four cases of eye worm infestation (thelaciosis) have so far been described in humans in Italy and France, but the disease is particularly widespread among the poorer population in Asia. In addition, dogs can contribute to the spread of non-host-specific parasites such as the giant kidney or medina worm. However, the epidemiological significance of domestic dogs for human infections has not yet been investigated for these parasites.

literature

  • Johannes Eckert et al. (Ed.): Textbook of parasitology for veterinary medicine. Enke-Verlag, 2nd edition 2008, ISBN 978-3-8304-1072-0 .
  • Thomas Schnieder (Ed.): Veterinary Parasitology. Paul Parey, 6th edition 2006, ISBN 3-8304-4135-5 .
  • Peter F. Suter and Barbara Kohn (eds.): Internship at the dog clinic. Paul Parey, 10th ed. 2006, ISBN 978-3-8304-4141-0 .

Individual evidence

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