Toxocariasis (Visceral larva migrans, Ocular larva migrans and covert toxocariasis: Toxocara canis and Toxocara cati) -  IgG antibodies, molecular diagnosis  (PCR) and molecular identification of species (PCR and sequencing)


Information 04-11-2015.


Toxocariasis is a zoonotic infection caused by parasitic nematodes of the genus Toxocara, family toxocaridae. Toxocariasis may be mainly caused by the larvae of two species Toxocara canis and Toxocara cati, affecting dogs and cats, respectively, but could also be produced by the larvae of Toxocara malaysiensis (cats), Toxocara leonina (dogs, cats and other) and Toxocara vitulorum (cattle). Parasitism may affect people, with worldwide distribution, although its incidence is much higher in rural areas and tropical countries. People become infected by accidental ingestion of embryonated eggs from soil or contaminated food.


Both Toxocara canis and Toxocara cati, or other related species eliminate spherical brown eggs and 75 to 90 .mu.m, Parasites may be 4 to 6 cm (male) and 15 cm (female). These worms infect predators that often get infected when they ingest directly embryonated eggs or some intermediate hosts that may have ingested (earthworm, cockroaches, birds or rodents, in which the larvae hatched from the eggs will be found. The people become infected accidentally in common by ingesting embryonated eggs conditions. However, in some ways, may happen to become infected by eating meat undercooked cats, dogs, foxes, cows, monkeys, pigs, sheep, rodents , chickens, pigeons, ostriches, ...


The life cycle of Toxocara spp. It involves a host mammal where they mature and become sexually mature adults. In this host, embryonated eggs hatch releasing larvae ingested second stage (L2) in the small intestine. Subsequently, the larvae penetrate the wall of the small intestine and enter the bloodstream, which in its usual host leads them to the venous return to the right heart and lungs, where they exit apara migrate through the organs, usually the lungs, liver, brain and, in rare cases, the eyes. It is in these organs where larvae usually mature at the third Be the alveolar lumen, ascend trachea and pharynx to be swallowed and return to the small intestine, where they mature into adult males and females who copulate made egg laying. The eggs are excreted to the outside through the stool and become infective after several weeks outside the host under suitable humidity and temperature environmental conditions. Ideally, the eggs can mature infectious stage after two weeks outside a host and remain infectious for years because of their high resistance to the effects of chemicals and temperature changes.


Toxocara transmission. occurs through ingestion of embryonated eggs, each containing a fully developed larvae L2, sources contaminated with fecal matter. The spread of these microorganisms to foods or surfaces may occur for example through mechanical vectors such as flies that feed on faeces.


When embryonated eggs are ingested by a mammalian species other than their usual host, described biological cycle previously can not be completed, so the larvae, after passing through the intestinal wall can not find their their way back to the small intestine for mature adults and remain in circulation for several wandering organs and tissues. Physiological infection by Toxocara spp larvae reactions. They depend on the host immune response and the parasite load. In most cases infections are asymptomatic, especially in adult individuals. When symptoms are mild and the process is known as "hidden Toxocariasis" (Covert toxocariasis). This process is manifested by some of the following signs and symptoms: cough, expectoration, signs of bronchitis, asthma signs, fever, abdominal pain, headache, behavioral changes, difficulty sleeping, arthralgia, hepatomegaly or lymphadenitis. These signs and symptoms are the result of migration of larvae second stage (L2) through the body.


In cases where the parasitic load is high or repeated infections occur, these microorganisms can cause reaction parasitic granulomatosis level internal organs resulting in the process called visceral larva migrans (VLM: visceral larva migrans) or larva migrans ocular ( OLM: Ocular Larva migrans). The most prone to this infection people are those who may be exposed to embryonated eggs of Toxocara spp .: Children playing in contaminated homes or parks, or workers who exercise their profession in areas that might be contaminated as gardeners, farmers gardens, masons, or veterinarians, among others.


In the VLM, larval migration induces inflammation of internal organs and sometimes central nervous system. Symptoms vary depending on the affected organ. Patients may have pale skin, tiredness, weight loss, anorexia, fever, headache, rash, cough, asthma, chest tightness, increased irritability, abdominal pain, nausea and vomiting. In addition, in some cases it can be viewed routes subcutaneous migration of larvae. Patients commonly diagnosed with pneumonia, bronchospasm crisis, chronic pulmonary inflammation, hypereosinophilia, hepatomegaly, hypergammaglobulinemia (IgM classes, IgG and IgE) and leukocytosis. In rare cases the VLM is manifested as a box epilepsy, cardiac inflammation, pleural effusion, respiratory failure and death.


In rare cases, infection Toxocara canis and Toxocara cati, can affect the eye causing ocular larva migrans (OLM), characterized by granulomatous endophthalmitis and frequent injury to the eye and visible posterior pole in the fundus. In severe cases, the infection can cause inflammation of ocular tissues, retinal fibrosis, retinal detachment, retinal granuloma, parasitic cysts, peripheral granuloma, endophthalmitis with opacification of the vitreous humor, which can compromise vision and lead to blindness.


Recommended tests for diagnosis:


The diagnosis of human toxocariasis is based on detecting antibodies (ELISA), as it is typically positive in 100% of cases. Sometimes, in countries where parasitism by other helminths often results can be motivated by unspecific cross of induced antibodies with other helminthic antigens used in serological tests to detect antibodies Toxocara reactions. antigens. The most widely used antigen for serological tests are usually excreted toxocariasis-excreted antigens (TES: Excretory-Secretory Toxocara), obtained from cultures of larvae of stage 2 (L2) of Toxocara canis. They are currently using recombinant antigens to avoid cross - reactions in serological tests. Among these antigens are the rts-30, rts-120 and rts-26 antigens.

Observation of the larvae is occasional and requires removal from a fabric and it is not usual. Molecular diagnostics (PCR) diagnostic technique is also common for the same reason, and when applied to identify a larva is obtained in a tissue granuloma. Another situation application of molecular testing (PCR) has been to diagnose the presence of eggs producing species toxocariasis in feces of dogs or cats or contaminated with the stool of these animals soils.

Tests in IVAMI:


  • Detection of IgG antibodies by ELISA.
  • Molecular diagnosis (PCR), to identify larvae Toxocara spp. or Toxocara spp.

Recommended sample:


  • Detection of IgG: serum (0.5 to 1 mL).
  • Molecular diagnosis (PCR) to identify larvae of Toxocara spp .: Tissue biopsy.
  • Molecular diagnosis (PCR) to diagnose the presence of Toxocara spp eggs animal feces .: (dogs, cats, ...) or ground (earth).

Preservation and shipment of sample:


  • Refrigerated (preferred) for less than 2 days.
  • Frozen: over 2 days (for molecular diagnostic tests only).


Delivery term:


  • Detection of IgG (ELISA): 48 to 72 hours.
  • Molecular diagnosis (PCR): 24 to 48 hours.
  • Molecular diagnosis for species identification (PCR and sequencing): 72 to 96 hours).


Cost of the test:


Consult .