Read the paragraph from The Hot Zone. She took up a scalpel and slit the monkey's abdomen, making a slow and gentle cut, keeping the blade well away from her gloved fingers. The spleen was puffed up and tough, leathery, like a globe of smoked salami. She did not see any bloody lesions inside this monkey. She had expected that the monkey's interior would be a lake of blood, but no, this monkey looked all right, it had not bled into itself. If the animal had died of Ebola, this was not a clear case. She opened up the intestine. There was no blood inside it. The gut looked okay. Then she examined the stomach. There she found a ring of bleeding spots at the junction between the stomach and the small intestine. This could be a sign of Ebola, but it was not a clear sign. It could also be a sign of simian fever, not Ebola. Therefore, she could not confirm the presence of Ebola virus in this animal based on a visual inspection of the internal organs during necropsy. Which statement best summarizes the central idea of this paragraph?