Host: Infection, Transmission & Diseases

Parasites specifically seek out a host to reproduce. Usually, the host feeds the parasites but does not die. Nevertheless, unpleasant symptoms occur, necessitating treatment.

What is a host?

The goal of a parasite or pathogen is to increase its population. To do this, the host provides optimal conditions, such as sufficient food and shelter. Different types of host exist. The main host is the type that offers the pathogen the best conditions. Accordingly, a parasite strives to reach such a host. The secondary host also offers appropriate living conditions. However, these are worse than those of the main host, so that a parasite can develop worse. In the case of a false host, there is no possibility of survival at all. Depending on the parasite, host switching may occur. The host in which sexual reproduction occurs is called the final host. In the intermediate host, the parasite reproduces asexually. The transport host transmits the parasite. He himself is not infected. In the occasional host, the pathogen can develop, but it prefers another host, so that the occasional host is rarely infected. Parasites are not only tapeworms and mosquitoes. Bacteria, viruses and fungi also reproduce in this way and reach other hosts by different routes.

Occurrence, distribution and characteristics

The way a host is infected depends on the particular pathogen. In particular, bacteria are often passed by smear or droplet infection. In smear infection, infection can occur even when an infected person is not present. Instead, the infection occurs via surfaces that are contaminated with the pathogens. For example, the germs travel by touching a door handle. Contaminated drinking water can also play a role. In the context of direct infection, the germs travel on through physical contact between people or people and animals – for example, by shaking hands. In the case of smear infection, the bacteria can be passed on primarily due to poor hygiene. Most pathogens are excreted in the stool. Unwashed hands after going to the toilet can spread the bacteria. Droplet infection, on the other hand, occurs via droplets of secretion. These escape from the respiratory tract and in this way infect people who are in the vicinity. Thus, an unprotected cough, sneeze or snort can spread the bacteria in the room. Tapeworms, on the other hand, enter the gastrointestinal tract through contaminated food. This includes, above all, fruit and vegetables that have not been washed and meat that has not been cooked sufficiently. Particularly in tropical regions, mosquitoes transmit various parasites. Although humans serve only as intermediate hosts in malaria, for example, the infection triggers severe symptoms.

Significance and function

A parasite does not usually kill its host. To do so would deprive it of its own livelihood. Instead, it uses the organism to reproduce, develop, and spread. Nevertheless, health disadvantages arise for the host. Some of these become noticeable relatively quickly, while in other cases they remain undetected for a long time. The extent to which the health of the affected person is attacked depends largely on the underlying pathogen. Already in early childhood, humans serve as hosts for various pathogens. These include, for example, bacteria and viruses that trigger colds or gastrointestinal complaints. A strong immune system can usually banish the invaders on its own within a short period of time. If the body does not succeed in such a procedure, antibiotics or medications that promote the coughing up of mucus, for example, help in the case of a bacterial illness. Less harmless, however, are other parasites that use the affected person as a host. Malaria, for example, cannot be destroyed by the body’s own defenses. The pathogens are transmitted by the bite of an infected mosquito. The parasite then attacks the red blood cells and multiplies in them. During the typical attacks of fever, the blood cells burst, allowing the parasites to spread and multiply further. If left untreated, malaria can lead to death.Therefore, it is important to see a doctor at the first signs.

Diseases and complaints

Some of the parasites can cause complications. For example, roundworms cause fever and manifestations reminiscent of asthma as soon as they approach the lungs. In the intestinal area, affected individuals suffer from abdominal pain. Sometimes, due to the worm infestation, there is an obstruction of the intestine or bile duct. Such an occurrence results in further complaints, such as colicky abdominal pain, increased gas accumulation and a lack of bowel movements. Trichinae, on the other hand, are initially noticeable through nausea, vomiting or watery diarrhea. However, they can also spread to the muscles, possibly causing myocarditis. The bovine and porcine tapeworm can get into the appendix or the pancreas and cause inflammations, sometimes with a severe course. By ingesting tapeworm eggs, the pathogens multiply in the intestine, blood vessels, muscles and organs. Under certain circumstances, cysticercosis develops. This in turn results in blindness in some patients. Complications are also possible in the course of a bacterial infection that leads to cold symptoms. These usually occur more frequently if the illness is not sufficiently cured. Particularly in children, the pathogens can migrate to the ear, where they manifest as otitis media.