Removal of parasitic protozoa from water using a mobile water filtration apparatus intended for field use by military or emergency personnel

Military Medicine, Jan 2003 by Robertson, Lucy J

Approximately 3,200 L of water were inoculated with Cryptosporidium oocysts and Giardia cysts. The contaminated water was filtered through a Berkefeld Filter, type TWA 3, as used by the Norwegian army. Nine 10-L samples of filtered water and four 10-L control samples of unfiltered water were analyzed for Cryptosporidium oocysts and Giardia cysts. On average, 1,920 Giardia cysts and 2,735 Cryptosporidium oocysts per 10 L were detected in the unfiltered water. Between 0 and 2 Giardia cysts and between 2 and 47 Cryptosporidium oocysts were detected in the filtered 10-L samples. Percentage removal of parasites was between 99.8 and >99.95% for Giardia (2.98 to >3.28 log removal) and between 98.3 and 99.9% (1.76-3.14 log removal) for Cryptosporidium. The Berkefeld filter TWA 3 complies with published recommendations for municipal water supply for removal of Giardia but does not always comply with such regulations for Cryptosporidium.

Introduction

Water courses can be contaminated by pathogenic microorganisms. including viruses. bacteria. and parasites. Generally, such pollution occurs due to discharge of sewage effluent or contamination by agricultural waste, for example from slurry spraying or pasturing of livestock. In provision of municipal water supply, the risks of waterborne infection from contaminated sources are reduced by judicious selection of water sources for supply and the provision of water treatment processes, which are aimed at removing and/or inactivating the pathogens.

Within the past 25 years, there has been considerable interest in two intestinal protozoan parasites, Cryptosporidium parvum and Giardia intestinalis, which are known to have a widespread distribution in raw water supplies globally and have been responsible for many community-wide waterborne outbreaks of infection, particularly in the United States and the United Kingdom. Various features of these two parasites facilitate their waterborne transmission1 including the following:

- Relatively low host specificity (both parasites are zoonotic, infecting a range of animal species as well as man),

- High numbers of the transmission stages of both parasites (oocyst for Cryptosporidium, cyst for Giardia) are excreted by infected hosts,

- The robust nature of cysts and oocysts enables extended periods of survival even in some unfavorable environments, including resistance to some disinfectants used in the water industry,

- The small size of oocysts (4.5-6 (mu)m) and cysts (8-12 (mu)m length x 7-10 (mu)m width) allows penetration of standard water-treatment filters,

- The low infectious dose of each parasite means only a small number of infectious oocysts or cysts need to be ingested to establish infection in a susceptible host.

For both parasites, infection is generally characterized by diarrhea, which may last for a few days or persist for several weeks or longer. Additionally, malaise, fever, abdominal pain, anorexia, and nausea may be associated with infection. Asymptomatic infection can also occur with both parasites. Diagnosis is generally by detection of the parasites (Cryptosporidium oocysts, Giardia cysts, or occasionally, Giardia trophozoites) in the patients' stools. Diagnosis of Giardia infection is considered to be problematic because of intermittent cyst excretion. Although there are effective chemotherapeutic treatments for giardiosis, there is currently no chemotherapeutic treatment for cryptosporidiosis, and in immunocompromised individuals (e.g., AIDS patients) the disease can be life threatening.

Whereas both of these parasites have caused outbreaks of disease via municipal water supplies, the provision of a safe water supply for troops and other military, emergency, or similar personnel in a field situation is likely to be even more difficult. Field conditions vary greatly from one geographic locale to the next, and requirements and methods for providing safe water often change according to environment.2 Field conditions in modern warfare can change; urban warfare may require deployment of troops into an area that previously had modern public utilities such as potable water lines, sanitary sewers, and waste disposal.2 Overnight, an area such as this can change into a disaster zone where all water, food, and services should be suspected of contamination or do not exist.2 Furthermore, in a hostile environment, water supplies may be deliberately contaminated.

Natural disasters, such as earthquakes, in which military and emergency personnel may be deployed, can also destroy and/or damage public utilities, so that they cannot be relied upon to operate effectively, if at all.

The possible impact on military and emergency personnel if these infections are acquired in the field is important. Diarrheal disease is recognized as a potential cause of substantial morbidity among troops and is the dominant military medical concem among deployed units.3 Retrospective studies have shown that diarrheal illness is one of the most common medical problems for deployed troops of many nationalities4-7 and has had a significant impact on U.S. military forces during short-term deployments to less developed areas.4,5

Furthermore, not only are the symptoms of cryptosporidiosis and giardiosis debilitating, affecting working capacity, but the risk of secondary spread of infection should also be considered. The excreted parasites are immediately infectious, not requiring a period of maturation in the environment, and may spread rapidly through closely quartered personnel, particularly in an environment where hygiene is not ideal. In a recent outbreak of cryptosporidiosis in a group of German armed forces involved in a 5-day field exercise, approximately 200 of 450 participating soldiers (over 40%) experienced acute gastroenteritis because of this infection.8