Prevalence of Leptospira interrogans in wild rats (Rattus norvegicus and Cricetomys gambianus) in Zaria, Nigeria

Risk practices and awareness of leptospirosis amongst residents of Zaria, Nigeria

This study evaluated the level of risk practices and awareness of leptospirosis among residents of Zaria, Nigeria. A pre-tested questionnaires were administered via face-to-face interview to 100 residents. The data was analyzed using chi-square and multivariate analysis to identify risk factors for leptospirosis. The demography showed that the majority of the respondents were male, aged 21-40 years, and majorly crop farmers. The risk factors identified showed that males were 4.14 times more likely to be affected by leptospirosis (OR 4.14, 95% CI [1.93-5.37], p = 0.02) and the source of animal's water was 5.56 times more likely to be contaminated by Leptospira spp. (OR 4.14, 95% CI [2.88-8.03], p = 0.01) and these relationships were significant. The majority of respondents were not aware of the disease (OR 1.87, 95% CI [1.22-4.57], p = 0.01) with 78% of the respondents not sure of which of the animal species leptospirosis affected (OR 1.67, 95% CI [1.07-2.62], p = 0.02). This study has demonstrated the existence of risk behaviors, and paucity of knowledge about leptospirosis in the study area. It is therefore recommended to organize an enlightenment program and the need for protective clothing for individuals occupationally at risk of infection by Leptospira spp.

A strategy to improve rodent control while reducing rodenticide release into the environment

In addition to having a negative impact on the health of people and domestic animals, rodents often cause enormous damage to the environment by disrupting natural biodiversity. The negative impacts of rodents in urban and rural areas have required intensive use of rodentcides in spite of the proven risk of secondary poisoning of non-target predators and scavengers. Continuous and intensive use of rodenticides has led to environmental pollution through their retention in the environment. Commensal rodents are predominantly managed with anticoagulant rodenticides, which are very persistent in the environment and move up the food chain and accumulate in the bodies of predators and scavengers. Generally, the use of anticoagulant rodenticides continues, and there is a need to take appropriate measures to reduce their harmful impact. The efficacy of second generation anticoagulants (bromadiolone, difenacoum and brodifacoum), combined either mutually or with chlorophacinone at reduced doses (0.001 % and 0.0008 %), in controlling brown rats (Rattus norvegicus) was tested in a four-day no-choice feeding test. Combinations of second generation anticoagulants were more effective than the combination of chlorophacinone and second generation anticoagulants. The results indicate that combinations of different anticoagulants at multifold lower doses than the standard may provide a successful tool for brown rat control and a more environment-friendly method of rodent control and protection of non-target animals.

Optimal control and cost-effectiveness analysis for leptospirosis epidemic

This paper aims to apply an optimal control theory for the autonomous model of the leptospirosis epidemic to examine the effect of four time-dependent control measures on the model dynamics with cost-effectiveness. Pontryagin's Maximum Principle was used to derive the optimality system associated with the optimal control problem. Numerical simulations of the optimality system were performed for different control strategies and the results were presented graphically with and without controls. The optimality system was simulated using the Forward-Backward Sweep method in the Matlab programme. The numerical results revealed that the combination of all optimal control measures is the most effective strategy for minimizing the spread and impact of disease in the community. Furthermore, a cost-effectiveness analysis was performed to determine the most cost-effective strategy using the incremental cost-effectiveness ratio approach and we observed that the rodenticide control-only strategy is most effective to combat the spread of disease when available resources are limited.

A Mathematical Model Analysis for the Transmission Dynamics of Leptospirosis Disease in Human and Rodent Populations

This work is aimed at formulating and analyzing a compartmental mathematical model to investigate the impact of rodent-born leptospirosis on the human population by considering a load of pathogenic agents of the disease in an environment and the incidence rate of human infection due to the interaction between infected rodents and the environment. Firstly, the basic properties of the model, the equilibria points, and their stability analysis are studied. We also found the basic reproduction number (R₀) of the model using the next-generation matrix approach. From the stability analysis, we obtained that the disease-free equilibrium (DFE) is globally asymptotically stable if R₀ < 1 and unstable otherwise. The local stability of endemic equilibrium is performed using the phenomenon of the center manifold theory, and the model exhibits forward bifurcation. The most sensitive parameters on the model outcome are also identified using the normalized forward sensitivity index. Finally, numerical simulations of the model are performed to show the stability behavior of endemic equilibrium and the varying effect of the human transmission rates, human recovery rate, and the mortality rate rodents on the model dynamics. The model is simulated using the forward fourth-order Runge-Kutta method, and the results are presented graphically. From graphical stability analysis, we observed that all trajectories of the model solutions evolve towards the unique endemic equilibrium over time when R₀ > 1. Our numerical results revealed that decreasing the transmission rates and increasing the rate of recovery and reduction of the rodent population using appropriate intervention mechanisms have a significant role in reducing the spread of disease infection in the population.

Molecular detection and characterization of pathogenic Leptospira species in bats (Chiroptera) roosting in human habitats in Nigeria, West Africa

Leptospirosis is a neglected zoonosis with a nearly global distribution. In order to determine the role of bats in the epidemiology of leptospirosis in Nigeria, a total of 231 bats belonging to three families, Pteropodidae (n = 117), Molossidae (n = 107) and Nycteridae (n = 17), roosting in human habitats were screened by PCR and sequencing for the detection of pathogenic Leptospira species. DNA extracted from the kidneys of bats were subjected to conventional PCR targeting the rrs1, rrs2, flaB and secY genes for the detection of pathogenic Leptospira spp. Overall, 27 out of the 231 (11.7%) of the samples screened were positive for Leptospira spp. High prevalence (>80%) of Leptospira spp. DNA was detected in Chaerophon and Nycteris bat species captures in an abandoned well located within a human habitation. Sequences generated in this study were highly identical to Leptospira borgpetersenii and Leptospira interrogans and clustered with sequences of pathogenic species in GenBank. The detection of pathogenic Leptospira spp. was significantly associated (p < .001) with the bat species, feeding habit, roosting site and study location. To the best of our knowledge, this is the first molecular detection and characterization of pathogenic Leptospira spp. in bats from Nigeria. Results show that bats in Nigeria are infected with diverse Leptospira genotypes phylogenetically related to known pathogenic, including zoonotic taxa. Together, these findings reinforce bats' roles as potential reservoirs of Leptospira spp. and should be considered as a starting point for future comparative studies to improve our understanding of the epidemiology of this bacterial pathogen in Nigeria.