The Topic of This Month Vol.22 No.7(No.257)
Cryptosporidium parvum is an enteric protozoon, one of coccidian parasites. It's infection results from oral ingestion of oocysts (with a diameter of 4.5-5.4X4.2-5.0ƒÊm) excreted in patients' stools. The number of oocysts excreted by one patient may reach as high as 1010. In principle, the clinical symptoms are nonhemorrhagic watery diarrhea, abdominal cramps, and appetite loss (see p. 161 of this issue). There is no known effective drug for treatment of cryptosporidiosis, nevertheless most normal people will recover spontaneously. Immunosupressed patients, however, tend to become inveterate, and severe cases to turn fatal (see p. 162 of this issue). Infection of the gallbladder, bile duct, and respiratory organs is known in immunosupressed patients. Although C. parvum alone used to be regarded as causing infection among immunologically healthy individuals, C. meleagridis (avian origin) has recently been found in human infection by nucleotide sequence analysis (see p. 163 of this issue). It seems possible that some new pathogenic species could be found in the future. Apart from this, infections of AIDS patients with C. baileyi or C. muris have been reported.
Giardia lamblia (syn. G. duodenalis or G. intestinalis ) is also a protozoon of one of flagellates. It's trophozoite has such morphological characteristic as; four pairs of flagella and a ventral disc. Only asexual reproduction is so far known. The cysts, 5-8X8-12ƒÊm in size, are excreted in patients' stool. Infection is acquired upon oral ingestion of the cysts. Infection occurs in the duodenum and upper small intestines, sometimes spreads to bile duct and gallbladder. The main symptoms are nonhemorrhagic diarrhea, abdominal cramps, and steatorrhea (see 161 and 162 of this issue). Metronidazole is the treatment most often applied.
Cryptosporidiosis and giardiasis have been classified into the category IV notifiable infectious diseases in the National Epidemiological Surveillance of Infectious Diseases (NESID) under the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the Infectious Diseases Control Law) enacted in April 1999. Physicians who suspected the illness from clinical symptoms must notify the governor of the patients through the nearby health center within seven days after the illness has been confirmed by etiological diagnosis.
Cryptosporidiosis patients notified before the 2nd week of June 2001 after enactment of the Infectious Diseases Control Law have counted as few as 13 (Table 1). Eight of them were imported cases and the main region of acquiring infection has been Indian Subcontinent. However, as many as 209 giardiasis cases have been notified during the same period. The incidence by month and by region of acquiring infection is shown in Fig. 1. The estimated areas of acquiring infection were; overseas for 93 cases, such as India for 38 cases and Thailand for 17 cases, within this country for 84 cases, and unknown for 32 cases. No seasonality was seen in the occurrence of domestic cases. The age distribution by sex of patients in Japan (Fig. 2) shows that most patients notified were adults, with a peak at 20-34 years of age followed by a lower peak at 50s. Patients aged less than 20 numbered only seven. There were more male than female patients at a ratio of 3:1. Reports from other countries tell that giardiasis is prevalent among children; a recent surveillance performed in USA shows a highest peak in children at ages of 0-5 years followed by somewhat a lower peak in adults at ages of 31-40 years. This indicates that the adult group has the possible exposure to infected children (CDC, MMWR, Vol. 49, SS07, 2000). Following the above results, it was pointed out that the objects of parasite examination in Japan involved a larger number of particular risk groups such as travelers to developing countries. For the bona fide trend of incidence, pathogen surveillance must be expanded to cover all diarrheal cases.
In regard to the methods for patients' fecal tests for protozoa, those for cryptosporidiosis involved such methods that enhance the detection efficiency, including fluorescent antibody staining (Table 1). On the other hand, for about 75% of tests for giardiasis, conventional light microscopy of stool specimens is still in use; use of cyst concentration or staining has been limited to the approximate of 25%. For both protozoa, fluorescent antibody reagent kits have already been developed, which have contributed to heighten the detection efficiency (health insurance does not apply to such kits, though). Regarding the protozoan detection methods, Protozoological Analytical Manual-Cryptosporidium and other enteric protozoa-has been distributed by the National Institute of Infectious Diseases presenting test procedures in accordance with the laboratory's capability.
Those protozoan parasites are transmitted via drinking water or food, or in some cases by contact infection. They have been placed under the category IV notifiable diseases for the occurrence of patients must be detected as promptly as possible for the prevention of large-scale outbreaks of infection mediated by drinking water. Waterborne cryptosporidiosis outbreaks have often been reported in USA and UK after mid 1980s. In the 1993 incident occurring in Milwaukee, Wisconsin, more than 400,000 citizens were infected. A similar trend has been seen in giardiasis; as many as 42 waterborne outbreaks were reported in USA during 1965 and 1980. In Japan, outbreaks of waterborne cryptosporidiosis occurred in a building complex accommodating a number of business clients in Hiratsuka City, Kanagawa Prefecture in 1994 (see IASR, Vol 15, No. 11) and in Ogose Town, Saitama Prefecture from drinking water in 1996 (see IASR, Vol. 17, No. 9). In the latter outbreak, about 70% (8,812 people) of the town population were infected.
The Ministry of Health and Welfare (MHW; at that time), taking this situation seriously, organized a study group for urgent control of Cryptosporidium and other enteric protozoa in drinking water in August 1996 (reorganized in August 1997). The study group compiled a tentative guideline for Cryptosporidium control in drinking water (Notice No. 248 by Water Supply Division, Health Service Bureau, MHW October 1997) to present preventive and emergency measures to water utilities and prefectures (partly amended in June 1998). Further, cryptosporidiosis and giardiasis were placed under the category IV notifiable diseases when the Infectious Diseases Control Law was enacted in order to intensify the patient surveillance.
In addition to the waterborne outbreaks, an outbreak involving nine patients who took part in experimental animal infection is known (the Proceedings of the 7th Annual Meeting of Association of Animal Protozoiases, April 1993); there have been only few reports on sporadic cases (see p. 162 of this issue).
Contamination of water with Cryptosporidium or other pathogenic protozoa brings forth a serious problem because of the difficulty of their disinfection or removal once contamination occurs. The clearance efficiency of conventional water treatment can be expected to be 99.9% for Cryptosporidium and 99.99% for Giardia . (Oo-)cysts of protozoa, particularly of Cryptosporidium , are highly resistant to chlorine, therefore chlorine disinfection is not feasible. If source water or drinking water including well water contains protozoan parasites, report to the Ministry of Health, Labour and Welfare is requested according to the manual for health risk management of drinking water (Notice No. 162 by Water Supply Division, Health Service Bureau, MHW on April 10, 1997). In line with the request, contaminations of 29 rivers in 13 prefectures were reported during April 1999 and June 2000 (see p. 164 of this issue).
In addition, contamination of swimming pools with Cryptosporidium (accidents from fecal contamination) has captured the attention of Europe and USA (see p. 171 of this issue). Because of the inefficacy of chlorine disinfection, Cryptosporidium contamination of swimming pools might lead to outbreaks of infection. Such general hygienic management as maintenance of environmental sanitary conditions and limitation of use of recreational water facilities by diarrheal cases must be intensified all over Japan.