They are most likely infected through the natural reservior as humans. The Ebola virus can be transmitted via contact with blood, secretions, organs, or semen of infected patients. The disease is very easily spread from person to person through close physical contact. This is very common in situations where the infected person is being cared for by family members or hospital workers. The virus has also been transmitted through reused needles during treatment of patients.
Sexual contact can also spread the virus.
Contact with an infected person who shows no symptoms is highly unlikely to result in spreading the disease. Such asymptomatic cases have been documented, with patients having both IgM and IgG responses to Ebola antigens. The lack of symptoms is most likely associated with the immune response. This asymptomatic infection could have an affect on future treatments. For more information, see Ebola 2000 paper analysis .