Parasitic diseases are not considered as contagious diseases. As such, it is usually not possible to catch a parasitic disease just by being in the same room with an infected person, like it is the case for some common viral infections, such as cold, flu or gastroenteritis. In fact, it means that being in contact with secretions from an infected person does not usually transmit parasitic diseases. It also implies that parasites rarely caused massive epidemics, unlike some common viruses, and are much easier to control. As such, direct contact between two people is rarely considered as a parasitic diseases mode of transmission, with respect to the possible exceptions exemplified below.
Although it is not considered as a frequent mode of transmission for parasitic diseases, different sex practices are considered as the only possible way to acquired parasites by direct contact with an infected person. Actually, all other types of direct contacts between two individuals are not considered as a transmission mode of parasitic diseases.
As such, the protozoan parasite Trichomonas vaginalis is considered to be a major exception as it is the only parasite almost exclusively transmitted by direct contact. Actually, this parasite is mostly acquired when a healthy person have unprotected sexual intercourse with an infected person. Actually, this parasite is responsible for a very common sexually transmitted disease in developed countries.
Even though it is not considered as a widespread mode of transmission, it is also possible to acquire intestinal parasites usually transmitted by the fecal-oral route during unprotected anal intercourse or oral-anal contact between infected and uninfected people. Among others, infections caused by Cryptosporidium, Entamoeba histolytica and Giardia intestinalis are susceptible to be acquired by these means.
Some intestinal parasites usually acquired via the fecal-oral route can also be transmitted from one person to another by indirect contact. These parasites usually required that something contaminated by faeces containing parasite’s eggs be put in contact with the mouth. Lack of hygiene, such as improper hand washing after going to the bathroom, is the major condition required to acquire this type of parasites indirectly from another individual. For example, it could occur when a person caring for another one suffering from intestinal parasites gets accidentally infected. It is also more frequent with children as they put more frequently stuff in their mouth and are susceptible to acquired parasitic diseases by putting their hands or toys contaminated by one of their little friends in their mouth. Furthermore, it could also occur when an infected worker in a kitchen contaminate food by lacking of hygiene, for example by manipulating food after going to the bathroom without proper hand washing. By extension of this concept of indirect means to acquired parasitic diseases from an infected person, lack of sanitation in some countries allowing water contamination with infected human faeces can be considered as a very indirect mean to get an intestinal parasite from someone.
Another indirect person-to-person parasite mode of transmission is from needle sharing occurring frequently with intravenous drug-users. As such, this mode of transmission is possible but quite rare. Some bloodstream parasites, such as Plasmodium, the causative agent of malaria, are susceptible to be acquired from needle sharing.
Source: Centers for Disease Control and Prevention
