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Black rats rainforest invasion 'speeded by deforestation' By Matt McGrath   Cutting down trees in rainforests facilitates the spread of invasive black rats, a study suggests. The rodents normally avoid mature forests with large trees as they provide little in the way of cover. But researchers, writing in Biotropica, say that logging makes rainforests more attractive for rats as fallen wood contains more insects which they eat. Scientists are concerned that the invading black rats will be bad news for native mammals. Sometimes called the ship rat, these rodents have spread around the world over the past 400 years, often causing the extinctions of native species and spreading disease. Noisy trails Much of their notoriety rests on the idea that black rats were the origin of bubonic plague, although recent research casts doubt on that notion. Black rats have usually avoided older forests as they contain large trees which do not provide much in the way of ground level protection. They also tend to have leafy forest floors which are noisy for rats to run through, as they attract predators. This new study examined the idea that logging of trees in rainforests might facilitate the spread of the rodents. The researchers looked at the island of Borneo where large tracts of the natural forest have been degraded. It had been believed that black rats were confined to urban areas in Borneo. To test the idea that they might spread into deforested regions, the scientists trapped rats from four different species - they then attached small spools of cotton thread to their backs and and tracked their movements. Across the animals in the study, the researchers found that the black rats had the strongest preference for the type of disturbed habitat associated with logging. The increased amount of fallen wood boosted the amount of insects which the rats eat. The logged forests also have more undergrowth which provides better cover. The researchers believe that black rats favour these small changes far more than related species. "Logging creates micro-environments that black rats love, helping them move in," said study co-author Dr Rob Ewers from Imperial College London. "This could be bad news for native mammals who might not be able to compete with black rats for food and resources. It's also bad for the forest, as many small mammals are important seed dispersers, helping rainforest plants to grow, and they are also prey for larger animals." The researchers say that the widespread destruction of forests throughout the tropics may well be multiplying the threat from invasive species like black rats. They believe the presence of these rats could pose a significant threat to nesting birds and other small mammals. The scientists say that the way that logging is done can have a big impact on the suitability of the land for the black rats. The more dead wood that is left behind the better the black rats like it. If felled trees were more accurately cleared as well as the vines that connect the trees, the rat's progress might be curbed.

Spread of disease from Rats mapped
Scientists say they have developed a better way to predict how animal diseases can spill over into humans. Their model for Lassa fever, which is spread by rats, predicts that there will be twice as many human cases of the disease in Africa by 2070. The method can be applied to other disease threats such as Ebola and Zika, they say. Like the Ebola virus, the Lassa virus causes haemorrhagic fever and can be fatal. Lassa fever virus currently affects between 100,000 and one million people a year in western sub-Saharan Africa. A rat found in parts of the continent can pass the virus to people. Scientists led by Prof Kate Jones of the Centre for Biodiversity and Environment Research at UCL looked at about 400 known outbreaks of Lassa fever between 1967 and 2012. Lassa fever Lassa virus is carried by the Mastomys rat, which is found in parts of Africa. The virus is passed to people through direct contact with infected rats by catching and preparing them for food, or by food or household items contaminated with rat droppings or urine. The virus can also be transmitted through contact with body fluids of an infected person. Around 80% of people with Lassa virus have no symptoms or have symptoms that mimic other illnesses, such as malaria. Symptoms include fever, fatigue, nausea, vomiting, diarrhoea, headaches, abdominal pains, sore throat and facial swelling.   They developed a model to calculate how often people are likely to come into contact with disease-carrying animals and the risk of the virus spilling over. It shows more areas of West Africa are at risk from Lassa fever spill-over events than previously thought. Disease outbreaks "Our model suggests that in future, it is likely to become a greater burden on local communities spreading to more areas with approximately twice as many spill-over events predicted by 2070," Dr Jones and colleagues from the University of Cambridge and the Zoological Society London report in the journal, Methods in Ecolspreadogy and Evolution. The method takes into account environmental change and the way human populations are expected to grow. The projected increase in cases is largely due to climate change, with the rat that passes it to people (M. natalensis) thriving in hot and wet conditions, they say. Meanwhile, growth in human populations in certain areas will mean more people coming into contact with the rodent. "This model is a major improvement in our understanding of the spread of diseases from animals to people," explained Prof Jones.   "We hope it can be used to help communities prepare and respond to disease outbreaks, as well as to make decisions about environmental change factors that may be within their control." Investment need More than 60% of emerging infectious diseases originate in animals. As well as well-known threats such as Ebola and Zika, other diseases including Lassa fever already affect thousands of people and are expected to spread as the world warms. "Our new approach successfully predicts outbreaks of individual diseases by pairing the changes in the host's distribution as the environment changes with the mechanics of how that disease spreads from animals to people, which hasn't been done before, " said co-researcher Dr David Redding of UCL. The researchers say the model can be refined to include diseases such as Ebola and Zika. Prof Jonathan Ball of the University of Nottingham, who was not involved in the research, said if the models hold true, then future climate change and population growth will significantly increase the number of Lassa fever outbreaks - and this is likely to be true for other infectious diseases. "The threat of emerging and neglected diseases will not go away and we need to invest in research and global healthcare systems to ensure that we are ready to deal with these threats and their consequences," he said. By Helen Briggs