A preliminary assessment of the recombinant antigen PLA2 in the diagnosis of human dirofilariosis

Development of New Recombinant DgK Antigen for Diagnosis of Dirofilaria immitis Infections in Dogs Using ELISA Technique and Its Comparison to Molecular Methods

Background

Dirofilaria immitis is a cosmopolitan zoonotic, vector-borne parasite of carnivorous animals causing dirofilariasis in human beings. Common commercial serodiagnostic tests for canine dirofilariasis usually lead to different results in their sensitivity and specificity. The present study reports development of recombinant DgK (rDgK) antigen of D. immitis for accurate immunodiagnosis of D. Immitis-infected dogs using indirect ELISA test.

Methods

The rDgK coding sequence was successfully sequenced, codon optimized and cloned into pET-24a(+) expression vector and then expressed in Escherichia coli. The recombinant DgK was affinity purified using Ni²+-charged HiTrap chelating column, followed by testing in Western blotting and enzyme-linked immunosorbent assays (ELISA) with dog sera from a dirofilariasis endemic area. The performance of rDgK ELISA was evaluated using 60 sera collected from suspected dogs, while molecular technique was used as a reference test.

Results

Sera from positive control D. immitis infection produced a strong IgG antibody response to rDgK both in ELISA and Western blotting tests. The sensitivity and specificity related to diagnostic potential of rDgK for ELISA were 92.5% and 87.5%, respectively. The results of rDgK ELISA showed a high agreement (0.764) with molecular identification.

Conclusion

The findings revealed that the developed new rDgK antigen is sensitive and specific for immunodiagnosis of canine dirofilariasis using ELISA test.

Diagnosis of human filariases (except onchocerciasis)

The traditional method of diagnosing filarial infections is to examine blood or skin samples for microfilariae and for many this is still the standard procedure. However, since the present global campaign to eliminate lymphatic filariasis new diagnostic tools have emerged like PCR, antigen detection using finger-prick blood taken during the day and ultrasound to visualize adult worms. The last two can be applied in endemic countries with limited resources and enable the detection of early infections. As well as their value in control schemes, the latter is particularly important for the individual since recent research has shown that damage is usually caused long before symptoms appear. The usefulness in different situations and the advantages and disadvantages of the various new tools for diagnosis of lymphatic filariasis are discussed. For loiasis, immunodiagnostic methods have not been very successful but repetitive DNA sequences in the Loa genome have been found to be species specific. Techniques based on them are particularly useful for diagnosing cases of occult infection without microfilaraemia. There have been no advances in the diagnosis of Mansonella perstans but both immunodiagnostic and PCR tests show promise in differentiating M. streptocerca, and the latter in differentiating M.ozzardi, from Onchocerca. In addition to the human filariae, the dog parasites Dirofilaria immitis and D. repens can also occur in humans but do not produce microfilariae in them. ELISAs and PCR probes have been devised and can usefully differentiate between pulmonary dirofilariasis and lung cancer.

Human dirofilariasis in the European Union

The dog parasites Dirofilaria immitis and D. (Nochtiella) repens, well known as zoonotic agents, are widely distributed in southern Europe. Although both species are canine parasites, infection with immature worms has been found in humans, who develop nodules, mainly in subcutaneous tissue or in lung parenchyma arising from branches of the pulmonary artery. In humans, the parasites do not usually reach the adult stage and microfilaremia is absent, as has been shown by diagnosis using invasive methods for removing the nodules. In this article, Antonio Muro, Claudio Genchi, Miguel Cordero and Fernando Simón review the current situation concerning the clinical and epidemiological aspects, immune response and diagnosis of human dirofilariases.