4 Obligate Parasite: Detailed Facts Around It

Parasite are the organism that tend to love inside or on the other animal for its survival and this relation is called or be parasitism.

The obligate parasite is the one where the organism is not able to complete the cycle pf life without getting to exploit the host in particular. The obligate parasite is also called the holoparasite and also are not able to make a host if in case they lack to reproduce.

Parasite is a type of symbiosis and takes place between host and the parasite. The parasite is any organism that gets help from the relation and thus also tend to derive the advantages at the use of the host. Thus obligate parasite also depends in it being all or partially obligate parasite on host to get itself complete the life cycle. The [parasite that is complete based on the host is said to be obligate parasite.

The parasite that do not completely tend to depend on the host is called to be facultative ones. As for the reason of it being an obligate parasite, the host is kept alive and is vital to do so as the obligate parasite requires the host for growing and also for reproduction at the same time. The exception for obligate parasite takes place at the time of death while it keeps the transmission of parasite into work to other host.

Mostly the obligate parasite needs the host to stay active or alive in order for its survival. If it is placed far from the host it could lead to the obligate parasite being dead. For its, nourishment, survival, habitat and reproduction the obligate parasite is relied on the host. It shall die without it. On the other hand, the parasite that is facultative shall also live without the host as it is not linked completely with host with sometimes becoming a parasite under certain areas.

obligate parasite
Image credit- Animal obligate parasiteWikipedia

Virus are the best example for obligate parasite. They tend to not reproduce at the outer part of any cell alive. Thus, they are said to be an intracellular obligate parasite. The choose to infect the host cell and also tend to use its genetic machine to make energy and also synthesizes the proteins making it to replicate. It is also vital for the obligate parasite to be compatible to the host for its shall lead to its death.

The obligate parasite has the capacity to change the dynamics and also have a stricture of the host but still the area of host can be of much affect to the obligate parasite. One can understand the link between the obligate parasite a host by seeing the difference of host and obligate parasite yet by being able to compare such variety with rest area might influence the bond shared.

Life cycle

There can be two cycle yet that has been discovered for the obligate parasite and either of them is followed by all examples of it.

The first cycle for the obligate parasite is the direct life cycle and the other is the complex or the indirect cycle of life. The life cycle that is direct tends to be called so when obligate parasite infects one host species and indirect is the opposite.

On the other hand, the complex or the life cycle that is indirect is the one where the parasite infects more than one of the host species. One example of this type of obligate parasite can be the plasmodium which is a protozoon that tend to cause malaria inside the humans and also the parasitic mosquito that helps them use the vector to reach the humans and then take the host to be definite.

Parasites are typically introduced by the bite of an infected Anopheles mosquito. These introduced parasites, called “sporozoites”, follow the bloodstream to the liver obligate parasite where they invade hepatocytes. They grow and divide in the liver for 2–10 days, with each infected hepatocyte eventually harboring up to 40,000 parasites. The infected obligate parasite hepatocytes break down, releasing this invasive form of Plasmodium cells, called “merozoites” into the blood stream. In the blood, the merozoites rapidly invade individual red blood cells, replicating over 24–72 hours to form 16–32 new merozoites. 

Image credit-MalariaWikipedia

The direct life cycle of the obligate parasite is simple and thus not include many steps. Yet on the other part, the indirect cycle infects the host that is intermediate or secondary. It only takes a short time for the entire process to get complete and takes place in many transitions mode. It is so as the obligate parasite reached the stage of maturity which means it’s is able to reproduced and able to parasitize the definitive host or the primary host making it a good obligate parasite.

Image credit-ParasitismWikipedia

Some of the parasites that are obligate parasite tend to spend its while life cycle on the host. A good example for this is the head louse also termed to be the Pediculus humannus capitis. This is an insect that is obligate parasite and is ecto to the humans, they thrive and also most spend its whole life on the human making it a host. Thus they are the obligate parasite that are permanent. They however cannot survive outside the host for more than a day.

There are also many obligate parasite that do not spend its life on the host being the hookworm. It is also called the Necatior americanus that spends the part of its life in soil and then make human the host with obligate parasite penetrating the skin. The ecto obligate parasite are seen outside the body of host like the ticks. The endo obligate parasite are ones that live in the body of host like the fluke. There are also the Brood ones that do not have any contact with host but raised by them like cuckoo.


An obligate parasite in plants is the hemp broomrape that attacks the crops like tomato and tobacco for help or growth.

Some of the obligate parasite that are plants live in host all while without making themselves in eye and are only visible if they need to be a flower. Any example of obligate parasite is the Rafflesia which is an endo obligate parasite and appears in the type of a single big flower.

These plants tend to use roots to draw its nutrition Rafflesia is also called as Tetrastigma vines and has no leaves, roots or stems. It gets its nutrients absorbed by haustorium that is inside the tissue of the vine host. It has big flowers and the buds rise from ground or also directly from the low stems of the host plants. One of its species has the largest flower in the world. Parasites which are dependent on the host for completing their life cycle are called obligate parasites.

The flowers look and smell like rotting flesh. The foul odour attracts insects such as carrion flies, which transport pollen from male to female flowers. Most species are dioecious, having separate male and female flowers, but a few being R. baletei and R. verrucosa have hermaphroditic flowers.  Little is known about seed dispersal. Tree shrews and other forest mammals eat the fruits. The extremely tiny seeds have extremely tiny elaiosomes, and are thus most likely dispersed by ants. The seeds are packed into berries, which contains hundreds of thousands of seeds.

Image credit- RafflesiaWikipedia

Witchweed is an example of obligate parasite plant that has ability to take its need from host and is few cases damages the host or it beneficial to it. The structure that defines the obligate parasite plant is the haustorium that penetrates the host and makes a union vascular in nature on the plants. The obligate parasite is different from the aerophytes, the lianas, the epiphytes and the vines which later are balanced by the rest plants as they use others to grow. Parasites which are not dependent on the host for completing their life cycle are called facultative parasites.

Striga bilabiata MS4167.jpg
Image credit-WitchweedWikipedia

Round worms

Many roundworm parasitic diseases are caused by poor sanitation and hygiene. Most roundworms or their eggs are found in the dirt and can be picked up on the hands and transferred to the mouth.

Roundworms (also called nematodes) are worms with a long round body. They vary in length from several millimetres to up to two metres. Roundworms are common obligate parasite in warm tropical countries. Children are more often affected than adults. The spread of infection is also increasing in line with increased travel and mobility.

Roundworm eggs and tiny young worms (larvae) live in the soil. They most commonly get into the body when a person gets them on his or her hands and then transfers them to the mouth. Some can also get into the body through the skin making t a good example for the obligate parasite. The number of roundworm infections throughout the world is generally increasing but varies according to levels of poverty, natural disasters and human conflicts.


Not all the bacteria are much infective and thus are also not obligate parasite. There are few of these around us.

There are also many reference that do not consider the bacteria to be obligate parasite despite being pathogen or infective. Bit for rest they are obligate parasite with some of the examples being the staphylococci and the streptococci.

In the nature there are few of them that are obligate parasite and thrive in nature with or without the host. The ones that are infective or are pathogenic on the other part may be said to be apart from obligate parasite on the grounds that that depend in the host for its nutrition and survival and also to get itself protected. Around the outside of the cell membrane is the cell wall. Bacterial cell walls are made of peptidoglycan also called murein, which is made from polysaccharide chains cross-linked by peptides containing D-amino acids.

Prokaryote cell with structure and parts
Image credit-BacteriaWikipedia

An obligate parasite that is Treponema pallindum grows in a cell for animal as it needs to be low level of oxidation and also reduction and less oxygen level tension. Mostly the obligate parasite is linked with pathogenic bacteria and is mostly seen in the host. The microbe is said to be obligate parasite and cannot multiply on its own. They lack the capacity of cell. Thus they keep its help expectation from host. Some obligate parasites may spend their entire life cycle on their host.

Some bacteria are obligate parasite and grow only within a living host cell. Rickettsia and Chlamydia, for example, grow in eukaryotic cells, and Bdellovibrio grow in bacterial cells. Treponema pallidum is difficult, if not impossible, to grow in culture, probably because it requires low oxygen tension. The fundamental source of energy in almost all ecosystems is radiant energy from the Sun. The energy of sunlight is used by the ecosystem’s autotrophic, or self-sustaining, organisms.

Slice from electron cryotomogram of Bdellovibrio bacteriovorus cell.jpg
Image credit-BdellovibrioWikipedia

Bacteria do not have a membrane-bound nucleus, and their genetic material is typically a single circular bacterial chromosome of DNA located in the cytoplasm in an irregularly shaped body called the nucleoid. The nucleoid contains the chromosome with its associated proteins and RNA. Like all other organisms, bacteria contain ribosomes for the production of proteins, but the structure of the bacterial ribosome is different from that of eukaryotes and archaea. They won’t be able to survive outside their host for more than 24 hours.

Under a light microscope, host-dependent Bdellovibrio appears to be a comma-shaped motile rod that is about 0.3–0.5 by 0.5–1.4 micro metre in size for obligate parasite with a barely discernible flagellum. Bdellovibrio show up as a growing clear plaque in an E. coli “lawn”. Notably, Bdellovibrio has a sheath that covers its flagellum – a rare feature for bacteria. Flagellar motion stops once Bdellovibrio has penetrated its prey, and the flagella is then shed. Host-independent Bdellovibrio appear amorphous, and larger than the predatory phase.

Vampire bats

They are the species of the Desmodontinae family and ae seen in South f America and the Central of it.

It is a good example of obligate parasite and the source of its food is blood which gives them a dietary train known as hematophagy. There are three of its species that feed only on blood which is the common obligate parasite among it.

They are also native to the Chile, Argentina, Brazil, Uruguay and Mexico. With having differences in these each of them are in separate genus with each having one obligate parasite species that is extinct. The three known obligate parasite of this type are all same with the one that feed on blood one time evolved only once with all sharing same ancestry. Necator americanus, will spend part of its life cycle in the soil and then parasitizes a human host by penetrating the skin.

The image depicts the common vampire bat (i.e. Desmodus rotundus) hanging from a cave wall and staring at the camera.
Image credit-Vampire batsWikipedia

 The name for this obligate parasite is so because of their high protein diet, vampire bat researchers can locate roosts by the pungent ammonia aroma produced by their feces. The bats were named after vampires, not the other way around. Vampire mythologies existed in various cultures around the world long before before vampire bats got their name. Vampire bats have burnt amber colored fur on their backside while soft and velvety light brown fur that covers their belly. Other obligate parasites need not spend their entire life cycle inside their host.

They are the obligate parasite with sharp teeth good for piercing and basically feed in the ecto obligate parasite of the bigger mammals and also feed mammals themselves. They also attack insects that are wounded by animals and feed on wounds and prey on small vertebrates. They are the obligate parasite that are omnivores and begin to digest blood and also flesh from sites of bigger animals that are harmed. Vampire bats have a wingspan of about 8 inches and a body about the size of an adults thumb.


I am Ankita Chattopadhyay from Kharagpur. I have completed my BTech in Biotechnology from Amity University Kolkata. I am a Subject Matter Expert in Biotechnology and also a web content writer (freelancer). I have been keen in writing articles and also interested in Literature with having my writing published in a Biotech website and a book respectively. Along with these, I am also a Hodophile, a Cinephile and a foodie.

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