Novel astroviruses in insectivorous bats

Abstract

Bats are increasingly recognized to harbor a wide range of viruses, and in most instances these viruses appear to establish long-term persistence in these animals. They are the reservoir of a number of human zoonotic diseases including Nipah, Ebola, and severe acute respiratory syndrome. We report the identification of novel groups of astroviruses in apparently healthy insectivorous bats found in Hong Kong, in particular, bats belonging to the genera Miniopterus and Myotis. Astroviruses are important causes of diarrhea in many animal species, including humans. Many of the bat astroviruses form distinct phylogenetic clusters in the genus Mamastrovirus within the family Astroviridae. Virus detection rates of 36% to 100% and 50% to 70% were found in Miniopterus magnater and Miniopterus pusillus bats, respectively, captured within a single bat habitat during four consecutive visits spanning 1 year. There was high genetic diversity of viruses in bats found within this single habitat. Some bat astroviruses may be phylogenetically related to human astroviruses, and further studies with a wider range of bat species in different geographic locations are warranted. These findings are likely to provide new insights into the ecology and evolution of astroviruses and reinforce the role of bats as a reservoir of viruses with potential to pose a zoonotic threat to human health.

FIG. 1.

Schematic diagrams of the mink astrovirus (MAstV) genome and bat astrovirus (BatAstV) AFCD337 partial genome. ORFs, protease motif (Pro), and RdRp motif are shown in the diagram. The unsequenced putative 5′ end of the genome region of BatAstV AFCD337 is represented by a dotted line. The 2.5-kb ORF1a (partial) region and the ORF1b and ORF2 regions used for phylogenetic analysis in Fig. 2 are indicated by arrows. A_n, poly(A) tail.

FIG. 2.

Phylogenetic analysis of the partial ORF1a (∼800 nt), ORF1b, and ORF2 nucleotide sequences comparing bat astrovirus AFCD337 (underlined) with astroviruses of other species. Nine other bat astrovirus sequences are included in the ORF1a (partial) and ORF1b phylogenetic trees. Alignment was based on the encoded amino acid sequences. Astroviruses are indicated as follows: BatAstV, bat; MAstV, mink; OAstV, ovine; HAstV-1, human type 1 (also types 4, 5, and 8); and TAstV-1, turkey type 1.

FIG. 3.

Phylogenetic tree constructed with RdRp gene sequences (422 nt) amplified by an RT-PCR screening assay. Sequences of 77 bat astroviruses (BatAstVs) and other respective sequences of different astroviruses isolated from human (HAstV types 1, 2, 4, 5, and 8), mink (MAstV), ovine (OAstV), and turkey type 1 (TAstV-1) viruses were included and aligned based on the nucleotide sequences. For the bat specimens collected during the phase 2 longitudinal study, the sampling dates are indicated in parentheses on the right according to the following code: 1, June 2005; 2, August 2005; 3, December 2005; 4, March 2006.

FIG. 4.

Phylogenetic tree constructed with 750-nt sequences of the RdRp gene and ORF1b (3′ end) of representative astroviruses isolated from bat (BatAstV), human (HAstV types 1, 4, 5, and 8), mink (MAstV), ovine (OAstV), and turkey type 1 (TAstV-1) viruses. These sequences were aligned based on the encoded amino acid sequences and were reverse-translated back to nucleotides for the phylogenetic analysis.