EVALUATION OF THREE METHODS FOR ROUTINE DIAGNOSIS OF LEPTOSPIROSIS IN NIGERIA

Abstract

In Nigeria, the occurrence of leptospirosis, a zoonotic disease is not well known and is often suspected based on clinical signs, many of which are common to some febrile conditions such as babesiosis, malaria, typhoid fever and influenza. Due to poor availability of relevant laboratory facilities, the confirmation is always based on post mortem histology. Early and rapid diagnosis as well as update of information on occurrence of the disease, are essential for prevention, surveillance, good prognosis and control. Many techniques that combine sensitivity, rapidity and cost-revenue ratio assessment are not routinely used in Nigeria. However, many techniques are available in developed countries. Assessment of the morbidity and case fatality rates of leptospirosis in dogs and evaluation of three methods for use in Nigeria were carried out. A review of 5,250 cases of different ailments in dogs presenting in two referral veterinary hospitals in Ibadan between 2005 and 2010 was carried out to assess the occurrence of leptospirosis. In addition, an evaluation of the relative sensitivity, specificity, accuracy (according to standard formulae), rapidity and cost per unit test of Dark Field Microscopy (DFM) using hyper-spectral imaging, Fluorescent Antibody Staining (FAS) and conventional Polymerase Chain Reaction (PCR) was carried out using 90 urine samples from cattle and 16, 30, 5, 2, 7, 2, 10 and 5 kidney samples from cattle, dogs, bob cats, beavers, raccoons, coyotes, foxes and opossums respectively. The rapidity was calculated as the unit time taken for each technique. The operating cost per annum and the cost per unit test for each technique were calculated using standard methods. Data of the reviewed cases and agreement of the techniques were analysed using descriptive and Kappa statistics respectively. Leptospirosis morbidity and case fatality rates in dogs were 47.0%, and 37% respectively. The relative sensitivity, specificity and accuracy of DFM compared with FAS were 88.0%, 96.0%, 94.7%, respectively and compared with PCR were 64.7%, 73.5%, 72.5% respectively. The relative sensitivity, specificity and accuracy of PCR compared with FAS were 34.3%, 99%, 83.2% respectively. The Kappa statistics showed perfect agreement (k=0.99) between DFM and FAS, DFM and PCR and between PCR and FAS. Rapidity of the tests were 26.1 minutes, 120.0 minutes and 305.0 minutes per test for DFM, FAS and PCR respectively. The cost per unit test for DFM, FAS and PCR were ₦744, ₦1,975 and ₦7,014 respectively. Leptospirosis morbidity and case fatality rates in dogs in this study were high and this poses a great health challenge. The Dark Field Microscopy using hyperspectral imaging technique which was the fastest and cheapest per unit test may be of benefit for routine use in Nigeria to improve diagnosis and subsequently reduce mortality.

Key words: Leptospirosis, Morbidity rate, Diagnostic technique, Accuracy, Cost