Before we analyse the associated investigation, let us look at the parasite itself :
Cyclospora was first recognized in the early 1980s in patients with enteric disease. 'Enteric disease' is an elegant medical term that encompasses the whole spectrum of clinical signs (nausea, diarrhea, abdominal pain, cramps etc) that are manifested by pathological changes in the small and large intestines. Cyclospora was initially misdiagnosed as everything ranging from artifacts to blue green alga, with the range in between including Cryptosporidium, Isospora, Coccidian-like body, cyanobacterium-like body, and unidentified flagellate. Reports in 1995 put an end to speculation by characterizing the SSU rRNA gene and concluding that the parasite was related to Eimeria , which as you all know is a Coccidian apicomplexan.
Cyclospora sps. are parasites of a wide range of snakes, rodents and mammals, not necessarily in that order, and they appear to be monoxenic (that is to say, they complete all parts of their lifecycle in one host). As is tradition, the oocysts are of diagnostic importance and are fairly typical. They have two sporocysts with two sporozoites each. Each of the sporozoites is folded in two. Diagnostic tests that detect the parasite are in fact designed to recognize this stage. These include the classic ones including the acid fast staining (picture below) with bright field microscopy, modified safranin staining, trichrome staining and the unconventional UV epifluorescence microscopy. Jejunal biopsies and PCR amplification of target genes can detect other stages besides the oocyst stage, which is shown below.
(Source : http://phil.cdc.gov/Phil/details.asp )
A typical Coccidian life cycle
Oocysts are excreted unsporulated in the feces of the infected host. They sporulate in 7 -15 days and become infectious. The sporulated oocysts ultimately come to be found on the surfaces of green leafy vegetables and fruits. Upon ingestion by a new host, the oocysts excyst, infect the columnar epithelial cells of the proximal intestines (viz, duodenum and jejunum) and undergo merogony to produce two types of meronts that differentiate and undergo gametogony. The macro and microgametocytes fuse to form oocysts that are excreted.
Public health concerns
Evaluating the parasite from the perspective of the epidemiological triad brings out the following:
Parasite factors : Long sporulation time (7-15 days), which precludes direct person-to-person transmission; resistance to common disinfectants including chlorine; surface adhesins confer strong attachment to fresh produce.
Host factors : So far, Cyclospora cayetanensis seems to infect only humans, although oocysts have been isolated in fowl and dogs in endemic countries. But, the exact role of intermediate and transport hosts is yet to be elucidated, as is also the role of Cyclospora as an opportunistic pathogen. Undoubtedly, infections in immunocompromised patients are symptomatic, especially when the immunocompromise is due to infection with that devious Lentivirus called the Human Immunodeficiency Virus. A 2003 study in Venezuela reported a high percentage of asymptomatic carriers among the other major target population viz. infants.
Animal models have been unsuccessful so far.
Environmental factors : Microenvironmental factors that dictate sporulation are not entirely unknown. Temperature between 22C and 32C is needed for sporulation, which confines the circum-annual distribution to the tropics. This also means that the hemisphere experiencing summer at any given time is more prone to outbreaks than its antipodes. Exact seasonality and geographical distribution are under study. This predominantly tropical disease, has led to outbreaks in temperate regions as well due to the importation of fresh produce. Travelers to endemic areas tend to pick up the infection due to sheer lack of knowledge of the existence of a parasite of this sort. A broad knowledge base and smart travel skills have become more important than ever. Cases in the United States are sporadic, of which some are acquired internationally and others domestically.
The map below shows cases that were acquired domestically between 1997 and 2008 :
(Source : cdc.gov/mmwr/preview/mmwrhtml/ss6002a1.htm)
The 2013 outbreak
The summer 2013 outbreak peaked between the 16th and 22th of June, and the second spike occurred between the 30th of June and the 6th of July, with 174 and 111 cases respectively.The five-year incidence mean for the same two weeks are 6.8 and 5.6 cases respectively.
The FDA conducted an Environmental Assessment as part of the response to the outbreak. Investigations were conducted between the 12th and the 19th Aug, 2013, more than five weeks after the last date that patients had eaten at one of the restaurants affected ( i.e. July 2, 2013). (Read the FDA report to obtain restaurant names). The salad mix supplied to the two restaurants was produced by T Farms, in a neighboring country. The salad had contained iceberg lettuce, romaine lettuce, green leaf, red cabbage and carrots, of which only the latter was processed at a different facility.
The processing facility was first investigated in true Sherlock style. Construction and design of the plant,
water processing system, sanitary water system, receipt of raw ingredients, employee health and distribution systems were assessed. These were considered potential sources of the parasite. Infrastructural items and washwater obtained after vegetable washing were systematically cleared and proven negative by standard lab techniques (microscopy and PCR) as the source of the infection.
The source of raw ingredients were assessed in the "ranches" on which they were grown. A thorough examination of the employees working on these ranches and their medical records proved that they were not the source of infection. An assessment of the wells and farms in the vicinity of the ranches proved that they were not sources of infection either. Topography of the land and the rainfall patterns indicated that those geological/meteorological entities did not contribute to the outbreak. The EA team deemed other things on the ranches to be fairly in order and suggested a few minor modifications to the irrigation systems, such as the installation of back flow pumps to wells and the changing of valves on sinks that could potentially lead to cross-contamination.
The final conclusion offered is, " the FDA has not been able to definitively determine how or at what point in the supply chain Cyclospora cayetanensis contaminated the salad mix associated with the outbreak."
Before you criticize or condemn the lack of an expected conclusion, remember that epidemiological investigations are not easy. They do not always conclude successfully. That is, what you want to find is not what you will find. This is true of the biological sciences in general. Hypotheses have to be assessed and changed as one proceeds with data collection. To steadfastly hold onto a pretentious hypothesis and to try and fit the data to your hypothesis is obviously the hallmark of one working with a closed mind. As for Cyclospora, the matter rests for now, atleast until the next food associated outbreak.
References :
Environmental Assessment: 2013 Cyclosporiasis outbreak in Iowa and Nebraska – Findings and Recommendations
http://www.fda.gov/Food/RecallsOutbreaksEmergencies/Outbreaks/ucm375732.htm
Cyclospora sps. are parasites of a wide range of snakes, rodents and mammals, not necessarily in that order, and they appear to be monoxenic (that is to say, they complete all parts of their lifecycle in one host). As is tradition, the oocysts are of diagnostic importance and are fairly typical. They have two sporocysts with two sporozoites each. Each of the sporozoites is folded in two. Diagnostic tests that detect the parasite are in fact designed to recognize this stage. These include the classic ones including the acid fast staining (picture below) with bright field microscopy, modified safranin staining, trichrome staining and the unconventional UV epifluorescence microscopy. Jejunal biopsies and PCR amplification of target genes can detect other stages besides the oocyst stage, which is shown below.
(Source : http://phil.cdc.gov/Phil/details.asp )
A typical Coccidian life cycle
Oocysts are excreted unsporulated in the feces of the infected host. They sporulate in 7 -15 days and become infectious. The sporulated oocysts ultimately come to be found on the surfaces of green leafy vegetables and fruits. Upon ingestion by a new host, the oocysts excyst, infect the columnar epithelial cells of the proximal intestines (viz, duodenum and jejunum) and undergo merogony to produce two types of meronts that differentiate and undergo gametogony. The macro and microgametocytes fuse to form oocysts that are excreted.
(Source : http://www.cdc.gov/parasites/cyclosporiasis/biology.html)
Public health concerns
Evaluating the parasite from the perspective of the epidemiological triad brings out the following:
Parasite factors : Long sporulation time (7-15 days), which precludes direct person-to-person transmission; resistance to common disinfectants including chlorine; surface adhesins confer strong attachment to fresh produce.
Host factors : So far, Cyclospora cayetanensis seems to infect only humans, although oocysts have been isolated in fowl and dogs in endemic countries. But, the exact role of intermediate and transport hosts is yet to be elucidated, as is also the role of Cyclospora as an opportunistic pathogen. Undoubtedly, infections in immunocompromised patients are symptomatic, especially when the immunocompromise is due to infection with that devious Lentivirus called the Human Immunodeficiency Virus. A 2003 study in Venezuela reported a high percentage of asymptomatic carriers among the other major target population viz. infants.
Animal models have been unsuccessful so far.
Environmental factors : Microenvironmental factors that dictate sporulation are not entirely unknown. Temperature between 22C and 32C is needed for sporulation, which confines the circum-annual distribution to the tropics. This also means that the hemisphere experiencing summer at any given time is more prone to outbreaks than its antipodes. Exact seasonality and geographical distribution are under study. This predominantly tropical disease, has led to outbreaks in temperate regions as well due to the importation of fresh produce. Travelers to endemic areas tend to pick up the infection due to sheer lack of knowledge of the existence of a parasite of this sort. A broad knowledge base and smart travel skills have become more important than ever. Cases in the United States are sporadic, of which some are acquired internationally and others domestically.
The map below shows cases that were acquired domestically between 1997 and 2008 :
(Source : cdc.gov/mmwr/preview/mmwrhtml/ss6002a1.htm)
The 2013 outbreak
The summer 2013 outbreak peaked between the 16th and 22th of June, and the second spike occurred between the 30th of June and the 6th of July, with 174 and 111 cases respectively.The five-year incidence mean for the same two weeks are 6.8 and 5.6 cases respectively.
The FDA conducted an Environmental Assessment as part of the response to the outbreak. Investigations were conducted between the 12th and the 19th Aug, 2013, more than five weeks after the last date that patients had eaten at one of the restaurants affected ( i.e. July 2, 2013). (Read the FDA report to obtain restaurant names). The salad mix supplied to the two restaurants was produced by T Farms, in a neighboring country. The salad had contained iceberg lettuce, romaine lettuce, green leaf, red cabbage and carrots, of which only the latter was processed at a different facility.
The processing facility was first investigated in true Sherlock style. Construction and design of the plant,
water processing system, sanitary water system, receipt of raw ingredients, employee health and distribution systems were assessed. These were considered potential sources of the parasite. Infrastructural items and washwater obtained after vegetable washing were systematically cleared and proven negative by standard lab techniques (microscopy and PCR) as the source of the infection.
The source of raw ingredients were assessed in the "ranches" on which they were grown. A thorough examination of the employees working on these ranches and their medical records proved that they were not the source of infection. An assessment of the wells and farms in the vicinity of the ranches proved that they were not sources of infection either. Topography of the land and the rainfall patterns indicated that those geological/meteorological entities did not contribute to the outbreak. The EA team deemed other things on the ranches to be fairly in order and suggested a few minor modifications to the irrigation systems, such as the installation of back flow pumps to wells and the changing of valves on sinks that could potentially lead to cross-contamination.
The final conclusion offered is, " the FDA has not been able to definitively determine how or at what point in the supply chain Cyclospora cayetanensis contaminated the salad mix associated with the outbreak."
Before you criticize or condemn the lack of an expected conclusion, remember that epidemiological investigations are not easy. They do not always conclude successfully. That is, what you want to find is not what you will find. This is true of the biological sciences in general. Hypotheses have to be assessed and changed as one proceeds with data collection. To steadfastly hold onto a pretentious hypothesis and to try and fit the data to your hypothesis is obviously the hallmark of one working with a closed mind. As for Cyclospora, the matter rests for now, atleast until the next food associated outbreak.
References :
Environmental Assessment: 2013 Cyclosporiasis outbreak in Iowa and Nebraska – Findings and Recommendations
http://www.fda.gov/Food/RecallsOutbreaksEmergencies/Outbreaks/ucm375732.htm
