The Toxocaridae are a

zoonotic A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a virus, bacterium, parasite, fungi, or prion) that can jump from a non-human vertebrate to a human. When h ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

s that infect

canid Canidae (; from Latin, ''canis'', "dog") is a family (biology), biological family of caniform carnivorans, constituting a clade. A member of this family is also called a canid (). The family includes three subfamily, subfamilies: the Caninae, a ...

s and

felid Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ). The 41 extant taxon, extant Felidae species exhibit the gre ...

s and which cause toxocariasis in humans ( visceral larva migrans and ocular larva migrans). The worms are unable to reproduce in humans. Notable species include: *'' Toxocara canis'', which infects dogs. *'' Toxocara cati'', which infects cats and lacks intermediate hosts. *'' Toxascaris leonina'', which infects mostly cats, but also dogs. *''

Toxocara malayasiensis The Toxocaridae are a zoonotic family (biology), family of parasitic nematodes that infect canids and felids and which cause toxocariasis in humans (visceral larva migrans and ocular larva migrans). The worms are unable to reproduce in humans. ...

'', which infects cats. *'' Toxocara vitulorum'', which infects buffalo and cattle.

Infection

Infection by ''T. canis'' or ''T. cati'' can cause various clinical manifestations. One of these is visceral larva migrans, wherein the larvae are unable to develop in humans as they do in cats and dogs, their natural hosts. Arrested development leaves the larvae to wander aimlessly in the body, causing inflammation, most commonly in the

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

and

lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

s. Eggs are introduced into the body through ingestion. This can occur when eggs are deposited on the hands or face, after handling infected dogs or cats. In some cases, they can also get them from undercooked meat. In children without exposure to animals, eggs can be introduced by directly ingesting egg-contaminated soil while playing in a yard or on a playground. Usually, the scenario involves a young child with a new puppy. Unfortunately, many young children who have been infected with these larvae, causing ocular larva migrans in the

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

, have been misdiagnosed to have

retinoblastoma Retinoblastoma (Rb) is a rare form of cancer that rapidly develops from the immature cells of a retina, the light-detecting tissue of the eye. It is the most common primary malignant intraocular cancer in children, and 80% of retinoblastoma cas ...

and have had their eyes erroneously removed.

Diagnosis

Direct identification of larvae in human disease is not feasible, so the diagnosis relies on history supported by serologic

ELISA The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay is a solid-phase type of enzyme immunoassay (EIA) to detect the presence of ...

assay. The most sensitive assay, called excretory/secretory (E/S), contains 96 immunogenic antigens isolated from cultured ''T. canis'' larvae.

Prevention

A number of products supplied by

veterinarian A veterinarian (vet) or veterinary surgeon is a medical professional who practices veterinary medicine. They manage a wide range of health conditions and injuries in non-human animals. Along with this, veterinarians also play a role in animal r ...

s can prevent or treat infections with this parasite. A great deal of information on this subject can be found on the computer sites maintained by the

Companion Animal Parasite Council The Companion Animal Parasite Council (CAPC, commonly pronounced "Cap-Cee") is a non-profit organization (501c3) composed of practicing veterinarians, academic veterinary parasitologists, veterinary technicians, state public health veterinarians, ...

Treatment

Visceral toxocariasis in humans (or dogs) can be treated with antiparasitic drugs such as

albendazole Albendazole is a broad-spectrum antihelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, hookworm infection, trichuri ...

or mebendazole, usually in combination with anti-inflammatory medications. Treatment for ocular larva migrans is to kill the larvae with a laser to prevent further damage, although some loss of vision in the affected eye is irreversible.

Association with asthma

Infection with ''Toxocara'' has been shown to stimulate

atopic Atopy is the tendency to produce an exaggerated immunoglobulin E (IgE) immune response to otherwise harmless substances in the environment. Allergic diseases are clinical manifestations of such inappropriate, atopic responses. Atopy may have a ...

disease, specifically asthma.Holland, Celia, and H. V. Smith. Toxocara: The Enigmatic Parasite. Wallingford, UK: CABI Pub., 2006. Print. Infection with this parasite causes asthma-like symptoms such as accumulation of

eosinophil Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. Along wi ...

s, an inflammatory response, and production of IgE, the immunoglobulins associated with allergic responses. People with asthma are shown to have a higher prevalence of ''Toxocara'' seropositivity.Cobzaru, RG, C. Rîpă, MM Leon, MC Luca, A. Ivan, and M. Luca. "Result Filters." National Center for Biotechnology Information. U.S. National Library of Medicine, 2012. Web. 02 Oct. 2016. Research suggests that the IgE production stimulated by infection with ''Toxocara'' may contribute to the onsets of allergic asthma in children. The effects of how parasite load, frequency of exposure, and influence of genetics affect this relationship between ''Toxocara'' infection and allergic asthma are still unknown, yet important in understanding how to prevent asthma and other atopic diseases around the globe.

References