Which of the following is a vector that spreads viruses and bacteria?

Rats are known to be significant vectors for the transmission of various viruses and bacteria. They can carry and spread diseases such as hantavirus, leptospirosis, and salmonella, among others. Their close association with human habitats, as well as their high reproductive rate, make them particularly effective at transmitting pathogens.

In urban and rural settings, rats often thrive in environments where food and shelter are readily available, which enhances the likelihood of disease spread. They can contaminate food and water sources with their droppings and urine, leading to outbreaks of disease in human populations. This characteristic of rats as disease vectors is well-supported by scientific research and public health data, making them a primary concern in vector control efforts.

The other animals listed do not share the same widespread impact as vectors for humans, particularly in terms of common viral and bacterial diseases. While some may carry pathogens, their interaction with humans is much less frequent and impactful in public health terms.