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What Is Paratenic Host, Parasitology | Parasitology Microbiology

The Fish As a Paratenic Host

Paratenic host

The estuarine turtle is a common host of the parasite Toxocara binucleatum. The fish is an intermediate host, and the snails are the parasite’s primary food source. This paper describes the biology of the fish as a paratenic host. It also discusses the differences between the two species. The eel can be either a paratenic or intermediate host.

The paratenic host is not required for the full life cycle of the parasite. The transfer host is an intermediate host that is not required for the completion of the parasite’s life cycle. During the life cycle, there are two types of hosts: the reservoir host and the paratenic host. The reservoir and the transfer host are both intermediate hosts. A reservoir is a host that has been infected by the parasite and serves as a source of infection for the latter.

The intermediate host is the second type of parasite. It is an intermediate host between two or more hosts. Unlike the definitive host, the intermediate host does not undergo developmental stages. Instead, it stays in an encysted or quiescent state until the opportunity arises to migrate to the definitive host. This is common for nematode parasites. This stage of development has no known biological significance, and is usually the result of a natural environment change.

The paratenic host is a possible intermediate host. It is the intermediate host between the definitive host. The intermediate hosts are also known as reservoir hosts. They are not required for the complete life cycle of the parasite, but they are still a potential host. The reservoir is an animal infected by the parasite, and it serves as a source of infection for humans. The transfer host is another form of intermediate host that is not required for the full life cycle of the parasite.

Type of host in parasitology 


Guinea pigs are carriers of B. procyonis. They contract the infection through the ingestion of eggs within the feces of raccoons (Baker 2007). After ingesting the eggs, larvae emerge and infiltrate the small intestines of the Guinea pig, then migrate through the liver into the lung and then disperse throughout the body through circulation. Larvae are then encapsulated and remain until they are eaten by an rodent.

Clinical Signs and Symptoms

No symptoms are evident in the guinea pigs because of B. procyonis, unless the organisms move into the brain. Migration may cause the symptoms of lethargy, tilting the head and ataxia. It could lead to stupor, cachexia hyperexcitability and torticollis, lateral recumbency or the opisthotonos (Van Andel and co. 1995).


In the cases where B. procyonis spreads into the cerebral cortex, a multifocal neutrophilic and eosinophilic infiltration are observed as well as malacia and perivascular lymphoid swelling (Van Andel and co. 1995). Eosinophilic granulomata have been observed within the lung of a few affected animals.


Histology is a diagnostic tool for B. procyonis (Baker 2007). The Baermann extraction method is employed to remove organisms from the brain tissues of animals in clinical trials (Van Andel and co. 1995).

Prevention and Therapy

Prevention, not treatment is the best strategy to B. procyonis control because clinical signs are usually not observed until the last stage of the disease and diagnosis is based on histopathology. The contamination of bedding and food by raccoon feces should be avoided. Ova is viable for many years in soil and can last for weeks to months in straw, and is resistant to the majority of disinfectants (Fox 2002). Cleaning of bedding contaminated with odours as well as the autoclaving process for caging could be necessary (Baker 2007). Humans, like the guinea pigs can contract infection from ingesting Raccoon feces. However, the transmission of raccoon feces from guinea-pigs humans is not possible (Fox 2002).).

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URL: https://www.sciencedirect.com/science/article/pii/B9780123809209000237

Pulmonary Parenchymal Diseases

O. Lynne Nelson, in Handbook of Small Animal Practice (Fifth Edition), 2008

Definition and Cause

Capillaria aerophila is an incredibly small nematode that is found beneath the epithelial surface of the airways that are large for cats and dogs.



Infection can be caused by the consumption of an ova or the host paratenic (earthworm).


Larvae move to the larger airways, and then live below the epithelial layer.


The parasite’s hypersensitivity is crucial for the clinical signs.

Clinical Signs


Signs are not common.


In rare cases, animals exhibit symptoms for allergies to asthma (cough).



Thoracic radiography could be normal or show an bronchial to bronchointerstitial pattern.


Eosinophilia in the peripheral region can be detected.


The secretions of the airways obtained through lavage of the bronchoalveolar system or tracheal rinse are analyzed to detect C. aerophila ova.


Fecal flotation can contain parasite ovathat can be confused with those from Trichuris Vulpis.

Differential Diagnostic


Chronic asthmatic bronchitis




Eosinophilic lung disease (nonparasitic)


Aelurostrongylus spp. in cats

Treatment and Monitoring


Fenbendazole can be given in the dose of 25-50 mg/kg BID every 14 days to pets and dogs.


Levamisole can be given in doses of 8 mg/kg SID PO for up to 20 days in dogs.


Ivermectin 400 mg/kg PO may be not used for breeds of dogs that are sensitive to ivermectin.


Pay attention to clinical signs and expect a positive prognosis.

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URL: https://www.sciencedirect.com/science/article/pii/B9781416039495500224

Nematoda (Roundworms)

Seppo Saari DVM, … Sven Nikander DVM PhD in Canine Parasites and Parasitic Diseases, 2019.

Life Cycle

The dog becomes infected after eating an egg that is infected or an animal that is a paratenic host e.g. the small rodent that has larval forms inside the organs. The infection is not transmitted transplacentally or through milk. Contrary to Toxocara, T. leonina does not move within the body of the final host. It instead develops in the mucosa of the small intestinal. Adult worms may be found within the intestine approximately six weeks after the infection. The period of prepatent is approximately 9 weeks. The eggs that are produced by the female enter the environment via the feces. If the conditions are right they will become infective quickly, usually within one week. After that, they could cause infection to the following definitive or paratenic animal host.

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URL: https://www.sciencedirect.com/science/article/pii/B9780128141120000052

Toxocara and Toxocariasis

Timothy Wu, Dwight D. Bowman In Advances in Parasitology, 2020

3.2.1 Toxocara canis

Larval migrans in lamb is comparable to other hosts with paratenic alterations as well, with the lungs and the liver being the organs most affected (Aldawek and co. 2002). Schaeffler (1960) observed that the rate of migration was affected by the time of the sheep’s life, with little or no movement beyond the liver of yearlings but lambs of very young age showed migration to mesenteric lymphoma nodes, pancreas, the heart and lungs, kidneys and brain, as well as muscles at least four days after infection. Larvae were alive and without any obvious decrease in number for the entire duration of the study which lasted 12 weeks for yearlings and eight weeks for lambs.

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URL: https://www.sciencedirect.com/science/article/pii/S0065308X20300385

The Molecular Epidemiology of anisakis and anisakiasis. An Environmental and Evolutionary Path Map

Simonetta Mattiucci, … Giuseppe Nascetti, in Advances in Parasitology, 2018

5.2 Host Preference vs Intermediate/Paratenic Hosts

Currently, according to the those records concerning the intermediate/paratenic hosts identified for the nine species and two genotypes belonging to the genus Anisakis, we could assess that a total of teleost fish species and cephalopod species of the marine realm are involved in the life cycles of these parasites.

However, fish species differentially occur as intermediate/paratenic hosts among the so far known species belonging to the genus Anisakis. This is in keeping and the ecology that hosts of fish, the geographical distribution in Anisakis spp. and their cycles of life. Regarding the ecology of fishes in relation to the various ecosystems that they are a part of in the marine environment they can be demersal or pelagic fish. The first category includes species that are feeding and are found in open ocean and are mostly associated to the ocean surface. Demersal fish can be classified into two kinds: benthic fish that are strictly benthic that live and feed at seafloor and benthopelagic fish which affect migration within the water column above the sea’s surface (the demersal zone that is located above the benthic zones) and are feeding at the bottom as well as in the middle of the water.

The fish species that are the most active in the life cycle of species within Clade 1 (i.e. A. simplex (s.s.), A. pegreffii, and A. berlandi) are mostly of the pelagic benthopelagic, pelagic, as well as benthodemersal, domains. In fact three Anisakis species are abundantly found and are prevalent in benthopelagic and pelagic and demersal species from the Families Gadidae, Merlucciidae, Scombridae, Carangidae, and Salmonidae. They are also frequently been observed in species of bathydemersal like the Pleuronectidae. Demersal fish of the coastal waters are located on or near or on the continental shelf. In deep waters , they can be located on or near the slopes of the continental. There are many species of fish that are considered to be demersal, are a few, like the cod Gadus Morhua and the European hake M. Merluccius, as well as additional gadids (found infected by Anisakis spp.) that feed on benthopelagic as well as pelagic species. These organisms may also include crustacean invertebrates which also serve as the primary intermediate hosts for these species.

The dolphins of the ocean and coast within the Delphinoidea The primary definitive hosts of the Anisakis spp. are mostly linked to a pelagic as well as benthopelagic world. It is possible to conclude that the life-cycle of these three Anisakis spp. includes benthopelagic and pelagic food webs that are found in boreal arctic, temperate and austral temperate water bodies (Klimpel and co. (2011); Kuhn et al. (2011), 2016; Mattiucci et al. 2014a Mattiucci as well as Nascetti (2008)) and as part of their diverse zones and their distribution (Figs 8-11 as well as 12).

Similar to this, a route of transmission in a predominantly pelagic trophic network can be suggested within the development that of A. typica, which was discovered in the larval phase in reef-associated and pelagic Teleost species (Kuhn and al. 2013; Mattiucci et al. 2002) and adults in coastal and pelagic Delphinoidea of tropical and warmer temperate waters.

A low number of teleost species have so far been identified as intermediate/paratenic hosts of the two species so far included in Clade 2 (A. ziphidarum and A. nascettii); they mostly belong to demersal teleost species of the Families Merlucciidae, Carangidae, Scombridae, Oreosomatidae, Trachichytiidae, and Tichiuridae. In those hosts, fish species the two species do not occur. In fact the evidence for these fish species comprise of very small numbers of larvae that have been identified (N between 1 and 5) in the thousands of Anisakis species. However, a an abundance of high (hundreds of larvae) was observed in deep-sea squids like M. ingens which had larvae that were genetically similar to A. Nascettii. These findings may reflect the eating habits of their most definitive habitats (Section 5.1) which’s preferred predators are deep-sea squids. In turn, it appears to confirm the notion that, even though few data are available regarding the larval presence in both Anisakis species in oceanographic basin deep-sea biology could be evolving in the evolutionary strategy that is suggested by the distribution in A. ziphidarum, and A. Nascettii (Figs 11 , 12).

The three distinct species in Clade 3 is represented genetically (Mattiucci and Nascetti, 2008) and high-quality morphologically differentiated taxa, as compared with others Anisakis types (A. the physeteris, A. Brevispiculata, as well as A. paggiae) are mostly observed in bathypelagic and bathydemersal bathyosts. Yet, very little information is available regarding the existence of the three parasite species in squids and squidfish, which are likely to be the most appropriate hosts for paratenics throughout their lives (Figs 9-11 and 12).

The discovery of high frequency and parasitic burdens, with numerous larvae of A. the physeteris, A. brevispiculata, and A. paggiae, found in the stomachs of swordfish X. gladius in the Central Atlantic Ocean (Garcia et al. 2011, Mattiucci and. 2014b) and the presence of squid beaks within that species of fish is in line with the findings of thousands of A. the physeteris found in sperm whales, which contained in addition to hundreds of cephalopods’ beaks in their stomachs (Section 5.1). These results suggest that parasites have developed methods to prolong their lives through a bathypelagic food chain that is likely to include squid more than fish in all oceanographic basins that are part of the geographic ranges of their host species (Figs 11 and 12).).

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URL: https://www.sciencedirect.com/science/article/pii/S0065308X17300593

Risks and diseases

P. Dekumyoy, … J. Waikagul in Encyclopedia of Food Safety, 2014

Clinical Signs and Symptoms

Gnathostoma larvae may wander around randomly in all organs of the paratenic host which includes humans. The illness has been classified into two broad categories, an external or superficial gnathostomiasis and visceral or internal gnathostomiasis. These are based on the location of larval migration as well as organs that are affected. The symptoms of the disease may be ocular, cutaneous neurological, or even a mix of these, and the presentation is varying from 24 hours to 2 years following the ingestion of larvae infected. The symptoms can be varied and include malaise or fever according to the location from the worm. The most useful signification for diagnosing a condition is a localized, intermittent swelling that migrates in the surface areas of the skin according to the depth of the affected skin in the instance of the arms, hands shoulder, feet, face or the the trunk (especially stomach) and sometimes in more vulnerable areas like the eye, the brain or spinal cord. The size of the swelling can vary and may be associated with indications of redness, inflammation, the formation of erythematous plaques that are indurated, as well as itching and pain, which could be the reason for panniculitis, eruptions that migrate and pseudofurunculosis. Additionally, the swelling is non-pitting and hard and lasts for different periods of time before subsiding. The swelling reappearing at a different site can occur after a period of symptom-free time between one week and several months. The most obvious signs of pleura-pulmonary dysfunction include frequent coughing, with or without hemoptysis or exudates and the chest, pain or dyspnea and pneumothorax, due to the effect of the respiratory system. Patients may experience epigastric pain, nausea or vomiting. These could be due to the an infiltration into the gastric wall due to parasites that they eat; granulomas can be found in the peritoneal space. Hematuria can occur and without or with pain or irritation to the kidneys. Severe symptoms, like seizures, paralysis, or comas, could be observed, based on the position of the worm’s location in the central nervous system (CNS). Ocular involvement is also a possibility most likely due to the movement of the worm through the optic nerves. This causes uveitis, pain inflammation of the intraocular space, bleeding, retinal scarring detached retinas, decreased visual acuity and even blindness. The clinical signs and symptoms observed during physical examination vary depending on the region of the body in the worms move and can vary between causal Gnathostoma species. For G. spinigerum as well as G. binucleatum it is a chronic condition that causes the possibility of relapse over a period of time in the aforementioned deeper region of the skin in the peripheral portion in the human body. For G. hispidum G. Nipponicum as well as G. doloresi diseases in which the migration occurs close to the area of the trunk, and accompanied by skin lesions, the condition can disappear on its own within 3 months without treatment.

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URL: https://www.sciencedirect.com/science/article/pii/B978012378612800144X

Digestive System, Liver and Abdominal Cavity

Randolph M. Baral, … Randolph M. Baral as seen in The Cat, 2012

Life Cycle

Hookworm infections can occur following the ingestion of drinking water or food that is contaminated with hookworm larvae, or eating paratenic hosts that have been infected. The larvae can live for months within cells of parasites hosts.14 Infection can also be seen when larvae migrate via the skin. In both cases the worm grows within the small intestine.14 Contrary to the dogs, transmammary infections have not been documented in cats.3,14

The time between the prepatent is between 19 and days, based on the method of infection. The time from infection to patency after the transcutaneous infected is more time-consuming than direct colonization. Infective L3 larvae grow between 2 and 7 days following the time when the ova have passed.3

Paratenic hosts do not require a definitive host to complete the parasite life cycle. Some parasites have a paratenic host that can serve as a reservoir. A reservoir host is an animal infected with a parasite and serves as a source of infection for humans. Although it is not always necessary for the complete life cycle of a paratenic host, it is often necessary for the larva to reach the reproductive stage of the parasite.

A paratenic host is an animal that does not allow the parasite to develop. In contrast, a reservoir host is an animal that is infected by the parasite and serves as a reservoir for humans. This type of host is also known as an accidental or transition host. In most cases, the paratenic hosts are not a part of the definitive host’s food chain. This is because the latter is more likely to survive extreme environmental conditions, such as the extreme temperature of the ocean.

In contrast, the paratenic host may have several functions. It may be the intermediate host of a parasite. It may be a host for intermediate parasites and the larvae of a parasite. The intermediate host may feed on the infected intermediate host. It is also a host for the adult forms of the parasite. However, the worms can only live in a single species of vertebrates.

A paratenic host is an animal that is a second-stage host. The parasite will move to a definitive host when it has enough food to do so. This can occur when an infected paratenic host is infected with the toxocara worm. Toxocara can cause gastrointestinal problems, which may include a variety of symptoms. It is important to identify the species of the infected animal to prevent the spread of infection.

Toxocara canina infects all canids and felids. The parasite is most common in kittens, but can be found in dogs and cats. Its range includes many different species of animals, including humans. Its natural habitat is primarily zoological gardens and zoos, where Toxocara leonina can be found. The species is a major factor in global climate change and human health.

Among the helminths, Toxocara canis is the most common. It is widespread in dogs and can be fatal in humans. It is present in well-developed and developing countries. It is most common in young children. There are many species of this parasite, but Toxocara canis is the only one that is able to cause human disease. It is an important public health issue in the United States.

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