Possible parasites include nematodes, copepods, protozoa, and helminths. Some eukaryotic organisms, including a number of protozoa and helminths, are human parasites. Detected pathogens include helminths, cryptosporidium, different types of bacterial infections, and other unidentified parasites. Some eukaryotic organisms, such as protists and helminths, cause disease. Pigs can be carriers of various helminths, such as roundworms, pinworms, hookworms. In general, Th2 responses are more effective against extracellular bacteria, parasites including helminths and toxins. Many of the worms referred to as helminths are intestinal parasites. Internal parasites found in waterbuck include tapeworms, liverflukes, stomachflukes and several helminths. Scientists are also searching for a vaccine against helminths, such as a hookworm vaccine. American marten host several internal and external parasites, including helminths, fleas (Siphonaptera), and ticks (Ixodida). Large parasites like helminths are too big to be engulfed and killed by phagocytosis. However, in some cases helminths and other parasites are a cause of developing allergies instead. In Israel, some jackals are infected with intestinal helminths and "Leishmania tropica". Infections with helminths may alter the autoimmune response that causes the disease. It is observed in certain cnidarians and helminths.