The Life Cycle of Cryptosporidium parvum

The life cycle of C. parvum will be analyzed on this page. The figure at the right helps to explain the different stages of life for C. parvum and will be referred to as to help better explain the life cycle of this organism. First, we can notice that Cryptosporidium parvum has an zygotic life cycle. In a zygotic life cycle, the organism has a unicellular diploid stage. The unicellular, diploid stage is the oocysts, and is looked for in determining if an environment has been effected with or contains with C.parvum.
    In stable conditions, such as in contaminated water or fecal waste, oocysts of Cryptosporidium parvum are found (Xiao et. al, 2004). An oocyst is a zygote of a parasitic organism contained inside a fluid filled capsule or tough outer membrane. The oocyst is the resting stage of an organism. An oocyst will be what is referred to as stage 1 (as shown in figure 1.1). Until an oocyst is ingested by a living organism, it will remain in stage 1.
    The second stage of C. parvum is to contaminate an environment in which it might become in contact with its host who will provide it nutrients to survive and and a protected environment to reproduce. This may happen through poorly treated pools, lakes, river, or public water. A case in Milwaukee, WI in 1993, 400,000 people became ill after they drank contaminated public water (Xiao et. al, 2004).  It is especially threatening for people with HIV or AIDS. C. parvum also infects other animals, but most commonly farm animals including cows, goats, sheep, and pigs. Stage 3 of the C. parvum (as shown in figure 1.1) is the stage at which an individual organism has ingested the protozoan parasite. About 24 Oocyt and sporozoites of C. Parvum published by Margaret Davidson (2003).hours after ingestion the oocysts open to release sporophytes Stage 3-a. This process is known as excystation or defined as an escape from a cyst (Borowski et al., 2009). A sporophyte attacks a host cell (such as a human cell) about five minutes* after excystation, and after 48 hours all oocysts have opened. The sporophyte then develops into a trophozoite; the stage (3-b) of life where a parasite acquires nutrients from its host cell (Borowski et. al., 2009).
    Asexual reproduction begins when the trophozoite stage 3-d,e,f divides to form two meront. Meronts are haploid cells of C.parvum that reproduce asexually, and do so rapidly. This stage has been observed as early as 24 hours after ingestion of the oocyst . It has also been shown that meront I, which is the first generation haploid stage of C. parvum, are smaller in size and appear to have a thinner membrane then meront II, which is a second generation haploid stage of C.parvum (Borowski et al., 2009). When merozoites (unicellular haploid cells) produced from meront II grow and develop, they form micro- or macrogamonts, which are gametes preparing to undergo sexual reproduction(stage 3-g,h). At this stage, the micro- or macrogamonts are less connected to the host cell and more extracellular (Borowski et. el., 2009.  Sporozoites breaking out of oocyst (2004).
    Sexual reproduction occurs when a microgamont and macrogamont undergo fertilization (stage 3-i). Together they form a zygote and grow into an oocyst that can leave the host organism through fetal waste or maintain the parasitic life cycle. This process can take about 4 days (Borowski et. al., 2009). This means that C. parvum can successfully live inside of a host, such as a human for many days if they are not treated. Sexual reproduction allows for C.parvum to exchange genes and evolve better to its parasitic environment. These new oocysts (formed through sexual reproduction) are believed to be largely responsible for the life-threatening diseases of immunodeficient persons (Xiao et. al, 2004).

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*Time predictions are those provided by a study done on studied life cycles of C. parvum by H. Borowski, R.C.A. Thompson, T. Armstrong, and P. L. Clode. Look at references

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