Cyclosporiasis and Africa - should we be concerned?
Cyclosporiasis is a diarrhoeal disease caused by the protozoan pathogen
Cyclospora cayetanensis1. It is considered an emerging disease of public health concern primarily in the developed countries where it has been identified as the cause of several outbreaks in North America and Europe, and with traveller's diarrhoea
2–6. In these countries, cyclosporiasis transmission has primarily been linked to foods imported from developing countries adding impetus to the review of food import regulations with far reaching implications on developing country economies that depend on North-South trade in agricultural produce
4–9. The transmission of the disease in the developing South where
C. cayetanensis is endemic, remains little understood but has been associated with water and sanitation in Nepal, Guatemala, Nigeria and Egypt
7, 10, 11.
Ashford is credited with having first identified C. cayetanensis as a human pathogen in 1979 in Papua New Guinea12. Thereafter, the parasite remained largely uninvestigated and it was not until 1994, when the first detailed morphological description and naming of Cyclospora cayetanensis was done1. Few studies have been carried out since then to determine the transmission and epidemiology of cyclosporiasis in Africa and its public health impact on the continent. The disease has been reported in Nigeria, Tanzania and Egypt13–15. Although it is thought to be self-limiting in immuno-competent individuals, cyclosporiasis can cause prolonged diarrhoea that could be life threatening in immuno-compromised patients. Moreover, like other coccidian parasites, C. cayetanensis has been associated with various sequelae including biliary disease, aculculous cholecystitis, Guillain-Barré syndrome and reactive arthritis syndrome following prolonged infection16–19.
The study of cyclosporiasis is rife with difficulties that have largely contributed to its underreporting in Africa and little public awareness20. A key contributor to this is the specialised staining methods for diagnosis that are not routinely carried out in clinical laboratories20–22. Additionally, efforts to elucidate its transmission and biology in endemic areas is impeded by lack of sensitive and specific methods for Cyclospora detection in the environment, agricultural produce and water bodies and further compounded by the lack of a suitable animal-model23–26. Cyclosporiasis has therefore remained a little known disease albeit with potentially far reaching impact on the health and economy of developing countries due to its impact on the horticulture industry as a food borne pathogen. Several publications pertaining to the methods of diagnosis and detection exist and have been ably reviewed by others9. Our aim is to bring this disease to the attention of African health researchers and to highlight potential areas of study in our likely endemic setting.
History of Cyclosporiasis
According to Lainson
27, it was Eimer who as early as 1870 first described an organism in intestines of the mole
Talpa europaea that was eventually characterized and named
Cyclospora caryolytica by Schaudinn in 1902
28. But
C. glomericola, observed in the millipede, was the first species to be classified as
Cyclospora by Schneider who established the genus in 1881
29. So far
C. glomericola is the only species out of a total of 19
Cyclospora species identified to date to be encountered in an invertebrate host, the rest being found in reptiles (snakes) and mammals (rodents and non-human primates)
27.
It was not until the 1970s that cyclosporiasis first came to medical attention when an un-described coccidian was associated with diarrhoea in Papua New Guinea4, 12. Thereafter, endemic cases were also reported in Haiti, Nepal, Peru and linked to Travellers Diarrhoea in the 1980s, where it was reported variously as Cryptosporidium muris-like, a flagellate, an unsporulated coccidian, a large Cryptosporidium, a blue-green alga (cyanobacterium-like body), or a coccidian-like body4,30. By 1990 the new pathogen was associated with chronic diarrhoea in acquired immunodeficiency syndrome patients 31. Nevertheless, it was not until the 1990s that food and water-borne outbreaks in North America grabbed public and scientific attention to the emergence of the disease, after a food or waterborne outbreak of 21 was reported in a Chicago teaching hospital in 199032.
This fuelled efforts to definitively identify and characterise the pathogen, with the first breakthrough occurring in 1992 when Ortega et al., reported they had sporulated and excysted the oocysts, thus ending speculation on the classification of the parasite and placing it in the genus Cyclospora33. The same group finally identified and characterised the causative agent as the coccidian Cyclospora cayetanensis (Apicomplexa: Eimeriidae) using classical morphological methods1, 30. However, molecular techniques have placed the pathogen closer to Eimeria species, suggesting its classification as such34, 35. Today, C. cayetanensis transmission in developed countries through food and water borne outbreaks has been well documented and understood, however the modes of transmission and risk factors in endemic areas remain poorly understood4, 36, 37.
Life cycle and Biology
Cyclospora cayetanensis is an obligate intracellular parasite that is normally found in the jejunum. Oocysts found in the stool can be mistaken for the common
Cryptosporidium spp. infecting humans, but can easily be distinguished by their larger size (8–10 µm) using an ocular micrometer
38. The life cycle begins with the ingestion of the sporulated oocyst in contaminated water or food. Unlike
Cryptosporidium, this oocyst when freshly passed in the stool is not sporulated and therefore not infective
1, 30. Oocysts require a few days to weeks, depending on climatic factors, to develop and mature in the environment into the infective sporulated oocyst, thus precluding direct fecal-oral transmission
1, 38. Temperatures ranging between 25–30°C are most suitable for sporulation. Upon being ingested, the oocysts excyst in the gut, releasing the sporozoites, which proceed to invade the epithelial cells of the small intestine
39, 40. The sporozoites undergo two generations of asexual reproduction in the cell, whereby they form meronts that contain numerous merozoites
40. The first generation meronts have 8–12 merozoites, whilst the second have only 4 merozoites, which penetrate new cells to form gametes. Some of these gametes enlarge to form the female macrogametes and some microgametes that undergo meiosis to form numerous flagellated sperm-like microgametes. The mature microgametes leave the microgametocyte and migrate to fertilize the macrogamete. The development of a resilient oocyst wall around the zygote, which contains 2 sporocysts or small oocysts, makes up the unsporulated oocyst. Eventually the oocyst is passed out with stool to begin the process of sporulation. Sporogyny commences in the presence of higher atmospheric oxygen concentrations and is complete between 7–12days
40–43.
Clinical aspects of C. cayetanensis infection Presentation
The clinical presentation of
C. cayetanensis may include gastrointestinal (GI) symptoms such as loose or watery diarrhoea, nausea, vomiting, abdominal cramps, loss of appetite, or unintentional weight loss; or constitutional symptoms such as fever, chills, muscle aches, joint aches, generalized body aches, headache, or fatigue
8. Although asymptomatic infections are known to occur, the onset of symptoms in naïve populations observed in outbreaks is 1–14 days post exposure and is often accompanied by a characteristic waxing and waning of symptoms
6, 40, 41, 44. In endemic countries, symptoms begin approximately 5–8 days after and may persist for a month or more. However, infection without watery diarrhoea is a common occurrence and has been observed in Haiti among other areas
45.
Diagnosis
Detection is based on the identification of oocysts in stool specimens using modified acid fast staining, or hot safranin test
21. Where cyclosporiasis is suspected, up to 3 stool specimens taken 2 days apart should be tested to rule out the parasite. A rapid method of identification is possible on wet mounts using fluorescent microscopy employing a filter with a wavelength in the range of 340–380 nm, which reveals the bright, pale blue oocysts glow
30. Polymerase chain methods (PCR) have also been developed for diagnosis and detection in the environment, but the primers appears to cross react with
Eimeria spp.
26, 35, 46.
Differential diagnosis of cyclosporiasis includes all other causes of diarrhoea. Infections with Giardia, Cryptosporidium, Isospora, Toxoplasma and Microsporidia should be suspected in cases of persistent diarrhoea that does not respond to the usual treatment (6, 20, 31, 36, 41, 47. Cyclosporiasis can also present symptoms closely resembling celiac disease and irritable bowel syndrome 48.
Sequelae
Like cryptosporidiosis,
C. cayetanensis infection has also been associated with the onset of various extra-intestinal complications that may accompany prolonged infection, especially in the HIV immunocompromised patients. These include acalculous cholecystitis
19; biliary disease
18, Guillian-Barré syndrome
17, and Reiter or reactive arthritis syndrome
16. One case of
C. cayetanensis oocysts found in the sputum of 60-year-old HIV negative male with a history of successfully treated TB has been reported in Argentina
49, and a similar case has also been reported in Egypt where a 45 year-old HIV negative male with TB history also presented oocysts in the sputum accompanied with active TB infection
50. The latter has prompted calls for the inclusion of cyclosporiasis as a new causative agent of respiratory disease and as a differential diagnosis for TB. In both TB negative and positive cases, the patients presented with loss of weight, cough with expectoration of purulent sputum and dyspnea. The implications of pulmonary infection to the biology, life cycle and transmission of
C. cayetanensis remains to be evaluated, as does its interaction with TB, a disease currently on the increase in Africa due to the HIV/AIDS pandemic
51.
Treatment
Symptoms resolve with the administration of Trimethoprim-Sulfamethoxazole, the standard treatment for cyclosporiasis at 160/800 mg oral dose taken twice a day for 7 days or 160/800 mg oral dose taken 4 times a day for 10 days in immunocompromised patients with AIDS often with symptoms resolving and passage of oocysts in the stool ceasing within 24–48 hr
52, 53.
Epidemiology in endemic setting
The first epidemiological studies conducted in an area endemic for
C. cayetanensis, were carried out in 1997–1998 in Guatemala where raspberry exports to USA were linked to cyclosporiasis outbreaks
10. Children of age groups 1.5 to 4 years and 5 to 9 years were found to be 5 times more likely to be positive for
C. cayetanensis in stool samples than adults. Overall infection did not differ significantly by sex. The infection rates were also found to fluctuate seasonally, with prevalence peaking in the rainy season (6.7%) and falling to undetectable levels in the dry seasons. Drinking of untreated water or swimming in rivers or springs, having a septic tank as opposed to municipal sewage, direct contact with the soil and ownership of dogs, chicken or other fowls, were all found to significantly increase risk of infection although cats and pigs did not
10.
Subsequent epidemiological studies in endemics areas of Haiti, Nepal and Peru have corroborated higher infection rates in children, seasonal fluctuation of prevalence, and risk associated with water source and ownership of domestic animals, particularly fowl, guinea pigs and rabbits37, 54. However no oocysts were detected in a survey for C. cayetanensis in domestic animals carried out for 1.5 years in an endemic area in Haiti, ruling out domestic animals as a reservoir24. Studies in Peru have also shown that previous infection offers significant protection against subsequent exposures54. This consolation is however short lived as clinical sequale may still be linked with asymptomatic infection. Humans are therefore the only known host for C. cayetanensis, but the eating of raw or insufficiently cooked bivalves, which are filter feeders that concentrate pathogens from waters, has been shown to be a risk factor55.
Reports of Cyclospora spp. infecting non-human primates in the East African countries of Uganda, Kenya, Tanzania and Ethiopia have led to efforts to conduct studies of non-human primates in order to better understand the epidemiology and ecology of endemic cyclosporiasis25, 56–59. Host specificity of Cyclospora species in the different non-human primates, geographic overlaps of both monkey and parasite species notwithstanding, corroborated the likelihood of humans as the sole definitive host of C. cayetanensis58. However the collection of oocyst positive stools from the studied troops of vervet monkeys, baboons and colobus monkeys at all times of the year in Kenya, which is notable for extreme weather patterns, demonstrated a lack of seasonality in infection contrary to expectations58.
Cyclospora the enigma
It is clear that the epidemiology of cyclosporiasis as we know it today is a study in contradictions, as the causative agent itself remains shrouded in mystery. How can a pathogen incapable of direct faecal-oral infection and lacking a zoonotic reservoir or ubiquitous presence in the environment
38, be responsible for so many widespread outbreaks of gastroenteritis all over the world? Trace amounts of oocyst contamination in food products indicate that the infective dose of
C. cayetanensis is likely to be very low
38. However attempts at experimental infection in both humans and animals have all proved futile
25, 60. The lack of an animal model has therefore made it hard to determine the viability of oocyst exposed to varying environment conditions that may impact its transmission
38. While most outbreaks have been linked to food sources, just as many unexplained sporadic cases linked to water/sewage transmission have been reported in the developed countries
32, 38, 61. These cases may signify ubiquitous endemicity, remaining undetected due to seasonality of infection, but by what means the parasite survives from one infection season to the next remains unknown.
Even more puzzling is the dearth of C. cayetanensis reports in African populations and as a cause of traveller's diarrhoea in visitors returning from the continent. The screening of over 4,800 samples using modified acid fast staining, and other concerted efforts in previous years have all failed to determine the presence of C. cayetanensis in Kenya62. In addition to economic restraints for effective routine diagnosis in health centres and national/regional surveillance, it has been postulated that the amount of sulpha drugs administered in sub Saharan Africa as drugs of choice for malaria and other infectious diseases may suppress the parasite, humans being the only reservoir36. Could sulfadoxine-pyrimethamine (SP), the now largely ineffective but still affordable treatment of malaria, be our unlikely saviour? Or is it the use of trimethoprim (Septrin), which is widely used as a first line of antibiotics and in management of HIV before ARVs? Significantly higher HIV and malaria prevalence in sub-Saharan Africa may account for a higher drug pressure than other parts of the world, however, the withdrawal of SP as a first line antimalarial due to resistance and similar use of Septrin in C. cayetanensis endemic Peru and Haiti where 5–11% HIV prevalence have been documented, makes the dearth of reported African cyclosporiasis all the more mysterious.
The controversy and questions surrounding C. cayetanensis are no less intriguing. Whereas there is compelling molecular evidence for its reclassification as a mammalian Eimeria species, only C. cayetanensis DNA sequences and C. colobi, C. cercopitheci and C. papionis from East African non-human primates are available 27, 34, 36, 57. The way forward on the classification of this parasite in the light of these new developments remains uncharted waters. The biology of C. cayetanensis in the host is no less intriguing. The presence of oocysts in HIV negative TB patients strongly suggests the existence of an extra-intestinal parasite lifecycle and colonization in humans that is yet unknown49, 50. Moreover, more studies are required to determine whether C. cayetanensis interacts with TB or has only been observed in TB patients because it is an acid-fast staining organism like the TB bacillum. Extra-intestinal stages in the life cycle of Cyclospora talpae in European moles have been demonstrated in the liver where sexual stages develop in the bile duct epithelial cells63, 64. C. cayetanensis has similarly been shown to cause biliary disease in HIV/AIDS patients suggesting possible colonization of the liver18, 36. Unfortunately, the lack of animal/experimental models remains an impediment to resolving these questions.
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