Current Status of Large Animal Leptospirosis Based on Leptospira Research Laboratory Retrospective Study in Iran

Leptospirosis is a widespread zoonotic disease that is caused by spirochetes of the genus Leptospira. In Iran, flooding in some part of the country in 2019, caused more attention to disease distribution. Microscopic agglutination test is a gold standard for serological diagnosis of leptospirosis which is used in many reference laboratories.

During 2010 and 2020, a total of 4900 blood samples from cows, buffaloes, horses, sheep and camels were delivered to the Leptospira Research Laboratory for serological diagnosis. These samples came from different provinces of Iran for research purposes. The aim of this study was to determine the Current status of large animal Leptospirosis based on Leptospira Research Laboratory Findings in Iran using microscopic agglutination test.

All serum samples were tested using Microscopic Agglutination Test (MAT). The MAT method was conducted as described by WHO, 2003 with some modifications. Serum samples were tested by MAT using five live L. interrogans serotypes, Gripptyphosa, Icterohaemorrhagiae, Hardjo, Canicola, and Pomona. Three standard controls were included in the test; one positive standard serum, one negative standard serum. Ten μL of the appropriate antigen was added to 10 μL of each diluted serum sample on a microscope slide. The microscope slide was placed in a petri-dish with moist paper to avoid evaporation, and incubated at 29C for 90 minutes. The slide was examined under dark-field microscope (Olympus BX50), using a long working distance objective at x100 or x200 magnification. Agglutination was noted by observing clumps of leptospires. If more than 75% of the leptospira were agglutinated, the sample was considered positive at 1.100 dilution. Finally, the highest titre in which ≤75% agglutination was occurred was recorded as the final titre of antibody in the serum sample.

The results of this study showed that the rate of seropositive in buffaloes 44%, cows 1.2-33.5%, horses of Guilan 31.6%, sheep 8.3-15% and in camels it was 2%. However. The highest rate of infection was in northern part of Iran, whereas the lowest rate of infection was seen in dried area. It was also noted that the rate of infection during the Covid-19 pandemic seems to be reduced in compare to the year before.

The results of this study showed that there is a close coloration between climate change, farm hygienic score the rate of seropositive cases. It seems that the emphasis on compliance with health protocols and disinfection by health authorities during the Covid-19 pandemic, has some effects on reducing the rate of infectious diseases as we have seen in current study. However, further epidemiological studies are needed to prove this theory.