INTESTINAL (Protozoa) AND LIVER PARASITES
SPOROZOEA Order: Eucoccidiida

CRYPTOSPORIDIUM PARVUM

A Review of Cryptosporidiosis

Omar A. Khan, Associate Faculty, Dept. of International Health,
Johns Hopkins University School  of  Public Health,  Suite 310,
111 Market Place Baltimore, Maryland 21202-4024 USA.

Table of Contents

Introduction - Historical Background & Importance - Modes of Transmission & Outbreak Potential - Epidemiology - Biology & Pathogenesis

Laboratory Aspects - Current Prevention & Control Methods - Future Strategies in Treatment & Prevention - Sources of Information on Cryptosporidiosis

Tables - References

Introduction

By the mid-1950s, infectious diseases appeared to be receding from the U.S..
Today, microbial health threats are once more a source of concern; these diseases are in some cases resurgent, eg. tuberculosis, and some completely new to humans, eg. Cryptosporidiosis.
Much has been made recently of these emerging infections, from Ebola to hantavirus to a new form of cholera.
The reasons for emergence differ by disease, and we focus here on the disease cryptosporidiosis which has recently become a topic of great interest.
There has been sufficient interest in emerging infectious diseases that there is a journal devoted exclusively to the topic; symposia have been held at various academic and research institutes, and programs of study focusing on this field have been created (CDC, 1995).
The emergence of diseases affecting humans is due to many different factors, depending on the particular disease.
It may be due to the expansion of human habitat into the niche of a virulent organism or its vector, as in Lyme disease (National Science & Technology Council, 1995).
It may also be a new strain of an existing microbe, as in drug-resistant forms of influenza and tuberculosis or changes in climate and /or ecology, giving rise to new infections such as the O139 strain of cholera.
A new niche for infection may also be created by environmentally acquired or genetic immune deficiencies on the part of the host.
The epidemic of Acquired Immune Deficiency Syndrome is one such example, which has left us vulnerable to many opportunistic infections.
In this case the main factor contributing to disease emergence is increased host susceptibility and infections formerly harmless or at most acute, self-limiting now pose a serious threat to life.
Cryptosporidiosis is such a disease; it has become a cause for concern mostly due to a predisposing condition (immunosuppression) on the part of its human hosts, mediated by the AIDS epidemic.

Cryptosporidium parvum is the parasitic protozoan that causes human cryptosporidiosis, as well as in certain animals, including domestic livestock.
In humans it causes abdominal pain, profuse diarrhoea, weight loss, loss of appetite and anorexia, but in otherwise healthy individuals the infection is usually self-limiting and resolves within a few weeks (Soave, 1994).
In immunocompromised patients the infection is more serious; it can become chronic and is sometimes fatal. There is no definitive cure for the disease.
These protozoa complete their life cycles in a single host, and their oocysts are highly infectious. These oocysts are usually transmitted by contaminated water, fecal transmission from infected animals, person-to-person spread or contaminated food.
Water treatment plants cannot usually guarantee to remove all C. parvum from water because the oocysts are very small (4-5 micrometers in diameter) and are resistant to chlorine and other disinfectants.
[See Biology & Pathogenesis section for details].
At present, control of water supplies depends on limiting contamination of input water by animals, manure or sewage, and by careful maintenance of water treatment systems.
C. parvum is inactivated by heat, freezing and drying, so heat-treated, frozen and dried foods are considered safe (Blanchfield, 1996).

Historical Background & Importance

Cryptosporidium parvum is a protozoan belonging to the Phylum Apicomplexa, subclass Coccidia, and is related to other medically important coccidia such as Toxoplasma gondii, Isospora belli and Plasmodium species (Goodgame 1996).
The organism was discovered early in the twentieth century, by Tyzzer in 1907, but its importance was only realized in the 1970s by veterinary workers.
In 1976, it was identified at the Johns Hopkins School of Medicine as the causative agent of human cryptosporidiosis (Nime, Burek, Page and Yardley, 1976).
The pathogenic potential of the parasite was not fully appreciated until 1982, when the prevalence figures began to rise, largely as a result of the onset of the AIDS epidemic.
Cryptosporidium parvum is now believed to be an enteric pathogen with a world-wide distribution.
Infection rates are predicted to be highest in developing countries and in children (Black, 1996), but the information available from developing or developed countries outside of the US is either anecdotal or based on assumptions which may be very different form the actual situation.
Surveillance for the disease is a recommended initial step [refer to section on Future Strategies in Prevention].
As such, cryptosporidiosis represents a classic ‘emerging infection’; previously unknown in such severity, it has become important owing to its potential for fatal outcomes in HIV+ individuals.
Since treatments are still in the developmental phase, current control efforts are largely directed at prevention methods.

Modes of Transmission & Outbreak Potential

-Infectivity

The parasite is transmitted by the fecal-oral route and infection may be acquired in a number of ways:
  a) from contaminated water (the source of most of the major recorded outbreaks)
  b) from animals, particularly lambs and calves, through contact with their infected feces;
  c) person to person contact, which is considered especially relevant in child day-care centers;
  d) from contaminated raw foods, e.g. raw meat, unpasteurized milk, fruit and vegetables.

Farmyard manure may contain high numbers of Cryptosporidium oocysts and consequently water may be contaminated by manure or slurry washed off fields into rivers; vegetable crops may be contaminated by direct manuring of the fields in which they are grown.
Well managed and stored manure is effective in reducing infectivity through raised temperature and ammonia levels (Moore et al, 1995).
An essential issue in the infective potential of Cryptosporidium oocysts is their resistance to disinfection and environmental pressures.
Oocysts can remain viable for about 18 months in a cool, damp or wet environment. They are quite common in rivers and lakes, especially where there has been sewage or animal contamination.
Desiccation over a sufficient period of time (2 hours or more) is lethal to the oocysts (Robertson et al, 1992).
They are generally susceptible to freezing temperature as well, although this varies by onset of freezing:snap-freezing destroys oocysts reliably, but with slow freezing, such as that found in the natural environment, oocysts have been reported to survive at temperatures as low as -22 degrees C (Robertson et al, 1992).
They are also heat sensitive; a temperature of 65 degrees C inactivates oocysts in 5-10 minutes.
Cryptosporidium oocysts are remarkably resistant to many common disinfectants, including chlorine-based compounds.
Very high concentrations of disinfectant may be effective, but such levels are not practical for water treatment (Robertson et al, 1992). Some of these disinfectants are listed in Table 1.
The complete removal of C. parvum from water supplies is difficult, even for modern water treatment plants. The oocysts are resistant to the normal chlorine disinfection treatment.
The standard water treatment at many plants involves mechanical flocculation, sedimentation and rapid sand filtration.
This treatment was in use at some of the plants where oocysts did manage to breach the filters (see next section).
Treatment with alum (aluminum sulfate) or lime can be effective, due to the susceptibility of C. parvum to that level of alkalinity. However, in neutralizing the pH in US filtration environments, these treatments lose their value.
In some US filtration plants such as the one implicated in the Milwaukee outbreak, backwash water is used to clean the sand filters. This process results in a high concentration of oocysts in this water; since this contaminated water may be subsequently ‘recycled’ to the beginning of the filtration cycle without intermediate oocyst removal, there is greater chance of C. parvum breakthrough when the water comes back to be filtered (Lisle & Rose, 1995)
Therefore, current practices do not uniformly guarantee the complete removal of these protozoa from water supplies.
In view of this, both English and American public health authorities have recently advised severely immunocompromised people to boil drinking water in order to reduce the chance of acquiring waterborne cryptosporidiosis (Moore et al, 1995)
(See "Current Prevention & Control Method" section for further details).
Commercial bottled water may also be contaminated, and since it is not regulated stringently, is not guaranteed free of C. parvum; it is advisable to bring water to the boil to eliminate infective organisms.
It should be stressed that to be effective the guidance must be followed consistently for all water used for drinking or for washing foods intended for consumption without cooking.
C. parvum does not multiply in food, but oocysts can survive in wet/moist foods if they become contaminated.
Cooked foods are not thought to be at risk and the normal recommended time and temperature for controlling bacterial food poisoning (an internal temperature of 70 deg C for 2 minutes) should inactivate C. parvum; heat processed foods have not been reliably shown to be a source of infection (Blanchfield, 1996).

-Outbreaks

In the U.S. cryptosporidiosis is regarded as having significant outbreak potential.
The largest recognized outbreak was in Milwaukee in 1993 when it was estimated that some 400,000 people may have been affected by contaminated drinking water (see Table 2).
The suspected cause was a deficiency in treatment, possibly contamination of filtered water with raw, untreated water.
Other operational deficiencies were also suspected such as inadequate monitoring of water turbidity and inoperable equipment (Lisle & Rose, 1995).
In the UK there have been several outbreaks associated with farm visits and some well-publicized water-borne outbreaks, the larger ones with over 500 people affected (Meinhardt et al, 1996).
In many of the UK cases, the filtration equipment was either not setup to handle large numbers of oocysts, or was functioning below standards.
The provisional figure for the number of reported cases in England and Wales in 1994 was 4424 but, as many cases are thought to be unreported, the actual number of cases is probably several times higher (Lisle & Rose 1995).
Cryptosporidiosis may show a seasonal distribution and at peaks it may be the commonest enteric pathogen being isolated from children.
In one 2-year study C. parvum was found twice as often in the U.K. as Salmonella spp., in children aged 1 to 5 years (Badenoch, 1990).
Such outbreaks are especially harmful for HIV+ individuals, who may face death in the absence of a cure.
The U.S. has recommended certain universal standards for water authorities and consumers (see ‘Current Prevention & Control Methods’ section).
It is interesting to note that although there were operational deficiencies in the Wisconsin outbreak in 1993, which led to unfiltered water being combined with filtered, the Georgia plant was still functioning within guidelines for filtration, as regards turbidity and disinfection.
It was the extreme resistance of the oocysts which led to the subsequent outbreak, which in turn led to stricter guidelines for purification (NSTC, 1994; Graczyk, pers. comm.).
Standards for water purity in the U.S. have been strengthened by the EPA in response to cryptosporidiosis outbreaks; however, small numbers of oocysts can still theoretically breach filtration in a quarter to half the communities with the strengthened standards (Moore et al, 1995).

Epidemiology

One of the main reasons cryptosporidiosis gained importance was due to the epidemic of HIV/AIDS, which created a pool of susceptible individuals.
Globally, there are close to 24 million individuals either HIV+ or with AIDS.
Proportionally, North America has only 3.7% of these individuals; Sub-Saharan Africa accounts for the greatest number and proportion, with 62% in that region (UNAIDS, 1996).
The proportion of those positive for HIV is growing in regions of South and South-East Asia, making the need for prevention in those regions imperative as well.
In 1996, official estimates put the figure of AIDS deaths worldwide at 1.1 million. North America accounted for a relatively low 61,000 deaths.
Sub-Saharan Africa was the hardest hit, with close to 800,000 deaths (UNAIDS, 1996). Of this number, the proportional mortality due to cryptosporidiosis is unknown.
It should be noted that outside of the ‘developed’ countries, which account for the lowest proportion of HIV-positives, considerable under-reporting as well as inaccurate reporting as to cause of death are likely.
This means that not only may the actual AIDS figures be higher in these countries, but the proportional mortality due to cryptosporidiosis would be underestimated as well.
Most countries in the world share the dubious distinction of having no testing for C. parvum, either routinely or as cause of death when diarrhea is implicated.
Only recently have some individual clinics have been carrying out studies on AIDS patients with cryptosporidiosis (ProMED, 1996).
However, there is a dearth of consistent and large-scale epidemiological data on the disease, even though it has been reported from all six continents, in rural and urban populations (Meinhardt et al, 1996).
Aside from the main group of immunocompromised individuals, infections have been noted in immunocompetent 1-5 year olds as well. (Casemore, 1983).
Other reports also indicate infections in infants (under 12 months of age), particularly in developing countries (Mathan 1985, Cruz 1988).
One meta-analysis reported 24% of immunocompromised patients with diarrhea in developing areas to be suffering from cryptosporidiosis (compared with 14% in developed countries (Martins & Guerrant, 1995) (See Table 3).
Even though there are no other large-scale studies to validate these findings, these figures have important implications in that not only developing but also the so-called developed countries have traditionally low surveillance for cryptosporidiosis, and diarrhea due to C. parvum may be mis-diagnosed as due to more common organisms such as Entamoeba, V. cholerae or Shigella species (Cutting, 1993).
Many animal species can be infected and C. parvum is readily passed from animals to humans. Due to inadequate identification of either specific causes of death or the etiologic agent in cases of diarrheal disease morbidity and mortality, deaths attributed solely to causes such as cholera and shigellosis must be considered dubious in both lesser and more developed countries.
Accurate data are not yet available as to the extent of cryptosporidiosis worldwide, however, estimates are that 3 - 7% of reported diarrheal disease in developing countries is caused by Cryptosporidium species (Black, 1996).
Mean prevalence rates for Asia and Africa are estimated at 4.9% and 10.4%, respectively (Ungar, 1990) in one study as well.
It is worth noting that these estimates, to be found in Medline-indexed journals, do not include any data from surveys, but are based purely on hypotheses.
While they represent a starting point for further research, the figures presented therein should not be considered accurate or representative; this is especially true for figures presented at the continent-level, where significant variations in parasite distribution and host susceptibility reduce the value of these data.
Cryptosporidiosis has also been recognized as a possible cause of "traveler's diarrhoea".
In countries where water supplies are often contaminated, sanitation levels inadequate and close contact with animals, infection rates can be high (Swerdlow & Rees, 1992).
Recent studies indicate that Cryptosporidium oocysts are present in 65-97% of surface water in the U.S. (Blanchfield, 1996).
However, since only C. parvum is infectious to humans, the importance of this figure may be overstated.
No current method can completely guarantee the removal of oocysts, primarily owing to their small size and resistance to disinfection.
However, a method under development at Johns Hopkins (Clive Shiff & Thaddeus Graczyk, pers. comm.) may have commercial applications since it effectively removes oocysts without affecting infectivity.

Biology & Pathogenesis

Numerous reports have described clinical cryptosporidiosis in mammals, reptiles, birds and possibly fish. The symptoms can persist and become fatal in the case of congenital, acquired or therapy-mediated immunosuppression.
The earlier reports assumed that Cryptosporidium species were host-specific, and named the 20-odd species thusly.
However, cross transmission studies demonstrated transmission between different host species, and it was proposed that Cryptosporidium be considered a monotypic genus (Tzipori, Angus, Gray, Campbell and & Allan, 1981).
The current state of affairs regarding the specificity within classes of Cryptosporidium species is under debate; most studies however confirm that separate species exist in different vertebrate classes.
Further characterization studies need to be conducted to define the epizootology of the organism.
To date, a total of 21 species of Cryptosporidium have been identified (for main species, see Table 4) (O’Donoghue, 1995).
However, not all species are considered valid; some of the earlier isolates are now under scrutiny and the validity of some others has been questioned due to recent results of cross-transmission studies (Levine, 1986).

-Life Cycle

Cryptosporidium has a complex, homoxenous life cycle, i.e. it is able to complete its cycle in a single host.

Unlike other coccidian species, an external period is not required for sporulation. Consequently, oocysts are excreted from the gut in infective form, with potential for direct fecal-oral transmission.

The characteristic stages of Cryptosporidium are excystment, asexual budding (schizogony/ merogony), sexual multiplication (gamogony), zygote and oocyst formation, and sporogony.
Mature oocysts contain 4 sporozooites. The oocysts ‘excyst’ to liberate sporozooites in the gastrointestinal tract.
Excystation is possibly triggered by a combination of environmental conditions such as pH, bile salts, carbon dioxide and temperature (Fayer & Leek, 1984).
The free sporozooites attach to epithelial cells and at this point are referred to sometimes as trophozooites.

These are 2-6 microns in diameter, and in histological sections give the brush border of the cell a granular appearance.

Electron microscopy has confirmed their intracellular, extracytoplasmic location within vacuoles (Gobel & Brandler, 1982).
The parasites contain a unique ‘feeder’ structure at the base of each vacuole. This organelle is thought to mediate nutrient uptake from the cell (Current & Reese, 1986).

The trophozooites then undergo asexual reproduction to form merozooites.
Sexual reproduction occurs by the subsequent development of male and female gamonts, which develop into gametocytes.
Following fertilization these give rise to zygotes which undergo further asexual development, producing oocysts containing four sporozooites (O’Donoghue, 1995).
These oocysts may now be excreted or begin a new cycle within the host. They do not need any further maturation, unlike many other Coccidian protozoa.
Excretion may stop fairly promptly after the cessation of diarrhoea or it may continue at low levels for some weeks even after all symptoms of illness have gone.
An incubation period of 2-14 days follows ingestion of oocysts. Very low doses are able to initiate an infection, probably less than 100 oocysts. The illness is characterized by a profuse watery diarrhoea with abdominal pain.
It can also cause vomiting, weight loss, loss of appetite and a low grade fever. Typically the illness resolves in 2-3 weeks but it can last for up to 6 weeks (Soave, 1990).
It should be noted that infective dose of the parasite is extremely low, and they are very resistant to disinfection. Under natural conditions of varying temperature and various environmental pressures the oocysts are hardy as well.
Their small size, buoyancy and ability to remain dormant allows them to escape most natural hazards. Only supportive treatment (e.g. ORT) is available, and this will only be required in serious cases.
However, in severely immunocompromised patients, e.g. AIDS sufferers, the infection may become chronic and serious, sometimes fatal.
In these cases other organs and tissues may become infected, e.g. the biliary tract and respiratory system.

Laboratory Aspects

A variety of tests such as Enzyme Immuno Assay (EIA) and Immuno Fluorescent Antibody (IFA) (both direct and indirect methods) can detect Cryptosporidium, although they are not particularly specific when required to distinguish between C. parvum and non-C. parvum.
This is an important and desirable feature in differential testing, since only C. parvum is known to cause cryptosporidiosis in humans.
EIA has been experimentally shown to be more specific than the IFA tests, i.e. better at detecting C. parvum while excluding non-C. parvum species,but all the reviewed commercially available diagnostic tests will give a positive result for non-C. parvum species (Graczyk & Cranfield, 1996).
This points to the need for better diagnostics to reliably determine C. parvum presence in suspect substances. (See Table 5 for comparison of test methods).
Polymerase Chain Reaction (PCR) is one of the few ways to distinguish accurately between C. parvum and non-C. parvum.
Mouse monoclonal antibodies have also been used to detect oocysts in fecal and water samples by immunofluorescence (Sterling & Arrowood, 1986).

Most infections are diagnosed in the laboratory on the basis of acid-fast or immunofluorescence (IFA) staining of oocysts in fecal smears (Guerrant, 1997).
Concentration methods may enhance detection of low numbers of oocysts, but from the literature reviewed it appears that there may be some loss of occysts during the concentration procedure.
Acid-fast staining is the laboratory stain in greatest use, but negative staining has been shown in some cases more efficacious (Ma & Soave, 1983).
ELISA methods are used for diagnosis as well, but with variable sensitivity (83-95%), IFA would seem to be a better choice.
Recently, PCR methods are being used as well for C. parvum DNA detection in fixed tissue (Laxer, 1992; Guerrant, 1997).
This method has the advantage of accurately distinguishing C. parvum from non-C. parvum species.

-Genetics

Studies on the genetics of Cryptosporidium spp. are ongoing. DNA and isoenzyme characterization studies have shown significant genotypic differences between isolates.
Pulsed-field electrophoretic studies have resolved 5-6 chromosomes for C. parvum isolates, although additional ones may be present as well.
Chromosome size has not been well-characterized; sizes ranging from 900 to 3300 kb (depending on the technique employed) have been obtained.
No difference was found in the chromosomal banding patterns of C. parvum isolates from humans, calves or horses.
Significant differences were observed between C. parvum and C. baileyi isolates (Laxer et al, 1992).
Most studies have detected significant molecular variation between Cryptosporidium species, as well as in different isolates of the same species.
The genetic basis of this variation needs to be characterized, with respect to virulence characteristics, immunogenicity and drug susceptibility.
Several studies have identified recombinant or partial fusion antigens.
These include a sporozooite protein of 140 000 mol. wt., a large sporozooite and merozooite glycoprotein (300 000 mol. wt.), another large sporozooite glycoprotein (900 000 mol. wt.) encoded by a single copy gene on the largest chromosome, an oocyst wall protein (190 000 mol. wt.) and an epitope shared by two recombinant proteins (15 000 and 60 000 mol. wt.).
Other genes identified include a potential ATPase, a structural protein, a DNA-binding protein, and various cytoskeletal proteins (Current & Garcia, 1991).

-Filtration studies at Hopkins

This section is included to provide a brief overview of some of the work relating to Cryptosporidium testing at Johns Hopkins.
The aim of these experiments was to ascertain whether oocyst viability was affected by the method of filtration and processing.
This is important since it indicates the ‘transparency’ of the filtration method, ie whether the oocysts recovered after filtration are more or less viable than those found in the environment.
The equipment used for filtration of the oocysts was the Millipore apparatus, fitted with a vacuum pump and a Cellulose Acetate Membrane (CAM) of pore width averaging 1.2 micrometers.
As pointed out earlier, C. parvum oocysts are of roughly 5 micrometer width.
The test solution containing oocysts was filtered through the CAM, following which the CAM was processed with acetone.
This dissolves the membrane, leaving behind, ideally, membrane-free oocysts which are recovered in a pellet following centrifugation.
The acetone solution was centrifuged three times at 12,000 RPMs at 4 degrees C.
The acetone was then removed almost completely, leaving just enough to protect against oocysts drying out and possibly losing viability.
The pellet formed by the procedure was successively washed and centrifuged with 95% alcohol, 75% alcohol and finally water.
The resulting test oocyst solution from the pellet was excysted using a bile salt solution (incubated for 30 minutes at 37 C), in comparison with a control solution of oocysts.
The Excystation Index (EI) was determined by the ratio of sporozooites to intact oocysts, observed under a light microscope, by observation of ten fields or ten minutes.
The results from this study are shown in Table 6.
The mean EI observed for the test group versus the control was similar; in no instance did the control EI exceed the test EI; these results tentatively establish that the laboratory procedure evaluated in this study does not negatively affect waterborne C. parvum oocyst viability.
Procedures for filtration vary, but a procedure in use at filtration plants involves the addition of disinfectant, mixing, flocculation (to cause ’clumping’ of solids), sedimentation and rapid sand filtration.
The above procedure is unique in that it utilizes a membrane filter. It may be noted that the manufacturer of the 1.2 micron CAM used in this laboratory also makes a large version for large-scale industrial applications.
This has implications for widespread application of this method in the future, toward developing a transparent filtration/recovery system.

Current Prevention & Control Methods

All cryptosporidiosis infections are caused by ingestion/inhalation of oocysts. Therefore, prevention measures must aim to limit host contact with the organism. 
Current measures focus on hygiene, as for most diarrhea-causing agents (enteropathogens).  Disease outbreaks can be prevented by implementing the following recommendations.

a) Instituting stringent standards for water purification and filtration. In laboratory tests, filters with pores of diameter 1 - 2 micrometers are effective at straining the small, 4-5 micrometer oocysts. 
Utilization of such a commercial filter by local water authorities should prove effective. Cost is as yet undetermined since there is no published record of the use of the small-pore filters. 
However, with widespread use, in response to a growing need, the cost increase should be minimal, as well as justifiable.

b) Routine testing of purified and unpurified water to check for the presence of Cryptosporidium parvum  oocysts.
Commercially available Enzyme ImmunoAssay (EIA) kits such as ProSPECT Rapid Assay have been shown to be superior to ImmunoFluoresecnt Antibody (IFA) kits such as MERFLUOR (Graczyk & Cranfield, 1996).
However, further evaluation of these EIA kits is necessary to establish which can accurately and consistently test positive for only those Cryptosporidium oocyst of human infective potential (i.e. only Cryptosporidium parvum).

c) Boiling water intended for consumption. Freezing temperatures are not adequate for assuring oocyst elimination.

d) Although commercial bottled water is not guaranteed free of oocysts, it still represents an improvement over tap water, especially during travel to areas with inadequate or unreliable drinking water facilities.This includes developing countries as well as developed.

e) Using a home microstraining water filter, capable of removing particles 1 micrometer in size. They should be labeled as ‘Absolute’, and meeting American Water Works Association (AWWA) and standards for ‘Cyst Removal’ (Roberson, 1997).
Since bacterial overgrowth on such filters can be a supplementary health hazard, the cartridge should be changed according to the recommend intervals.
In addition, the CDC recommends for immunocompromised patients to wear gloves while changing the cartridge or ask another person to change it (NSTC, 1995).

f) Information dissemination through print media to educate the public regarding the dangers of cryptosporidiosis, and effective preventive means.
The CDC and many state and local health authorities have begun such efforts already (NSTC, 1995). Such interventions can be useful if carried out with appropriate formative research.

Future Strategies in Treatment & Prevention

Although no antibiotic treatment has yet been shown to be effective in clinical use, some encouraging results following use of paromomycin (an aminoglycoside antibiotic) have been reported.
There is also preliminary evidence to suggest that paromycin when used at 4 doses of 1.5 -2.0g/day has led to symptom improvement, and even eradication of the parasite.
However, doses required to produce this effect in all patients would approach toxicity. Although Azithromycin and Lactobin-R (bovine colostrum immunoglobulin concentrate) have had some experimental success, no therapeutic agent has been clearly identified as effective (Martins & Guerrant, 1994).

-Prevention Possibilities:

As there are currently no reliable curative therapies for cryptosporidiosis, the best hope lies in prevention of disease outbreaks. Some examples of measures I consider pertinent are as follows.

-GIS Surveillance

Geographic Information Systems, or GIS, present a new and effective method for surveillance of infectious disease. A GIS consists of a database with geographically-correlated data points, connected to a functional map.
A GIS allows for data input and is capable of storing, manipulating and displaying these data regarding the location, conditions and patterns of the relevant variable.
Color variation and shading schemes can be used to distinguish the various data types.
One of the major advantages of GIS over conventional maps or even acetate overlays is the ability to juxtapose data; to superimpose the variables of choice, to observe any emergent relationships and to analyze them, all using a computer.
For cryptosporidiosis control, GIS is currently in use in North Carolina, by the state health and veterinary medicine departments (McGinn et al, 1996).
Farm locations which are a potential source of Cryptosporidium oocysts, can be mapped against water sources such as rivers and reservoirs.
Combining these with topographic data can yield information on the amount of Cryptosporidium contamination that could be expected due to runoff.
This has obvious advantages when planning or approving cattle farm sites and drinking water sources, as well as help to localize possible sources of an outbreak.
Possible preventive applications of GIS can be maximized by connecting the database to a ‘real time’ remote sensing system.
‘Real time’ means that data are stored in the GIS database as soon as or soon after they are generated by the remote sensing system, such a satellite mounted GPS (Geographical Positioning System).
The GPS can provide instantaneous updates, or at discrete time intervals, regarding the change in relevant variables, such as the construction of new houses near cattle farms, the movement of animal herds and the progress of a disease outbreak.
Such a system has been used for tracking and preventing cholera outbreaks in Bangladesh, where the main research center for disease, the International Centre for Diarrheal Disease Research, Bangladesh (ICDDR,B), has set up a GIS connected to a remote sensing GPS (Myaux, 1997).
This enables the center to track environmental indicators that signal a possible outbreak, to monitor case progression, and to enact preventive therapies and education campaigns in anticipation.
For example, using an indicator such as algal blooms (a putative reservoir for vibrio cholerae) in the Bay of of Bengal, their pattern of drift can be correlated with subsequent outbreaks of cholera.
Using this as a predictive tool, health facilities can be forewarned of impending outbreaks and measures to redice the severity of the outbreak can be enacted.

- Information, Education & Communication (IEC) campaigns

Using Information, Education & Communication (IEC) campaigns is one effective means to get across the message with relatively low cost (Myaux, 1997).
IEC messages can be broadcast, advertisement-style, over mass media channels such as television and radio, and in more developed areas, the Internet.
An example is the PROMed system for monitoring outbreaks, for which one needs a computer to connect, and then receive timely updates regarding emerging infectious disease from around the world.
One may subscribe to the service via a ‘listserv’ (an Internet discussion group) which connects the incoming messages and allows posting of messages from one’s electronic mail account.
Such a system allows all subscribers to benefit from the surveillance results and technological capacity of others.

Sources of Information on Cryptosporidiosis

Table 1:
Common disinfectants against Cryptosporidium species

O’Donoghue, 1995

Table 2:
The largest confirmed outbreaks

5900

2006

12,960

12 960

24,000

27

741,092

516

551

551

177, 300

47

15,000

15,000

403,000

403,000

Lisle & Rose, 1995

Table 3:
Results of study of diarrhea patients in developing and developed countries for cryptosporidiosis

Table 4:
Currently identified species

O’Donoghue, 1995

Table 5:
Comparison of testing methods for Cryptosporidium oocysts

No. Positive

Graczyk & Cranfield, 1996

Table 6:
Trials to determine the comparative Excystation Index

Mean EI

Test Solution

Control

Individual readings

Mean

Individual readings

Mean

Shiff, Graczyk & Khan

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