Dr. Lucy Robertson, a speaker at the 8th Central American and Caribbean Congress on Parasitology and Tropical Medicine 2007, points out that as countries strive to improve their standards of public health, we should find it intolerable to accept the transmission of these infections via drinking water anywhere.
Of the parasitic infections with a global impact, both cryptosporidiosis and giardiasis come relatively low on the list. However, acute infections with both can be extremely debilitating in the short-term, the paucity of chemotherapy for cryptosporidiosis can mean that it may be a fatal infection for the immunocompromised, and refractory giardiasis can be associated with prolonged morbidity, even after apparent recovery from the infection. Both infections most surely contribute to the global death toll from diarrhoeal infections, particularly in children. Currently this stands at 2.2 million children annually; one every 14 seconds.
The high excretion rate, low infective dose, and robust transmission stages of both parasites lend themselves to dissemination by drinking water, and there have been many extensive waterborne outbreaks of both parasites in which hundreds or thousands of individuals have been infected. On the whole, outbreak reports are usually from industrialised countries (Karanis et al, 2007). For example, in 1993 over 400,000 people developed cryptosporidiosis in Milwaukee, USA due to contamination of the drinking water supply (MacKenzie et al, 1994) and, more recently, in 2004, in Bergen, Norway, over 1500 people suffered from giardiasis due to water supply contamination (Robertson et al, 2006).
At the 8th Central American and Caribbean Congress on Parasitology and Tropical Medicine* in Havana, Cuba (4th - 7th December 2007), various groups gave presentations concerning different aspects of cryptosporidiosis and giardiasis, but only one plenary session was devoted to the detection of these parasites in water and other environmental matrices. YET many of the delegates come from countries or regions in which drinking water supplies are more vulnerable to contamination, or where water treatment is minimal: these populations are obviously at greater risk from these diseases, and, in addition, the exposed populations are often more likely to be susceptible to more severe symptoms from both infections. Though drinking water transmission must occur, for these communities cryptosporidiosis and giardiasis are rarely seen as a pressing problem and outbreaks go unreported.
There are various possible reasons for this situation, including:
where drinking water infrastructure is poor, both infections could be so widespread that outbreaks cannot be identified against background infections
persistent exposure has resulted in some degree of immunity amongst the adult populations in such communities.
Nevertheless, as countries strive to improve their standards of public health, we should find it intolerable to accept the transmission of these infections via drinking water anywhere.
Over 490 delegates attended the Congress, 290 from Cuba, and 202 from other countries, particularly Latin America, but also including Japan, Europe, Africa, and Central Asia, in an impressive programme organised by the Pedro Kourà Institute of Tropical Medicine in Havana. In my presentation I was attempting to describe the reasons for assessing water and food as vehicles for these infections, and the various methods and approaches by which this could be accomplished. By illustrating the web of interactions between water, food, parasites, and human health, I hoped to demonstrate that by having knowledge of contamination, suitable strategies could be implemented to reduce or eliminate these routes of transmission. The enthusiasm and dedication of the many delegates at the Congress was notable, but from the questions after my talk it was clear that to many of them the technical and political aspects of analysing water supplies for parasites seemed insurmountable. This is understandable; as the parasites cannot be cultured like bacteria, detection of both parasites in drinking water involves separating the individual transmission stages from the water. It is a costly procedure with multiple steps, including immunomagnetic separation and detection by immunofluorescent microscopy. Nevertheless, identification and interruption of transmission routes for these parasites is essential in their control, and with the 2015 Millenium Development Goals deadline approaching (MDG 4, 6 & 7 indicators are relevant here, see MDG progress chart), the time is ripe for global players to step in and ensure that drinking water supplies everywhere are parasite-free.
*The Central American and Caribbean Congress on Parasitology and Tropical Medicine is a biennial event: Cuba 2007 included 32 plenary sessions, and over 350 poster presentations, as well as 4 pre-congress workshops, 11 symposia, and 9 round table discussions. The next Congress is scheduled for 2009 in Costa Rica.
References:
1. Karanis, P., Kourenti, C. & Smith, H. 2007. Waterborne transmission of protozoan parasites: a worldwide reveiw of outbreaks and lessons learnt. J. Water Health 5(1), 1-38.
2. Mac Kenzie W.R., Hoxie N.J., Proctor M.E., Gradus M.S., Blair K.A., Peterson D.E., Kazmierczak J.J., Addiss D.G., Fox K.R., Rose J.B., & Davis, J.P. 1994. A massive outbreak in Milwaukee of Cryptosporidium infection transmitted through the public water supply. N. Eng. J. Med. 331(3), 161-7.
3. Robertson L.J., Hermansen, L., Gjerde, B.K., Strand, E., Alvsvåg, J.O. & Langeland, N. 2006. Application of genotyping duirng an extensive outbreak of waterborne giardiasis in Bergen, Norway during autumn and winter 2004. Appl Environ Microbiol 72, 2212-2217.
4. UN MDG progress chart, indicators for MDG 4, 6 and 7: namely reducing under 5 child mortality by 2/3, the combat of malaria, HIV/AIDS and other diseases, halving the proportion without improved drinking water.
Editors note:
1. To view relevant Global Health content which is freely available on Google, use this link:
http://www.google.com/coop/cse?cx=011480691189790707546%3Azwixxwtzvyu&hl=en
Then enter this search: (giardiasis or cryptosporidiosis) AND outbreaks
2. CABI will publish in August 2008 a new book, Giardia and Cryptosporidiosis, edited by M. G. Ortega-Pierres et al. Read more at: http://www.cabi.org/bk_BookDisplay.asp?PID=2109
Dr. Lucy Robertson is based at:
Seksjon for Parasittologi
Institutt for mattrygghet og infeksjonsbiologi
Norges veterinærhøgskole
PO boks 8146 Dep
0033 Oslo
NORWAY.
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