Predisposing Conditions And Pathophysiology

IB results from the ingestion of C. botulinum spores. Even though honey is a known source, in about 85% of patients the source is unknown. BI cases occur from six days to 12 months of age and not later. Information derived from a mouse model and clinical cases suggest that transient absence of competitive microbial intestinal flora and/or alteration in motility or pH enables outgrowth of vegetative forms from ingested spores. Recently, weaned infants that have been exclusively breast-fed and, when changes of intestinal flora occurs, are at risk for IB.

Replicating C. botulinum, and occasionally C. baratii and C. butyricum, produce distinctive botulinal neurotoxins (types A-G) of high potency. After systemic absorption, toxin binds to receptors on presynaptic nerve endings of cranial and peripheral nerves and blocks acetylcholine release (15).

Excretion of the organism has persisted for as long as 158 days after the onset of constipation, well after clinical recovery had occurred. The syndrome has occurred in both breast-fed and bottle-fed infants, and the role of type of feeding is yet unsettled (16).

Colonization is believed to occur because normal bowel flora that could compete with C. botulinum have not been fully established.

Risk factors for IB are multifactorial and include breastfeeding, and the introduction of first-formula feeding, consumption of honey, and residence in a region of high spore density and soil disruption (13). Constipation appears to be a risk factor but also is an early manifestation of intoxication (17).

Breastfeeding is a risk factor for IB in all studies (13,16-21). This may be the case because it truly predispose to illness (13,17,20), or that it slows the illness to permit hospitalization (16). However, among hospitalized infants the formula-fed reported from California (16), had a mean age of onset (7.6 + 8.4 weeks) that was significantly less than that of their breast-fed counterparts (13.7 + 8.4 weeks). The younger age at onset for formula-fed infants may reflect their earlier availability of suitable ecologic niches for C. botulinum in the intestinal flora of the formula-fed infants (13,18), as well as the lack of immune factors that are contained in human milk. Long et al. (13), who reported 44 patients with IB from Southeastern Pennsylvania, found that the majority of their patients had just formula feedings or other food introduced within four weeks of onset. The resident gut microflora is capable of blocking the outgrowth and multiplication of C. botulinum spores. The difference in the fecal flora of breast- and formula-fed infants may account for the increased earlier susceptibility of formula-fed infants to IB. Infants fed human milk have more acidic feces (pH 5.1-5.4) that contain a large number of Bifidobacterium (~ 1010/g). Clostridium (as spores) are virtually absent (22).

In contrast, formula-fed infants have less acidic feces (pH 5.4-8.0), that also contain Clostridium spp. as well as other anaerobes and facultative bacteria (18). The difference in pH may be important, because multiplication of C. botulinum and toxin production declines with reduced pH.

Preformed toxin has not been identified in food ingested by the infants, but the organism has been identified in honey, vacuum cleaner, dust, and soil. C. botulinum organisms, but no preformed toxin, were identified in six different honey specimens fed to three California patients with IB, as well as from 10% (9/90) of honey specimens studied (23). By food exposure history, honey was significantly associated with type B IB. In California, 20% (56 of 272) of hospitalized patients had been fed honey prior to onset of constipation (24), in Utah 83% (10 of 12) (19), and in Southeastern Pennsylvania 14% (6 of 44) (13). Worldwide, honey exposure occurred in 35% (28/75) of hospitalized cases. Of all food items tested, only honey contained C. botulinum organisms.

The organism and its toxin have rarely been identified in the feces of normal infants (25). C. botulinum was isolated from the stools of three normal control infants and nine control infants who had neurologic diseases that clearly were not IB (19). These infants were termed as "asymptomatic carriers" of the organism. The occurrence of the asymptomatic carrier state suggests that a diagnosis of IB cannot be made on a basis of culture results alone, but must rest on historical and physical confirmation of progressive bulbar and extremity weakness with ultimate complete resolution of symptoms and findings over a period of several months.

A distinct seasonal incidence to IB was observed in one study done in Utah (19). All the cases were reported between March and October with no reported cases during the winter months. The seasonal incidence suggests that the temperature and moisture factors that favor proliferation of C. botulinum in the soil could be of major importance. No apparent temporal relationship existed between cases and season, temperature, or rainfall in the 44 cases reported from Southeastern Pennsylvania (13).

A common set of environmental features was found to be characteristic of the home environment of children with IB and asymptomatic carriers, and includes nearby constructional or agricultural soil disruption, dusty, and windy conditions, a high water table, and alkaline soil conditions (19). The conditions of high soil water and alkaline content, which are favorable for the growth of C. botulinum (11), were found near the homes of all affected infants.

The dissemination of the organism appeared to be further enhanced by construction and agricultural soil disruption as well as windy conditions near the homes of most affected infants and asymptomatic carriers.

About half of patients' fathers in the cases reported in Pennsylvania (13) had occupations that brought them into daily contact with soil. Spores were recovered from yard soil, window sills, cribs, or fathers' shoes in seven of nine instances in which environmental sampling was done. Forty three of the 44 cases occurred in infants who resided around the city of Philadelphia, and only 1 infant was from the city. A possible explanation for this discrepancy is the differences in the disruption of soil between the city and surrounding areas and little occupational contact with soil in the city compared to the surrounding areas.

The ubiquitous distribution of C. botulinum spores in nature allows for their ingestion by many infants (5). The fact that ingested spores can germinate in some, but not all, infants generally between one and six months old indicates that host factors unique to this age play a central role in pathogenesis. Host factors are of great importance, a point emphasized by the broad spectrum in the severity of disease.

5 Common Skin Problems Answered

5 Common Skin Problems Answered

Our skin may just feel like a mere shield that protects us from the world outside. But, the fact is, its more than just the mask that keeps your insides in. It is a very unique and remarkable complex organ that reflects our general health.

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