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International Journal of Environment Science and Technology
Center for Environment and Energy Research and Studies (CEERS)
ISSN: 1735-1472 EISSN: 1735-2630
Vol. 4, Num. 2, 2007, pp. 223-232

International Journal of Enviornmental Science and Technology, Vol. 4, No. 2, Spring 2007, pp.223-232

Enumeration of Cryptosporidium spp and Giardia spp (oo)cysts in a tropical eutrophic lake: The municipal lake of Yaounde

1*G. Ajeagah, 1T. Njine, 1S. Foto, 1C. F. Bilong Bilong, 2P. Karanis

1General Biology Laboratory, Faculty of Science, P. O. Box 812, University of Yaounde 1, Cameroon
2National Research Center for Protozoan Diseases, Obihiro University for Agriculture and Veterinary Medicine, Japan
*Corresponding author, Email: ajeagah1@yahoo.fr Tel./Fax: +237 591 657

Received 26 December 2006;
Revised 30 February 2007;
Accepted 10 March 2007;
Available online 20 March 2007

Code Number: st07029

ABSTRACT: The biodynamic of Cryptosporidium spp. oocysts and Giadia spp. cysts have been assessed in the municipal lake of Yaounde, which is an artificial eutrophic lake that has been constructed on the Mingoa stream of the Mfoundi River Basin of Cameroon. The oocysts were identified by the Ziehl-Neelsen method while the cysts were identified by the Lugol iodine coloration. The values obtained suggest an increase in (oo)cysts density from the surface to the bottom of the lentic ecosystem. The oocysts varied from 56 oocysts/L in the upper layer to 2640 oocysts/L of water in the lowest layer, while the cysts population dynamics ranged from 24 cysts/L at the surface layer of the lake to 1713 cysts/L at the lowest layers of the lake. There was a considerable reduction in the resistant forms of these emerging pathogenic protozoa between the surface water of the Mingoa stream entering the Lake and that coming out from the Lake. The highest value of Cyptosporidium oocysts determined at the entrance of the lake is 1480 oocysts/L while at the outlet the highest value of oocysts identified is 620 oocysts/L. The highest value of Giardia cysts determined at the entrance of the lake is 352 cysts/L while at the outlet the highest value recorded is 294 cysts/L.

Key words: Cryptosporidium, oocysts, Giardia, cysts, municipal lake, Yaounde, Cameroon

INTRODUCTION

Cryptosporidium spp. oocysts and Giardia spp. cysts have been reported to be ubiquitous in surface water (Leclerc et al., 2002). Field surveys have also revealed the presence of low levels of oocysts and cysts in underground water (Watanabe et al., 2005). This brings into the light the importance of microbiological and parasitological criteria for the quality control of recycled water that is being made available for potable water production and recreational usage (Katz et al., 2006). In highly industrialized countries the most common human pathogenic protozoa transmitted by water belong to the genera Giardia and Cryptosporidium (Nygard et al., 2006). Parasitic forms are transmitted by the faecal-oral pathway, with food and water being the passive career of the cysts and oocysts (Spinelli et al., 2006). Giardiasis and Cryptosporidiosis are also common infections of domestic and wild animals which shed a relatively large number of cysts and oocysts in the environment (Gomez-Couzo et al. 2005). These resistant forms of the protozoa are insensitive to disinfectants at the concentration commonly discharged in water treatment plants to reduce the pathogenic contamination of drinking water systems, even though it has been observed that at a higher concentration of chlorine and ozone, the cysts of Giardia spp. are less resistant than the oocysts of Cryptosporidium spp. (Finch et al., 2002). Giardia cysts have been shown to survive in water for up to 2 months at temperatures as low as 8 °C, while Cryptosporidium oocysts can survive for up to one year at 4 °C in artificial sea water (Graczyk et al. 2006, Nasser et al. 2006).Alarge number of waterborne outbreaks with both protozoan have been reported worldwide (Karanis et al. ,2006). Giardiasis is a gastrointestinal illness that is being caused by the flagellated protozoan Giardia intestinalis (G. lamblia or G. duodenalis). Some of the symptoms last for a long time. The infection rate for giardiasis is predicted as highest in developing countries (Ford 2006). This disease is highly correlated to the Human Immune Virus (HIV), which is at the origin of the immune deficiency of the human hosts, and thus the cause of an increase in the prevalence of this parasite (Guk et al., 2005).

The clinical symptoms of cryptosporidiosis are a watery diarrhea, abdominal pain, cramps, nausea and weight loss (Gatei, et al., 2006). This disease has gained a high prevalence in recent times because of the immunodepression of their host as a result of the HIV infection (Jong-Kyu, et al., 2005). It is a remarkable zoonotic pathogen, because it infects man and other ver tebrates (Giangaspero, 2006). Cryptosporidium has been reported in rural and urban populations of the six continents. There is an increase risk of infection with this protozoon for persons who are exposed to surface water (Coupe, et al., 2006).

There have been a lot of studies on the biodynamic of the resistant forms of these emerging pathogens in water (Ajeagah, et al., 2005, Smith and Thompson, 2001). Most of these analyses have been carried out on streams. The quantitative data on the identification of oocysts and cysts in lake ecosystems and their survival in a lentic environment is still unavailable in developing countries in general and Cameroon in particular. This hydrosystem could be considered as a significant reservoir of (oo)cysts, that may be resuspended in the water column and give rise to sporadic increases in the oocysts and cysts concentration in the whole river basin in which is situated the lake, resulting in the outbreaks of giardiasis and cryptosporidiosis. The aim of the present research was to evaluate the Giardia spp. cysts and Cryptosporidium spp. oocysts in a tropical ecosystem, which is the municipal lake of Yaounde (Cameroon).

MATERIALS AND METHODS

This study has been carried out in the Yaounde municipal lake which is a eutrophic aquatic ecosystem that is positioned in a NW-SE direction. It results from a dam that has been constructed on one of the tributaries of the Mfoundi River Basin, known as the Mingoa stream. The total surface area of the lake is 7.95X104 m2; it has an estimated volume of 19.104 m3 and a maximum depth of 4.3 m, while the mean depth is 2.4 m as presented on the bathymetry scale. (Fig. 1).

The climate of Yaounde is equatorial, hot and humid, it is characterised by moderate precipitations (annual pluviometry mean of 1576 mm) and temperature has a low mean variation with time(Suchel, 1987). The highest daily mensual thermic amplitude which is 10.4°C is recorded in February, while the lowest value which is 7.2°C is recorded in the month of July. December, January, July and August are the sub arid months, while April, May, September and October are the months with highest rainfall. There exist four seasons which are a long dry season from mid November to mid March, a short rainy season from Mid March to June, a short dry season from July to mid August and a long rainy season from mid August to mid November. The following study was carried from February 2002 to November 2003.

Five sampling points were chosen, which are two points on the Mingoa stream at the Inlet and the Outlet. Three points were selected inside the lake at 0 m of depth, 1 m of depth and 2 m of depth. Ten liters of water were collected from each of the points, at the0 m, 1 m depth and 2 mdepth.A Van dorn bottle of 6 liters of volume was used in the sampling of water for subsequent analysis. The samples were transported to the General Biology Laboratory of the University of Yaounde, where biological and physico-chemical analysis were carried out for the isolation and identifification of Cryptosporidium spp., the water was allowed to settle for 24 hours in the laboratory.

Zinc sulphate solution was added to the concentrated sample and then centrifuged.The supernatant was then concentrated in tubes in the presence of distilled water after a process of centrifugation. The slides were prepared with the deposit.

The oocysts were then fixed with methanol and then coloured with basic fuchsine. The slides were rinced with dilute sulphuric acid and counter coloured with malachite green solution. Cryptosporidium spp. oocysts were then observed and enumerated under the Olympus light microscope at the 400x and 1000x magnification. Giardia cysts were detected from the water by a concentration of particles contained in a 10 L sample. The samples were collected weekly from the sample points. The samples were allowed to settle in the laboratory. The deposit was distributed into centrifuge tubes and then fixed with formaldehyde. The samples were then centrifuged and zinc sulphate was added to the tubes to ensure a re-suspension of the Giardia cysts for eventual coloration with a solution of Lugol iodine. The cysts were observed under the Olympus microscope at the 400x and 1000x magnification. The ammonium nitrogen was analysed by the Nessler method, turbidity and suspended solids were assessed by a direct reading of the water sample on the spectrophotometer.

Table 1: Values of suspended solids (mg/L) in the Mingoa stream and the municipal lake

 

Month/Points Mingoa 1 (inlet) Lake 1(0 m) Lake 2 (1 m) Lake 3 (2 m) Mingoa 2 (Outlet)
February 125 40 60 85 40
March 1500 50 54 237.5 125
April 100 37.5 100 137.5 87.5
May 75 262.5 325 337.5 312.5
June 180 137.5 325 350 360
July 137.5 319 348 387 222
August 121 317 320 337 211
September 125 115 150 200 50
October 300 113 120 172 68
November 325 119 125 198 114

Table 2: Values of turbidity (FTU) in the Mingoa stream and the municipal lake

Month/Points Mingoa 1 (inlet) Lake 1 (0 m) Lake 2 (1 m) Lake 3 (2 m) Mingoa 2 (Outlet)
February 1550 55 70 120 106
March 150 50 175 275 175
April 120 50 100 150 75
May 87.5 50 106.5 125 112.5
June 189 130 150 175 112.5
July 125 87.5 150 637.5 150
August 110 118 120 185 40
September 150 120 130 190 45
October 430 113 117 179 110
November 435 119 140 198 114

 

RESULTS

Cryptosporidium spp. oocysts and Giardia spp. cysts have been isolated and identified in the municipal lake of Yaounde. The oocysts are round in structure (Fig. 7) with a double wall with dimensions ranging from 4-6 micrometers while the cysts (Fig. 6) are oval in structure with the presence of an axostyle, and dimensions ranging from 7-12 micrometers. The results obtained indicate the values for Cryptosporidium oocysts, Giardia cysts and the physico-chemical variables assessed. There is a higher concentration of Cryptosporidium oocysts at the inlet of the lake, with respect to the outlet. The number of oocysts counted increase with the depth. The values of Cryptosporidium oocysts identified range from 205 oocysts/L to 1480 oocysts/ L in the month of August and February respectively. At the outlet of the lake (Mingoa 2), the values range from 40 to 495 oocysts/liter in the months of July and March respectively.

Inside the lake, the highest value recorded is 2720 oocysts/L in the month of April at the 2 meters depth, while the lowest value obtained is 88 oocysts /liter in the month of September at the surface of the lake (Fig. 2 and 3).

The values of the Giardia cysts dynamics follow the same trend like those of the oocysts of Cryptosporidium (Fig. 3 and 4).There is a relatively higher density of cysts at the inlet of the lake, with respect to the outlet. The values obtained reveal that the maximum number of cysts at the inlet was 352 cysts/L in the month of April, while the lowest was 33 cysts/liter in the month of September.

In the Mingoa 2 point, the highest cysts recorded were 452 cysts/liter in the month of May, while the lowest was 10 cysts/liter in the month of October. There was a relative increase in cysts density from the surface to the bottom of the municipal lake. The highest values of cysts determined was 1713 cysts/ L at the 2 m level in the month of May, while the lowest value obtained was 24 cysts/L at the surface, during the month of September.

The values of turbidity and suspended solids increase from the surface to the bottom of the lake. The highest values of turbidity are 637.5 FTU at the lowest point of the lake analysed, this is during the period of July while the lowest value was 50 FTU at the surface of the lake, during the period from March to April. There were more suspended solids at the inlet of the lake with respect to the outlet. The suspended matter varied from a maximum value of 1500 mg/L at the entrance of the lake to 50 mg/L at the outlet of the lake in the months of September (Tables 1 and 2).

Ammonia values in the study points ranged from 0.25 mg/L to 4.0 mg/L. There was an increase in the tenor of the ammonium ions from the surface to the bottom layers of the municipal lake. The inlet was generally charged with a higher content in the ammonium ion with respect to the outlet points assessed (Table 3).

DISCUSSION AND CONCLUSION

The (oo)cysts are transported into this eutrophic ecosystem by the Mingoa stream which crosses many inhabited quarters of the Yaounde neighbourhood. It also receives untreated waste from the Messa residential quarter non-functional water treatment plant. The prevalence of Cryptosporidium spp. oocysts and Giardia spp. cysts during the rainy season is an indication that contaminated water may be important in its distribution as reported by Robertson, et al. (2006). The overall water sanitation and hygiene related death (99.8 percent) occurs in developing countries and 90 percent are deaths of children (WHO, 2003).

Giardiasis and cryptosporidiosis are waterborne diseases that are spread through water in which water acts as a passive carrier for the transmissive forms of the infecting pathogens. These diseases depend also on the sanitary and environmental conditions of the region in question (Ajeagah, et al. 2005; Cifluentes et al. 2006). The protozoan pathogen C. parvum has been considered as a leading cause of waterborne gastroenteritis (Santos, et al. 2004). Due to its small size (5 µm), low specific gravity (1.05 g/ c3) and negative surface charge, C. parvum oocysts are generally considered to move through watersheds from their areas of emission to drinking water reservoirs with little attenuation of their population density in the stream channel (Marly et al. 2001), however the transport of oocysts in a lentic medium may be mediated by interactions with suspended sediments and by subsurface filtration and removal in streambed sediments (Dia & Boll 2006). The application of settling columns and flame experiments have demonstrated that C. parvum oocysts attachment to several inorganic and organic sediments under varying water quality conditions may drastically influence the effective in-stream settling velocity of oocysts in natural mediums (Hijnen et al. 2005). These hydrostatic interactions with debris that are present in water could vary the settling velocity of the protozoan in the lake ecosystem. The rate of the downward transport on the oocysts concentration and reduction within the water column is between one and three orders of magnitude less than that caused by advection and dilution, depending on the strength of the hydrodynamic forcing in the water column (Brookes et al. 2006).

Table 3: Values of ammonium nitrogen (mg/L) in the Mingoa stream and the municipal lake

Month/Points Mingoa 1 (inlet) Lake 1 (0 m) Lake 2 (1 m) Lake 3 (2 m) Mingoa 2 (Outlet)
February 1.5 0.4 0.15 0.55 0.35
March 1.0 0.25 1.0 1.35 1.0
April 2.9 0.25 0.5 0.90 0.25
May 1.6 1.0 2.2 3.40 2.25
June 1.5 0.63 0.75 1.00 0.61
July 1.38 1.13 1.35 2.13 1.01
August 2.66 1.59 1.96 3.90 1.51
September 4.0 1.36 2.41 2.96 1.27
October 3.6 1.25 2.65 3.50 1.35
November 3.5 1.50 3.05 3.90 1.40

 

The (oo)cysts are transported and deposited in the water column by mechanisms of attachment, detachment and straining (Bradford, 2005). Their transfer from the surface to the water sediments influences their movement in the lake ecosystem. Hydrodynamic interactions between an overlying flow and a sediment bed cause the (oo)cysts to accumulate in the sediments and reduce their concentration in the uppermost layers of the municipal lakes. Their association with other suspended particles increases both their effective settling velocity and the rate at which they are transferred to the sedimentary layer (Karim et al. 2004). This pathogen –sediment interaction plays an important role in regulating the concentration of these (oo)cysts in the hydrosystem (Searcy et al. 2006).

The organic particles in water play an important role in the transportation of these emerging pathogens according to Medema et al. (1998), these (oo)cysts are generally linked to suspended particles in the water column. This adsorption influences the speed of sedimentation of the protozoa in the aquatic medium; this also increases the difficulties of purification of these parasites by water treatment plants (Weiss et al., 2005).

The rapid urbanization of the city of Yaounde, places on the population an inadequate water supply and insufficient sanitary resources, this is associated with increased human activity and this renders the lake highly polluted and a resultant accumulation of pathogens (Ajeagah et al., 2006). This is manifested by an increase in the values recorded for the suspended solids, the turbidity and the tenor in ammonia from the surface water of the lake to the bottom layers. This same trend that has been observed for the oocysts and the cysts suggest the possibility of an adsorption model between the (oo)cysts and the particles that are present in the water column, which necessitate the transportation of the biomolecule inside the aquatic system. There is therefore the presence of receptor sites on the oocysts and cysts which are responsible for the binding with the organic and inorganic matter present in water and their consequent displacement with the solvent like an entity.

The lake subsequently acts as a reservoir of pathogenic organisms which are likely to accumulate at the bottom sediments (Kistemann et al., 2002). These micro-organisms are a risk to public health, taking into consideration the fact that the Mingoa stream is one of the tributaries that is exploited for potable water production in the city of Yaounde, the water is also being used for recreational activities and fishing which places the population at a high health risk. This can be at the origin of epidemic episodes (Giovanni et al., 2006). The dysfunction of the waste water treatment systems places the population at increasing clinical risks as the protozoa

G. lamblia, the zoonotic C. parvum and the anthroponotic C. hominis are the major causes of enteric diseases throughout the world (Guy et al. ,2006, Diaz et al. 2003, Hunter & Thompson 2005). The absence of a garbage treatment mechanism has been known to expose many children and the immunodepressed to severe gastroenteritis in the community (Diaz et al., 2003).

These parasites are hyper endemic in areas that are lacking waste water and a drinking water treatment plant (Redlinger et al., 2002). The intensity of environmental stressors is geographically specific and may have different effects on the survival and persistence of pathogens in the environment (Alarcon et al., 2005). The reclaimed waste water does pose a significant health risk to humans due to the high pathogens levels and the lack of an effective disinfectant methodology (Geurden et al., 2005). There is a similar variation trend between water turbidity and the oocysts biodynamic in the various layers of the lakes (Sarco et al., 2006), as well as the relationship with the suspended solids which are necessary for the removal of the oocysts (Hu et al., 2004). The Yaounde municipal lake acts like a purification station because it reduces the density of parasites between the inlet and the outlet of the Mingoa stream. This leads to an accumulation of these enteropathogens in the lower layers of the municipal lake which can easily be released into the whole of the Mfoundi river basin of Yaounde, which can be at the origin of water related epidemics, in the cases where there is a perturbation of the water system, either by heavy rainfall or by other human activities. The high values of suspended solids and the consequent increase in the levels of turbidity in the municipal lake as presented in tables 1 and 2 reveals the possibility of anthropogenic effects on this eutrophic ecosystem. These actions can be at the origin of water related outbreaks of diarrhoea, for the entire community which relies on this water system for potable water production (Standish-Lee & Loboschefsky, 2006).

High concentrations of the ammonium ions in the medium can probably increase the inactivation of the oocysts by their ability to penetrate into the walls of the oocysts and the membranes of the sporozoites. The maximum tenor in the ammonium ion in the municipal lake is 3.90 mg/L. The penetration of this ion into the double layers of the oocysts is facilitated by the pH values in the medium which are not adapted to the viability of the emerging parasites (Jenkins et al., 1998). The presence of some chemical elements such as sodium, chlorine and potassium ions reduces the process of excystation of the (oo)cysts (Kato et al., 2001). The Apicomplexan and the Sarcomastigophora isolated and identified in the water system are capable of contaminating the public drinking water supply, as well as the water used for recreational purposes (Collick et al., 2006).

Cryptosporidium spp. oocysts and Giardia spp. cysts have been isolated and identified in the municipal lake of Yaounde. The results reveal an increase in (oo)cysts density from the surface layers to the bottom depth of the lake. There is a considerable decrease in the biodynamic of the resistant forms of these pathogens between the inlet and the outlet of the lake. This suggests the characteristic purification properties of this lentic ecosystems and the application of this mechanism in sedimentary basins of water treatment plants. The lake acts as a reservoir for Cryptosporidium oocysts and Giardia cysts in the ecosystem. The same trend recorded between the turbidity, the suspended solids with the (oo)cysts population dynamics suggests the possibility of an adsorption model in the transportation of the transmissive forms of the parasites in the lake ecosystem analysed. The accumulation of pathogenic micro-organisms at the bottom layer of the municipal lake exposes the population to an outbreak of giardiasis and/or cryptosporidiosis in cases that the resistant forms of the parasites are released into the entire river basin by floods in the event of heavy rains or anthropogenic activities.

ACKNOWLEDGEMENT

This study has been carried out with the material assistance of AIRE Development. Grants from this project have been used in the purchase of reagents and equipment for the detection of the pathogens and the physico-chemical analysis of the samples.

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