bat-borne zoonoses: transmission, impact, prevention, and management

Global environmental drivers: anthropogenic climate change, deforestation, and biodiversity loss alter bat habitats and foraging patterns, driving frugivorous and insectivorous bats into urban and agricultural settings and increasing zoonotic spillover risks (1):

• exceptional host biology: bats serve as ideal viral reservoirs because they suppress pro-inflammatory immune responses—allowing them to maintain asymptomatic high-titer infections—and live in highly social colonies that facilitate rapid intra-species pathogen transmission
• key clinical pathogens: bat-associated pathogens of major public health significance include lyssaviruses (rabies virus, Australian bat lyssavirus), filoviruses (Ebola virus, Marburg virus), henipaviruses (Nipah virus, Hendra virus), and dimorphic fungi (Histoplasma capsulatum)

Pathogen-Specific Clinical Features and Transmission Pathways

1. Filoviruses (Ebola Virus and Marburg Virus)

• Ebola virus disease (EVD):
  • transmission: fruit bats (e.g., Hypsignathus monstrosus) and insectivorous bats are strongly suspected candidate reservoirs (supported by PCR RNA detection, seropositivity, and epidemiological links to bat handling/bushmeat), though direct isolation of live infectious virus from wild fruit bats remains unproven; secondary spread is driven by human-to-human contact with infectious body fluids (blood, sweat, vomitus, urine, stool, breast milk, and semen)
  • viral persistence: viable virus persists in immune-privileged sites (e.g., semen for >470 days post-recovery, leading to sexual transmission, and breast milk)
  • clinical presentation: incubation period 2 to 21 days (mean 6.2 days); high fever, severe myalgia, and fatigue, progressing to profuse gastrointestinal symptoms, shock, coagulopathy/haemorrhage, and multi-organ failure
  • mortality: pooled case fatality risk ranges from 53% to 75% depending on species (highest for Zaire ebolavirus)
• Marburg virus disease (MVD):
  • transmission: primary spillover from cave-roosting Egyptian fruit bats (Rousettus aegyptiacus); secondary spread occurs via direct contact with infectious body fluids
  • clinical presentation: incubation period 3 to 13 days; sudden onset of high fever, severe headache, watery diarrhoea, abdominal cramps, and severe haemorrhagic manifestations
  • mortality: pooled case fatality risk estimated at 61%

1. Lyssaviruses (Rabies Virus and Australian Bat Lyssavirus)

• rabies virus:
  • transmission: transmitted via saliva through bites, scratches, or mucous membrane contact; vampire bats (Desmodus rotundus) drive sylvatic transmission in the Americas, while dogs remain the main vector globally (>95% of human deaths)
  • clinical presentation: incubation period ranges from days to >1 year; progresses from non-specific paraesthesia and fever to furious rabies (hyperactivity, agitation, hydrophobia, aerophobia) or paralytic rabies (quadriplegia, bulbar palsy)
  • mortality: case fatality risk approaches 100% once clinical symptoms appear
• Australian bat lyssavirus (ABLV):
  • transmission: transmitted via scratches or bites from infected frugivorous (flying foxes) or insectivorous bats in Australia
  • clinical presentation: incubation period ranges from 3 weeks to 27 months; presents with fever, headache, and fatigue, rapidly escalating to severe encephalitis, muscle spasms, paralysis, and death
  • mortality: 100% case fatality risk (4 total recorded human cases)

1. Henipaviruses (Nipah Virus and Hendra Virus)

• Nipah virus (NiV):
  • transmission: direct contact with flying foxes (Pteropus spp.), ingestion of raw date palm sap contaminated with bat saliva/excreta (South Asia), contact with intermediate animal hosts (e.g., pigs in Malaysia, horses in the Philippines), or human-to-human contact
  • clinical presentation: incubation period 8 to 17 days; initial influenza-like illness escalating rapidly to acute encephalitis (confusion, seizures, cranial neuropathies) and severe respiratory distress
  • mortality & sequelae: pooled case fatality risk ranges from 28.9% (Malaysia) to 82.7% (India); 24% to 45% of survivors suffer long-term neurological or neuropsychiatric sequelae (cognitive impairment, chronic fatigue, relapsing encephalitis)
• Hendra virus (HeV):
  • transmission: spillover from Pteropus flying foxes to horses via urine/excreta-contaminated pasture or feed; transmitted to humans exclusively through close physical contact with infected horse body fluids
  • clinical presentation: incubation period 5 to 21 days; flu-like symptoms progressing to severe pneumonia and/or encephalitis
  • mortality: 57% case fatality risk (4 deaths out of 7 human cases)

1. Dimorphic Fungi (Histoplasma capsulatum)

• histoplasmosis:
  • transmission: inhalation of microconidia aerosolised from soil or organic matter heavily enriched with bat guano (e.g., caves, attics, hollow trees)
  • clinical presentation: incubation period 14 to 28 days; acute pulmonary disease (fever, dry cough, substernal chest pain), chronic cavitary lung disease, or progressive disseminated histoplasmosis involving multiple organ systems
  • mortality & risk groups: low mortality in immunocompetent individuals (~5%); high case fatality risk (20.8% to 52.8%) in individuals with advanced HIV/AIDS or severe immunosuppression

Prevention and Management Strategies

Immunisation and Post-Exposure Prophylaxis (PEP)

• Rabies & ABLV PEP:
  • Category I (touching/licking intact skin): wash exposed skin
  • Category II (minor scratches/nibbling without bleeding): immediate wound washing + rabies vaccine series (intradermal or intramuscular)
  • Category III (transdermal bites/scratches, bat exposure, saliva on mucous membranes): immediate thorough wound washing + rabies vaccine series + rabies immunoglobulin (RIG) infiltrated into/around the wound (RIG not required if previously vaccinated)
  • vaccine efficacy: intradermal (0.1 mL) and intramuscular (0.5/1.0 mL) routes demonstrate equivalent seroconversion rates ($\ge0.5\text{ IU/mL}$ by day 14)
• Ebola vaccination:
  • rVSV-AG-ZEBOV (Ervebo): FDA/EMA-approved single-dose live recombinant vaccine offering robust protection against Zaire ebolavirus in adults and children

Targeted Pharmacotherapy

• Zaire ebolavirus: FDA-approved monoclonal antibodies Inmazeb (REGN-EB3) and Ebanga (MAb114) significantly reduce day-28 mortality compared to standard care or older regimens
• histoplasmosis: liposomal amphotericin B is superior to deoxycholate amphotericin B for induction therapy in severe/disseminated disease; oral itraconazole is the drug of choice for consolidation and long-term suppression
• supportive care: mainstay of treatment for Marburg, Nipah, Hendra, Rabies, and ABLV (e.g., aggressive fluid/electrolyte management, seizure control, intensive care support)

One Health and Ecological Prevention

• barrier protection: physical exclusion of bats from living spaces, covering date palm sap collection pots with bamboo skirts, and avoiding cave/guano exposures
• animal health: routine vaccination of domestic dogs against rabies and horses against Hendra virus; keeping animal feed/water troughs covered away from bat roosts
• healthcare safety: strict barrier nursing, negative-pressure isolation, and dedicated personal protective equipment (PPE) during patient care

Reference:

1. Stanhope J, Boardman WSJ, Burrell C, Bi P, Weinstein P. Bat-borne zoonoses: transmission, impact, prevention, and management. BMJ. 2026;395:e100560. DOI: 10.1136/bmj-2026-100560.