Of rats and pathogens: pathogens transmitted by urban rats with an emphasis on hantaviruses.

Abstract Rats (brown- or Norway- and black: Rattus norvegicus and Rattus rattus, respectively) are very invasive rodents. They are originated from Southeast Asia and are present now everywhere in the world, exploiting their extraordinary capacity to proliferate in close contact with human populations. Rats, and particularly the brown rat, take advantage of conditions raised by overpopulation in cities, lack of hygiene and poverty. Beside the significant damage caused by their presence in rural and urban ecosystems, rats are also dangerous carriers of numerous pathogens transmissible to humans. Among these pathogens, leptospira and hantaviruses (particularly Seoul virus or SEOV) are the most important. Seoul virus belongs to the virus family Bunyaviridae and genus Hantavirus, has a worldwide distribution, and causes haemorrhagic fever with renal syndrome (HFRS) in humans. Leptospira and particularly Leptospira interrogans, serogroup Icterohaemorrhagiae, are zoonotic bacteria very frequently borne and excreted by rats and cause severe disease - leptospirosis - both in humans and domestic animals. Next-generation sequencing confirmed that rats can carry many other microbes and parasites for which the zoonotic capacity is not always determined. The importance of rats as pests and carriers of numerous pathogens demands the fight against their proliferation, especially in urban environments. The use of rodenticides such as anticoagulants is one pillar of prevention. However, increasing levels of rodenticide resistance can often render this means of control as ineffective. The second and absolutely necessary pillar of prevention involves the control of all environmental factors, which favour the establishment and proliferation of rats: age of housing, density of dwellings, defective drains/sewers, poor structural maintenance, proximity to food sources and poor hygiene.