Development and evaluation of an indirect ELISA test for serodiagnosis of Linguatula serrata infection in sheep

Linguatula serrata as a cosmopolitan parasite is one of the parasitic zoonoses. The adult parasites live in the nasal airways or frontal sinuses of canids as the definitive hosts and larval stages in the liver¸ lung and mesenteric lymph nodes of ruminants as intermediate hosts. Humans may be infected by eating eggs or nymphs of the parasite. All intermediate hosts may be infected without showing any clinical signs. No serological methods presented for detection of the infection in herbivorous animals. In this study، for the first time، an indirect ELISA test was developed for the detection of Linguatula serrata infection in sheep by using somatic and excretory-secretory antigens، isolated from nymphs of the parasite. Nymphs of the parasite were collected from mesenteric lymph nodes of infected sheep and used for preparation of somatic antigens by sonication (250 nymphs/10ml، PBS- RPMI1640). The excretory-secretory antigens were prepared by incubation of the larvae (200 nymphs/10ml) in RPMI-1640 media for 24 h. Appropriate dilutions of sera، anti-Sheep IgG conjugate، somatic and excretory-secretory antigens were determined as 1:100، 1:5000، 1:40 and 1:4 respectively. Evaluation of the ELISA was performed by 121 sera (73 positive and 48 negative). The sensitivity، specificity، positive predictive value (PPV)، negative predictive value (NPV) and accuracy of the ELISA for somatic antigen were 90. 4%، 75. 0%، 84. 6%، 83. 7%، 84. 2% and those for excretory-secretory antigen were 89. 0%، 93. 8%، 95. 6%، 84. 9% and 90. 9%، respectively. Data analysis of the present study by SPSS software and Mac Nemar Test showed that excretory-secretory antigens are better than somatic antigens for detecting of the infection in sheep. Therefore the ELISA test using excretory-secretory antigen of nymphs of Linguatula serrata can be used for detection of infection in sheep، especially in epidemiologic studies and developed for other hosts.