Difference Between Ova and Cyst

Main Difference – Ova vs Cyst

Ova and cyst are two reproductive structures of parasites found in the stool of the host. Both ova and cyst can be ingested through drinking water and food contaminated with feces of an infected individual. Parasites enter into the gastrointestinal tract of the host animal via the fecal-oral contamination. The life cycle of the worm-like parasites is composed of the eggs/ova, larva, and adult. The parasitic protozoa lifecycle is composed of the trophozoite and the cyst. Both ova and cyst are the propagation stages of parasites. The main difference between ova and cyst is that ova are a life stage of parasitic worms whereas cyst is life stage of parasitic protozoa.

Key Areas Covered

1. What are Ova
     – Definition, Facts, Structure
2. What is a Cyst
     – Definition, Facts, Structure
3. What are the Similarities Between Ova and Cyst
     – Outline of Common Features
4. What is the Difference Between Ova and Cyst
     – Comparison of Key Differences

Key Terms: Cyst, Encystation, Larva, Ova, Parasites, Protozoa, Reproduction, Trophozoite, Worms

What are Ova

Ova are eggs of parasitic worms that occur in the feces as an indicator of parasitic disorders. Typically, worms lay eggs during reproduction. Some of the worms such as tapeworms and flukes are hermaphrodites while others such as roundworms are unisexual. Different types of ova of parasitic worms are shown in figure 1.

Figure 1: Ova Types

Typically, a worm may deposit a thousand of ova daily. The ova consist of a strong shell, protecting them from unfavorable environmental conditions. The shell is made up of three layers: outer proteinic later, middle chitinous layer, and inner lipoidal layer. So, these ova are viable for 1 – 2 months in sewage, soil or fresh water. They can enter into the host through fecal-oral contamination. The larva hatches from viable ova inside the host in most parasitic worms.  

What is a Cyst

A cyst refers to a resistance stage of a protozoan that helps to survive in unfavorable environmental conditions. As the cyst is the propagation stage of the parasitic protozoa, it is infectious. Encystation refers to the process of formation of the cyst. It takes place in the rectum of the host. Therefore, cysts can be identified in the feces. Cysts are spherical structures. They are covered with a hard cyst wall with two layers. The contractile vacuole, macronucleus, and cilia are visible in young cysts. The organelle structures of the old cysts are granular. The metabolism and motility are arrested in cysts. A cyst is shown in figure 2.

Figure 1: A Cyst

The growing and reproductive stage of the cyst is the trophozoite. The formation of the trophozoite from a cyst is referred to as the excystation. The excystation takes place in the large intestine of the host at the subsequent ingestion of the cyst by the host. Trophozoites are not resistant structures. Generally, trophozoites are covered with cilia. Hence, they are motile. They exhibit rotary or boring motility. They absorb nutrients from the host and reproduce inside it.

Cysts also occur in bacteria and nematodes. In bacteria, cysts are less resistant than spores. They allow the dispersal of bacteria. They germinate in the favorable environmental conditions. The cysts occur in plant-parasitic nematodes as a part of their lifecycle.

Similarities Between Ova and Cyst

• Both ova and cyst are the propagation stages of parasites.
• Both ova and cyst can be identified in the stool of infected individuals.
• Both ova and cyst can be either round, oval, triangular, square or d-shaped.
• Both ova and cyst are infectious.

Difference Between Ova and Cyst

Definition

Ova: Ova refer to the eggs of parasitic worms that are found in the feces as an indicator of parasitic disorders.

Cyst: A cyst refers to a resistance stage of a protozoan that helps to survive in unfavorable environmental conditions.

Significance

Ova: Ova are the propagation stage of parasitic worms.

Cyst: Cyst is the propagation stage of parasitic protozoa.

Size

Ova: The size of the ova is typically large.

Cyst: The size of the cyst is small.

Thickness of the Wall

Ova: The ova consist of a thick wall.

Cyst: The cyst consists of a thin wall.

Filled with

Ova: The ova are filled with cytoplasm and nucleus.

Cyst: The cyst is filled with fluid, so, it is more fragile.

Conclusion

Ova and cyst are two propagation stages of parasites. Ova are the propagation stage of parasitic worms while cyst is the propagation stage of the parasitic protozoa. Both of them can be found in the stool of the infected individuals. The main difference between ova and cyst is the type of organisms in which each propagation stage occurs.

Reference:

1. “Ova and Parasites (Stool).” Ova and Parasites (Stool) – Health Encyclopedia – University of Rochester Medical Center, Available here.
2. Berkey, The. “Microbial Cysts in Drinking Water – Why Do We Have to Know About It.” The Berkey, Available here.

Image Courtesy:

1. “Collage of various helminth eggs” By SusanA Secretariat Catalina Maya Rendón –  (CC BY 2.0) via Commons Wikimedia
2. “Entamoeba histolytica 01” By Photo Credit:Content Providers(s): CDC/ Dr. George Healy –  Centers for Disease Control and Prevention’s Public Health Image Library (PHIL) (Public Domain) via Commons Wikimedia