Comparison of Rift Valley fever virus replication in North American livestock and wildlife cell lines

Abstract

Rift Valley fever virus (RVFV) causes disease outbreaks across Africa and the Arabian Peninsula, resulting in high morbidity and mortality among young domestic livestock, frequent abortions in pregnant animals, and potentially severe or fatal disease in humans. The possibility of RVFV spreading to the United States or other countries worldwide is of significant concern to animal and public health, livestock production, and trade. The mechanism for persistence of RVFV during inter-epidemic periods may be through mosquito transovarial transmission and/or by means of a wildlife reservoir. Field investigations in endemic areas and previous in vivo studies have demonstrated that RVFV can infect a wide range of animals, including indigenous wild ruminants of Africa. Yet no predominant wildlife reservoir has been identified, and gaps in our knowledge of RVFV permissive hosts still remain. In North America, domestic goats, sheep, and cattle are susceptible hosts for RVFV and several competent vectors exist. Wild ruminants such as deer might serve as a virus reservoir and given their abundance, wide distribution, and overlap with livestock farms and human populated areas could represent an important risk factor. The objective of this study was to assess a variety of cell lines derived from North American livestock and wildlife for susceptibility and permissiveness to RVFV. Results of this study suggest that RVFV could potentially replicate in native deer species such as white-tailed deer, and possibly a wide range of non-ruminant animals. This work serves to guide and support future animal model studies and risk model assessment regarding this high-consequence zoonotic pathogen.

Keywords: Rift Valley fever virus; livestock diseases; permissiveness; virus replication; wildlife reservoir.

FIGURE 1

Rift Valley fever virus (RVFV) replication kinetics in North American livestock and wildlife cell lines. Cell cultures derived from brain (A,B), kidney (C,D), and lung (E) were infected with MP-12 (A,C,E) or SA01-1322 (B,D) strains at 0.1 multiplicity of infection (MOI) and the viral titers were calculated by standard plaque assay at the indicated hours post infection (hpi). The mean of at least three biological replicates are represented with 95% confidence intervals.

FIGURE 2

Relative viral RNA levels in North American livestock and wildlife cell lines. Real time reverse transcription polymerase chain reaction (RT-PCR) was performed on time point samples from brain (A,B), kidney (C,D), and lung (E) cell lines infected with MP-12 (A,C,E) or SA01-1322 (B,D) strains. Expression of viral RNA was calculated relative to beta actin using the comparative Ct method. The mean of at least three biological replicates are represented with SEs.

FIGURE 3

Comparison of intracellular and extracellular virus in North American livestock and wildlife cell lines. Intracellular and extracellular virus titers (A,C) and relative viral RNA levels (B,D) are shown. The mean of at least three biological replicates are represented.