Bacillus sphenoides: A Promising Biocontrol Tool for Combating Japanese Encephalitis within a One Health Framework
1Mohamed Yahya*, 2Ankit Kumar
1BVSc & AH, Madras Veterinary College, Tamil Nadu Veterinary and Animal Science University, Chennai – 600007, Tamil Nadu
2Intern Student, Veterinary College & Research Institute Namakkal, TANUVAS
*Corresponding author – sciencegroup600@gmail.com
Abstract
Japanese encephalitis (JE) is a mosquito-borne zoonotic viral disease caused by the Japanese encephalitis virus (JEV). This study investigates the potential of Bacillus sphenoides B.42 for controlling Culex tritaeniorhynchus larvae, the primary vector of JE in India. The findings demonstrate the effectiveness of B. sphenoides B.42 in eliminating C. tritaeniorhynchus larvae in paper factory effluent (PFE) for up to 7 days post-application. However, the bacterium’s persistence beyond 91 days did not translate to continuous larval suppression, suggesting an inability to recycle within PFE.
Keywords
Japanese encephalitis, JEV, Culex tritaeniorhynchus, Bacillus sphenoides, biological control, mosquito larvae
Introduction
Japanese encephalitis (JE) is a mosquito-borne zoonotic viral disease caused by the Japanese encephalitis virus (JEV). The occurrence of disease is widespread in 24 countries of Southeast Asia and the Western Pacific region. The main vector of JE is Culex tritaeniorhynchus, prevalent across India. The primary preventive method for JE is vaccination; no specific treatment exists, but case management is advised based on symptoms. The disease primarily affects children but can infect individuals of any age.
Bacillus sphenoides is well-documented for its insecticidal properties against Culex spp. and some Anopheles spp. mosquito larvae in both laboratory and field trials [1, 2]. Studies have employed various B. sphenoides formulations to demonstrate its efficacy as a biocontrol agent and its potential for recycling within larval habitats or cadavers [3-5, 12]. However, treatment with sporulated B. sphenoides preparations doesn’t lead to epizootic outbreaks in subsequent larval populations. This study investigates a streptomycin-resistant strain of B. sphenoides B.42 and its effectiveness in controlling Culex tritaeniorhynchus larvae breeding in PFE.
Effect of Japanese encephalitis in Humans
Common symptoms of JE include headache, fever, mental confusion, and delirium. Acute encephalitis syndrome (AES) is the clinical presentation of the disease, characterized by symptoms such as convulsions, altered sensorium, and changes in behavioral patterns.
Most human infections have limited or no signs of illness. When clinical signs are present, they often have a rapid onset with high fever, headache, and neck stiffness. Brain infection (encephalitis) can cause disorientation, tremors or convulsions (especially in infants), paralysis, and coma. Infections are generally more severe in infants and the elderly.
Effect of Japanese encephalitis in Animals
Horses typically show no signs of disease. Rare cases may develop brain infection (encephalitis), presenting with fever, difficulty walking, stupor (trance), and teeth grinding. Signs typically appear 8 to 10 days after exposure to the virus. In pigs, reproductive problems like stillbirths, abortions, mummies, and infertility may occur. Piglets born alive often exhibit tremors and convulsions. The incubation period in pigs is uncertain. Many infected animals, such as cattle, dogs, cats, and birds, show no signs of illness.
Transmission
JEV is an arthropod-borne virus (arbovirus) transmitted in an enzootic cycle among mosquito vectors and vertebrate hosts, particularly pigs and birds. Humans become infected through the bite of an infected mosquito (Fig. 2) [43, 44]. While many vertebrate animals can be infected with JEV, domestic pigs are the major amplifying host for virus transmission to humans. This is because pigs develop high titers and long-lasting viremia after natural infection and live in close proximity to human settlements [45]. Ardeid birds are another important amplifying host, potentially contributing to the long-distance spread of JEV into new geographic locations since the virus causes no clinical signs in these natural hosts [46]. Various mosquito species can participate in the enzootic cycle, but culicine mosquitoes (primarily Culex tritaeniorhynchus) are the principal vectors for human infection [45, 46]. Humans, horses, and other non-avian vertebrates are considered incidental dead-end hosts because they do not produce a high enough level of viremia to infect new mosquitoes [15, 17]. In addition to horizontal transmission via mosquitoes, JEV can also be transmitted vertically from infected mosquitoes to their progeny through eggs.
Bacillus sphenoides and pathogenesis in Culex tritaeniorhynchus Mosquito
Bacillus sphenoides is a Gram-positive, spore-forming bacterium with insecticidal properties against mosquito larvae, particularly Culex species. The larvicidal activity of B. sphenoides is attributed to a combination of factors, including the production of crystal toxins and disruption of the larval gut.
The crystal toxins produced by Bacillus sphenoides are specifically toxic to mosquito larvae. Ingestion of these toxins by the larvae leads to a series of events that ultimately cause death. The toxins bind to specific receptors in the larval midgut, causing pores to form in the gut membrane. This disrupts the midgut barrier, leading to electrolyte imbalance and cell lysis (rupture). Additionally, B. sphenoides may contribute to the larvicidal effect by producing digestive enzymes that break down the larval gut tissues.
Conclusion
This study demonstrates the potential of Bacillus sphenoides B.42 as a biocontrol agent for Culex tritaeniorhynchus larvae in paper factory effluent. The effectiveness in eliminating larvae for up to 7 days post-application offers a promising approach for mosquito control. However, the inability of the bacterium to recycle within PFE beyond its persistence period necessitates further investigation into alternative application strategies or formulation improvements to enhance its long-term efficacy in such environments. Future research could also explore the potential for combining B. sphenoides with other mosquito control methods for a more comprehensive approach to managing Culex tritaeniorhynchus populations and reducing the risk of JE transmission.
References
- The Center for Food Security and Public Health- https://www.cfsph.iastate.edu ›
- Japanese Encephalitis – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4185882/
- Davidson, E.W., Sweeney, A.W. and Cooper, R. (1981) Comparative field trials of BaciNuF sphaericw strain 1593 and B. thuringiensis var. ismelensis commercial powder formulations. J. Econ. Entomol. 74, 350-354.
- Centers for Disease Control and Prevention. (2022, April 13). Japanese encephalitis (JE). Centers for Disease Control and Prevention.
- https://www.cdc.gov/japanese-encephalitis/index.html
