We believed studying animals susceptible to colonization with H. pylori would greatly facilitate the studies aimed at clarifying its pathogenicity. Such a test model is advantageous in that the animals are easy to handle, widely available, and inexpensive, thus permitting a wide variety of experiments to be carried out. As a result, we achieved continuous colonization with H. pylori in the gastric mucosa of nude mice and euthymic mice in 1990 [2], using freshly isolated strains of H. pylori obtained from patients with gastritis, gastric ulcer, and duodenal ulcer. Moreover, we developed the H. pylori infected rodent model using a Mongolian gerbil which was observed severer inflammation and the ulceration in 1996 [3]. In addition, the gastric mucosa would not be colonized unless freshly isolated strains of H. pylori was used, by the established strains.

To establish the H. pylori infected mouse model, the challenged H. pylori inocula such as two-milliliter aliquots of the culture fluid of H. pylori with a concentration of 10⁸ organisms/ml (adjusted as the report) were prepared on a one-time basis.

This H. pylori infected model to which extraordinary high concentrated inocula is administered is one of the H. pylori infected case by the oral transmission of H. pylori which is unrealistic large amount of H. pylori. Then, what is the source of natural H. pylori transmission in case of oral transmission? One example is H. pylori infected human. However, this source is not highly concentrated H. pylori. Therefore, it is speculated that the intimate interaction is required for H. pylori transmission.

There have been several reports about the mode of transmission of H. pylori. It is suggested that the representative route of H. pylori transmission is presumably close personal contact, as mentioned above, special among the familial members. Instead of demonstrating the H. pylori transmission among the humans, we demonstrated the H. pylori transmission from challenged to non-challenged mice in a single cage using the mouse model we developed previously [2].

The results [4] are following:

Six mice were challenged with H. pylori inocula; one group consisted of one challenged mouse 1 week after inoculation raised with four non-challenged mice in a single cage. For the single cage, a polycarbonate cage or a mesh floor cage was used. The three groups were kept in a polycarbonate cage and the other three groups kept in a mesh floor cage to avoid H .pylori transmission through stool. During 3 weeks after co-raising of H. pylori challenged and non-challenged mice, H. pylori was detected in the stomachs in 3 of 12 non-challenged mice in the polycarbonate cage and in 2 of 12 non-challenged mice in the cage with a steel mesh floor. H. pylori was detected from saliva or stool in two non-challenged, infected mice in the polycarbonate. Moreover, RAPD fingerprinting of the total five strains isolated from five non-challenged infected mice both cages showed the same pattern and concordance with that of the challenged strain and the strains isolated from challenged mice. After coraising for 1 or 2 weeks, H. pylori was detected in the stomach in only 1 of 48 non-challenged mice in both cages. Moreover, food and drinking water is thought to be the source of H. pylori infection through the oral route, such as the H. pylori infected person. Waterborne H. pylori transmission was previously reported [5].

The Hp (H. pylori) status of their 82 parents (41 fathers and 41 mothers) was positive in 57 (32 males and 25 females) and negative in 25 (9 males and 16 females). The Hp status of the parents had the same trend according to the age. The relationship between several factors and Hp infection of children (17 positive and 63 negative) was evaluated as shown in Table 1. The factors were age (1-10, 11-20, 21-38 years old), sex, water supply (well water and municipal water), Hp status of father and mother, cigarette, alcohol, antibiotics use, and NSAIDs use. The Wilcoxon test was used for age and Fisher’s exact test for the other factors. Age, sex, and history of drinking well water are substantially associated with Hp infection. The history of municipal water drinking is significantly negatively associated with Hp infection. Therefore, logistic regression was used to evaluate the relationship between age, sex, or history of drinking well water and Hp infection of children. Then, the history of drinking well water is substantially associated with Hp infection after adjustment for age and sex (odds for 1 year: 1.19 and 95% CI: 1.08-1.32) and, age and sex is not significantly associated with Hp infection. Next, we evaluated the duration of drinking well water and found a strong significant association with Hp prevalence in 80 children as shown in Table 2. Upper gastrointestinal endoscopies were performed on selected family members with symptoms, and H. pylori strains from these families were isolated and RAPD performed to explore the route of H. pylori infection. H. pylori prevalence in the 41 families increased with age, and there is strong relationship between H. pylori serological prevalence and a history of drinking of well water. Among the people who have a history of drinking well water, H. pylori prevalence in those at least 10 years old was 85.3%, which is significantly higher than that in those less than 10 years old (25%) and no history of drinking well water (6.3%). There were 5 families with H. pylori serologically positive members who have drunk well water. RAPD fingerprinting of isolated H. pylori strains from these family members also suggested that the origin of H. pylori infection was well water [6].

In spite of Japan being a developed country, the reported prevalence of H. pylori infection is higher than that of other developed countries. This indicates that many houses have private wells and had drunk well water rather than the municipal water with good sanitation 35 years ago in Japan. Municipal water with good sanitation was available to 69.4% of Japan at that time. The availability of municipal water was increased about 5% every 5 years and reached 94.7% in 1990 and increasing in subsequent years. It is speculated that most H. pylori transmission in Japan depends on waterborne transmission and the occurrence of its transmission is strongly associated with the duration of the history of drinking well water.

CONCLUSION

1.       Warren JR, Marshall B (1983) Unidentified curved bacilli on gastric epithelium in active chronic gastritis. Lancet 1: 1273-1275.

2.       Karita M, Kouchiyama T, Okita K, Nakazawa T (1991) New small animal model for human gastric Helicobacter pylori infection: Success in both nude and euthymic mice. Am J Gastroenterol 86: 1596-1603.

3.       Matsumoto S, Washizuka Y, Matsumoto Y, Tawara S, Ikeda F, et al. (1997) Induction of ulceration and severe gastritis in Mongolian gerbil by Helicobacter pylori infection. J Med Microbiol 46: 391-397.

4.       Karita M, Matsumoto S, Kamei T, Shinohara K, Sugiyama T (2005) Direct transmission of H. pylori from challenged to non-challenged mice in a single cage. Digest Dis Sci 50: 1092-1096.

5.       Hulten K, Enroth H, Engstrand L (1998) Presence of Helicobacter species DNA in Swedish water. J Appl Microbiol 85: 282-286.

6.       Karita M, Teramukai S, Matsumoto S (2003) Risk of Helicobacter pylori transmission from drinking well water is higher than that infected intrafamilial members in Japan. 48: 1062-1067.