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 bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant- parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a br ...

s that infect

canid Canidae (; from Latin, ''canis'', "dog") is a family (biology), biological family of dog-like carnivorans, colloquially referred to as dogs, and constitutes a clade. A member of this family is also called a canid (). There are three subfamily, ...

s and

felid Felidae () is the family of mammals in the order Carnivora colloquially referred to as cats, and constitutes a clade. A member of this family is also called a felid (). The term "cat" refers both to felids in general and specifically to the ...

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 ''Toxocara canis'' (also known as dog roundworm) is a worldwide-distributed helminth parasite of dogs and other canids. The name is derived from the Greek word "," meaning bow or quiver, and the Latin word "caro," meaning flesh.Bassert , J., & T ...

'', which infects dogs. *'' Toxocara cati'', which infects cats and lacks intermediate hosts. *'' Toxascaris leonina'', which infects mostly cats, but also dogs. *'' Toxocara malayasiensis'', 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 organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

and

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side ...

Eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

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 Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and con ...

, 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 it is almost exclusively ...

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 uses a solid-phase type of enzyme immunoassay (EIA) to detect the presen ...

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), also known as a veterinary surgeon or veterinary physician, 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, vet ...

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.

Treatment

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

albendazole Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, ...

mebendazole Mebendazole (MBZ), sold under the brand name Vermox among others, is a medication used to treat a number of parasitic worm infestations. This includes ascariasis, pinworm infection, hookworm infections, guinea worm infections, hydatid diseas ...

, 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 (WBCs) and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. A ...

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