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Table 2 Diagnostic methods for toxocariasis

From: Toxocariasis: a silent threat with a progressive public health impact

Approaches

Methods

Characteristics

Targets

Advantages

Disadvantages

Direct microscopy [9, 13, 14, 133]

Biopsy and visual detection of the parasite

Invasive, insensitive and time-consuming

Larval sections or eggs

Widely available

Requirement of skilled technicians

Laboratory findings [13, 134, 135]

Blood biochemical analysis

Should be considered in combination with clinical manifestations and further laboratory confirmation

Eosinophilia (average counts of 10 000 cells/mm3, approximately 1500 cells/mm3in CT, normal range in OT or CT (< 500 cells/mm3) or eosinophil cationic protein (ECP) levels (designated as > 28 mg/L)

Useful for detection of active Toxocara infections

Non-specific

Antigen detection [13, 14]

Sandwich ELISA

Complex monoclonal antibody (MoAb) production

Circulating TES Ag

Useful for confirmation of active infection

Low sensitivity and specificity

Antibody detection

TES-Ag-ELISA

A standard test for VLM and OT in reference laboratories

Antibodies

Good sensitivity and specificity (70–100%) [4, 13, 14, 33].

Research laboratory use only

TES-Western blot (24, 28, 30 and 35 kDa fractions of TES Ag)

More specific, but less sensitivity than ELISA [33, 136]

 

Several commercially available kits in enzyme immunoassay, and Western-blot test formats (ELISA NOVUM, ELISA PU and Toxocara CHEK) [4].

Unavailable for discrimination of past and recent infection

Recombinant antigens

Less cross-reactivity with antibodies from other helminth infections in endemic regions where poly-parasitism is common, in contrast to TES-Ag [14].

rTES-30, rTES-26 or rTES-120 [67, 136]

Recommended as the best option for diagnosis of human toxocariasis [67, 137–139].

Nucleic acid amplification [9]

RFLP

Requires a large quantity of genomic DNA, which is not readily available for parasites of small sizes, particularly larvae and eggs

ITS-1

ITS-2

High sensitivity and specificity; useful for species identification and quantification of parasite burden

Technically demanding, requires skilled laboratory technicians

RAPD

Low reproducibility and specificity; cannot distinguish between eggs of T. canis and T. cati.

PCR

The risk of carry over contamination; low throughput of samples analysis

qPCR

Rapid and specific identification of T. canis and T. cati eggs in faecal and soil samples without the need for additional post-PCR manipulations

qPCR

Rapid and specific identification of T. canis and T. cati eggs in fecal and soil samples without the need for additional post-PCR manipulations

LAMP

A cheap, powerful and convenient approach for monitoring the contamination of soil with Toxocara eggs

  1. OT Ocular toxocariasis, CT Covert or common toxocariasis, ECP Eosinophil cationic protein, VLM Visceral larva migrans, TES-Ag Toxocara excretory secretory antigens