Introduction:
Cyclospora is an intracellular, single-celled sporozoan with a diameter of around 8.6 ÎĽm. When someone consumes food or water contaminated with the parasite, they become infected.
It cannot transmit from one person to another as the oocysts in the faecal matter require a certain days and temperature for sporulation and becoming infective. The infected person can excrete the protozoa in faeces, even when they are asymptomatic or even after their symptoms have started to subside.
Lifecycle of Cyclospora cayetanensis:
The oocyst is double-layered. The oocyst released in the feces is not immediately capable of causing infection. It must first undergo a developmental process called sporulation, which occurs outside the host in the environment. The interior cell called the sporont divides to create two sporocysts during this phase, and each sporocyst contains two thin sporozoites, for a total of four.
When a new host ingests these sporulated oocysts, the protective layers are broken down in the small intestine, allowing the sporozoites to emerge. These active forms then penetrate the epithelial lining of the intestine. Inside these cells, the parasite undergoes a stage of rapid asexual reproduction, known as merogony, producing two types of meronts. Type I meronts, which multiply and produce more invasive stages to continue the cycle of infection. Type II meronts, which transition the parasite into the sexual phase of its lifecycle.
Merozoites from type II meronts lead to the formation of macrogametocytes. Gametocytes fuse to give rise to an oocyst, which is defecated by the host.
Fig: Lifecycle of Cyclospora cayetanensis
Source: CDC 2019
Pathogenesis:
In humans, C. cayetanensis completes both its sexual and asexual phases. Cyclosporia generally targets the small intestine. However, extraintestinal forms of disease can occur. Infection by Cyclospora begins when sporozoites bind to the surface of enterocytes, invade these intestinal cells, undergo asexual replication, and then extend the infection to neighboring cells within the villi and crypts. The pathological changes result in the loss of membrane-bound digestive enzymes and diminish the surface area of the intestine, leading to diarrhea and a decreased uptake of electrolytes, water, and nutrients. Cyclosporiasis can be particularly challenging in immunocompromised individuals, e.g., patients undergone an organ transplantation and are undergoing immunosuppressive treatment.
Laboratory diagnosis:
Wet Mount and Concentration Methods
Several stool samples (over a 10-day duration) need to be tested to ensure the infection with C. cayetanensis. It is possible to find C. cayetanensis oocysts using wet smears, either with or without iodine.
Concentration procedures, such as formalin-ether sedimentation or flotation with a sucrose solution, might be employed.
Additional microscopic techniques are needed to rule out amoeba or inflammatory cells and attain a greater detection sensitivity.
Modified Acid-Fast Staining
Acid-fast lipids are present in the oocyst walls of coccidian parasites like Cyclospora. Because of this shared characteristic, acid-fast (ZN) staining is useful for screening all three parasites in a single test. For detection, modified ZN staining with 1% H2SO4 as the decolorizer is employed. Heated Safranin Staining. The original purpose of this staining was to identify Cryptosporidium. Oocysts of Cyclospora have a striking reddish-orange hue.
Auto Fluorescence
The Cyclospora oocysts exhibit autofluorescence. The pronounced auto-fluorescence of Cyclospora oocysts is a valuable characteristic for their identification under a microscope. Under light excitation at 450–490 nm, they emit a green fluorescence, while exposure to UV light at 365 nm produces a blue glow.
Fig: Cyclospora cayetanensis oocysts under (C) acid-fast stain and (E) UV fluorescence microscopy are shown in the figure.
Source: Almeria, S., Cinar, H. N., & Dubey, J. P. (2019)
Serological tests
Commercial serological assays to detect human exposure to Cyclospora are currently unavailable, even though serological screening for Cyclospora would aid epidemiological studies, particularly in epidemic investigations.
Although certain IgG and IgM antibodies have been evaluated using enzyme-linked immunosorbent assays to describe human serological immune responses to cyclosporiasis, precise infection diagnosis at the patient level has not been accomplished.
Molecular Diagnostics (PCR-based Methods)
Numerous multiplex PCR tests (together with other parasites) including conventional, nested, and quantitative PCR (qPCR) methods have been developed in recent decades for the identification of Cyclospora.
Prevention and Control Measures:
- Health education, effective personal cleanliness,
- Preventing children from geophagia,
- Drinking boiling or bottled water,
- Avoiding raw products, having adequate sanitary infrastructure, and treating human waste are all ways to prevent or control cyclosporiasis.
Prevention and control can be assisted by killing or removing oocysts from water or fresh foods. Since oocysts of Cyclospora are resistant to many disinfectants used in traditional water treatment plants and are difficult to remove from water, physical treatments (e.g., membrane filtration), ultraviolet disinfection, or managed aquifer recharge are possible approaches for their removal.
References:
- Almeria, S., Cinar, H. N., & Dubey, J. P. (2019). Cyclospora cayetanensis and Cyclosporiasis: An Update. Microorganisms, 7(9), 317. https://doi.org/10.3390/microorganisms7090317
- Centers for Disease Control and Prevention. (2019). Cyclosporiasis.
https://www.cdc.gov/dpdx/cyclosporiasis/index.html