internal sealed class Listener
{
    private readonly CancellationTokenSource cancellationTokenSource;

    public Listener()
    {
         this.cancellationTokenSource = new CancellationTokenSource();
    }

    public void Start()
    {
        Task.Factory.StartNew(LongRunningTask, cancellationTokenSource.Token);
    }

    private void LongRunningTask()
    {

        using(var connection = new... )
        using(var channel = connection.CreateChannel())
        {
             // EventingBasicConsumer is part of RMQ
             var consumer = new EventingBasicConsumer(channel);
             consumer.Received += Consumer_Received;

             while(!cancellationTokenSource.Token.IsCancellationRequested)
             {
                 // to avoid cpu hogging
                 Thread.Sleep(1);
             }
        }
    }

    private void Consumer_Received(object sender, BasicDeliveryArgs e)
    {
        OnMessageReceived(this, new MessageReceivedEventArgs()
        {
             // set some properties
        });
    }
}