ABSTRACT
The rabies virus causes an acute encephalomyelitis that is fatal in 100% of cases. Most mammals are susceptibile to this virus. Bats (Chiroptera), however are able to withstand infections and are well known reservoirs of this virus. Bats appear to have developed an immune mechanism that fights the severity of the infection. The present study was designed to investigate the neuropathogenesis of experimental infection with the rabies virus (RABV) in African Straw Coloured Fruit Bats (Eidolon Helvum). The study examined the effect of the infection on the neurons of the cerebral cortex, cerebellar cortex and hippocampus as well as morphology and haematological parameters of the bats and the innate immune response using in situ reverse transcription polymerase chain reaction (RT PCR) to detect cytokine (TNFα, IFNα, IFNλ, IL2 and IL4) expression levels. Forty African Straw Coloured Fruit bats were obtained from roosts around Samaru, Zaria. Thirty five bats were experimentally infected with 105 median mouse intracerebral lethal dose (MICLD50) of the rabies virus intramusculary into both left and right masseter muscles and then randomly grouped into seven groups (n= 5). One group served as control which were sham inoculated with 0.02mls of distilled water. One group was sacrificed on each day 1, 3, 5, 7, 14, 21 and 28 days post inoculation (pi). Blood and brain tissue were collected at time of sacrifice for haematological and histological analysis and RT PCR. Physical observations revealed no clinical symptoms in the bats throughout the period of experiment. Rabies glycoprotein and nucleoprotein mRNA were expressed at day 7 pi with rabies nucleoprotein exhibiting a higher levels of expression. The haematological investigation revealed significant increases in haemoglobin (Hb) concentration, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC) and neutrophils, while decreases were observed in lymphocytes and no significant difference were seen in packed cell volume (PCV), platelet, eosinophil and basophil counts at p<0.05. Significant increases in expression levels of IL2, IFNα and IFNλ were recorded (p<0.05). There was no significant increases in TNFα expression levels at p<0.05). Histological analysis revealed neuronal vacoulation, pyknosis and necrosis as well as degenerated cells and gliosis in the experimental groups. In conclusion, experimental infection of the African Straw Coloured Fruit Bats (Eidolon Helvum) with rabies was achieved and that the animals were able to survive the infection and significant increase in neutrophils was observed (p<0.05). The specific cytokines involved in the innate immune response were determined and significant increases in cytokine levels were observed in IL2, IFNα and IFNλ (p<0.05).