Research Article: Bat rabies in Washington State: Temporal-spatial trends and risk factors for zoonotic transmission (2000–2017)

Date Published: October 9, 2018

Publisher: Public Library of Science

Author(s): Jesse Bonwitt, Hanna Oltean, Misty Lang, Rochelle M. Kelly, Marcia Goldoft, Charles E Rupprecht.


Rabies is a zoonotic viral disease that can affect all mammals. In the United States, the majority of human rabies cases are caused by bats, which are the only known reservoirs for rabies virus (RABV) in Washington State. We sought to characterize bat RABV epidemiology in Washington among bats submitted by the public for RABV testing.

We examined temporal and spatial trends in RABV positivity (% positive) for taxonomically identified bats submitted to diagnostic laboratories during 2006–2017. For a subset of Myotis species, we evaluated sensitivity and predictive value positive (PPV) of morphological identification keys, using mitochondrial markers (cytochrome b) as a reference. For bats tested during 2000–2016, we analyzed RABV positivity by circumstances of encounters with humans, cats, and dogs.

During 2006–2017, RABV positivity for all bat species was 6.0% (176/2,928). Among species with ≥100 submissions, RABV positivity was 2.0%–11.7% and highest among big brown bats (Eptesicus fuscus). An increasing trend in annual positivity was significant only for big brown bats (P = 0.02), and was circumstantially linked to a geographic cluster. Sensitivity and PPV of morphological identification keys was high for M. evotis but varied for M. lucifugus, M. californicus, M. yumanensis, and M. septentrionalis. A positive RABV result was significantly associated with nonsynanthropic species, abnormal behavior, abnormal hiding, injury, biting, found in a body of water, found alive, found outdoors, and caught by a dog.

Monitoring passive RABV surveillance trends enables public health authorities to perform more accurate risk assessments. Differences in temporal and spatial trends in RABV positivity by bat species indicate the importance of collecting taxonomic data, although morphological identification can be unreliable for certain Myotis species. Current public health practices for RABV exposures should be maintained as RABV infection in bats can never be excluded without diagnostic testing.

Partial Text

Rabies is a zoonotic viral disease caused by viruses of the genus Lyssavirus. All mammals are susceptible to infection, and disease is nearly always fatal after clinical onset. Of the more than 16 known Lyssavirus species, rabies virus (RABV) is the only one naturally present in the Americas [1, 2]. Bats and wild mesocarnivores constitute major reservoir species [3]. The majority of domestically acquired human rabies cases in the United States are caused by bats. During 2003–2017, 17 of 20 reported primary human rabies cases were associated with bat exposures or bat RABV variants [4, 5].

Analysis of passive bat RABV surveillance in Washington indicates that big brown bats are a major reservoir, and circumstantial evidence suggests the possible presence of an epizootic during 2016–2017 west of the Cascade Range. Whereas certain species, ecological characteristics (nonsynanthropic species), seasons, and circumstances of encounters present a heightened risk of bat RABV infection, none of these variables can conclusively exclude bat RABV infection. Contact with bats should therefore always warrant a public health evaluation and current public health practices for RABV exposures in humans, cats, and dogs, should be maintained.




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