Exposure to viral and bacterial pathogens among Soay sheep (Ovis aries) of the St Kilda archipelago.

We assessed evidence of exposure to viruses and bacteria in an unmanaged and long-isolated population of Soay sheep (Ovis aries) inhabiting Hirta, in the St Kilda archipelago, 65 km west of Benbecula in the Outer Hebrides of Scotland. The sheep harbour many metazoan and protozoan parasites but their exposure to viral and bacterial pathogens is unknown. We tested for herpes viral DNA in leucocytes and found that 21 of 42 tested sheep were infected with ovine herpesvirus 2 (OHV-2). We also tested 750 plasma samples collected between 1997 and 2010 for evidence of exposure to seven other viral and bacterial agents common in domestic Scottish sheep. We found evidence of exposure to Leptospira spp., with overall seroprevalence of 6·5%. However, serological evidence indicated that the population had not been exposed to border disease, parainfluenza, maedi-visna, or orf viruses, nor to Chlamydia abortus. Some sheep tested positive for antibodies against Mycobacterium avium subsp. paratuberculosis (MAP) but, in the absence of retrospective faecal samples, the presence of this infection could not be confirmed. The roles of importation, the pathogen-host interaction, nematode co-infection and local transmission warrant future investigation, to elucidate the transmission ecology and fitness effects of the few viral and bacterial pathogens on Hirta.

Contamination and compensation: Gruinard as a 'menace to the mainland'.

The decades-long contamination of Gruinard Island by anthrax is now a well-known part of the history of biological weapons (BW) development, as well as that of military encroachments in the Scottish Highlands and Islands (and the authorities' rather less persistent efforts at damage limitation). Some accounts have included the related episode, reportedly well-remembered by local people, of anthrax contamination on the mainland close to Gruinard. This occurred in 1942--43, when BW experiments were conducted on the island as part of the war effort by scientists from Porton Down under the auspices of the British government. After much top-level discussion, payments were made to the owners of animals that had died as a result of the contamination. The episode had a bearing on discussions about the future of the island and on subsequent policy with regard to the siting, conduct and secrecy of BW experiments.

Infectious disease mortality in two Outer Hebridean islands: 1. measles, pertussis and influenza.

OBJECTIVES: The purpose of the study was to examine changes in mortality from measles, pertussis (whooping cough) and influenza (all epidemic diseases) in Harris and Barra, two Outer Hebridean islands, from 1855 to 1990, and to compare the findings with those from Scotland as a whole over the same period. It was also intended to relate changes in mortality to those in social and economic factors. MATERIALS AND METHODS: Ages and causes of death in Harris and Barra were ascertained from copies of death certificates held at the General Register Office, Edinburgh, and for Scotland as a whole from the Annual Reports of the Registrars General for Scotland. Data were standardized by calculating the Proportionate Mortality Ratio (PMR), the proportion of deaths due to a particular cause to all deaths over a given period. Spectral analysis was employed to examine the durations of epidemic cycles. RESULTS: Ages at death increased slightly over the period of the study. For measles and pertussis, other than for the former in Harris, there were significant relationships between numbers of deaths per decade, and numbers of new susceptibles, estimated as the numbers of births. Epidemics of measles and pertussis in the islands occurred at intervals, usually separated by years of no mortality. The highest PMRs were generally during the later decades of the 19th and first decade of the 20th centuries; this may have been related to the economic problems of agriculture and fishing, and to increasing population density. Influenza epidemics were more frequent than those of the other two diseases. For all three diseases in both islands, there were significant negative power relationships between epidemic size and frequency of occurrence; those in Harris were the stronger. The relationships between length and frequency were significant only in Harris. Generally, epidemic lengths seemed less variable than sizes, possibly because of the rather 'coarse' units of length (quarters) employed. Spectral analysis of the 'detrended' data for the period before the introduction of specific immunoprophylaxis revealed that for measles the main epidemic cycle in all three populations was between 7.3 and 7.8 years' duration. Barra and Scotland had additional 2.5- and 2-year cycles, respectively. For pertussis, Harris and Barra had main cycles of 7.4 years. Harris had an additional cycle of 3.2 years. Scotland had cycles of 4 and 2 years. For influenza, Harris had a main cycle length of 7.4 years, and a less-defined one of about 2.6 years. Barra had a main cycle of 6.9 years, and a subsidiary one of 2 years. Scotland has a single cycle of 8 years. Cubic regressions of the spectral densities on cycle frequencies showed large coefficients for Harris and Barra, but small ones for Scotland. Measles coefficients were closely similar in the two islands, but not those for pertussis. CONCLUSIONS: The findings demonstrate the episodic occurrence of epidemics of these three diseases in the two islands, as against their continual presence in the much larger population of Scotland. They reveal also the decreasing importance of these causes of death in all three populations. The data from Harris and Barra suggest that measles is a more epidemiologically 'stable' disease than pertussis. Both islands appear to obey Hamer's law of 'mass action'. The relatively long intervals between epidemics in the islands may be due partly to their isolation, and partly to the slow accumulation of sufficient numbers of susceptibles to enable an epidemic to occur.

Infectious disease mortality in two Outer Hebridean islands: 2. pulmonary tuberculosis.

OBJECTIVE: To examine mortality from pulmonary tuberculosis (PTB) in the Outer Hebridean islands of Harris and Barra, and to compare it with that in Scotland as a whole. DESIGN: Ages and dates of death from PTB in Harris and Barra between 1855 and 1990 were ascertained from copies of death certificates. For Scotland, annual numbers of deaths in 5-year age-groups were extracted from Annual Reports of the Registrars General. Proportionate mortality ratios (PMRs) were calculated for each population in the 1-14 and 15 or over age-groups, and the 'detrended' PMRs were subjected to spectral analysis. For this purpose the data were divided into the pre-antibiotic (1855-1950) and antibiotic/chemo-therapeutic (1951-1990) periods. RESULTS: PTB was predominantly a disease of adolescence and early adulthood, although ages at death increased towards the end of the period of study. While PMRs for Scotland decreased steadily after the mid-1870s, apart from increases during the 1940s, those for the two islands increased during the late 19th century, and did not decrease markedly until the 1930s. In the younger age-groups the pattern of mortality was similar to that of an acute infectious disease, while in the older age-group the pattern was largely endemic. Spectral analysis of pre-1951 data from both islands showed marked periodicities in mortality, mostly among the younger age-group. The introduction of effective therapy in the 1950s appeared to lengthen inter-epidemic intervals. There appeared to be no relationship in either island between mortality and socio-economic deprivation, as indicated by numbers of new poor registrations. In Harris, mortality was higher in colder and wetter years. This was not the case in Barra. CONCLUSIONS: The findings are reasonably consistent with a hypothesis that PTB was relatively uncommon in the Outer Hebrides until the later 19th century, and that it behaved epidemiologically like an acute infectious disease. This was not the case with Scotland as a whole, where the disease appeared to be largely endemic.

Nursing at the edge of the world: nurses on St Kilda.

In the early twenty-first century geographically isolated communities continue to experience unequal access to health care. The advent of new technologies such as telemedicine do not overcome the financial constraints of employing professionals such as health visitors or district nurses to meet the needs of these remote areas. In late nineteenth century Britain there were few more isolated communities than the St Kildans. Although it is 70 years since St Kilda was evacuated it continues to capture the popular imagination. This archipelago of islands lies less than 50 miles west of the Outer Hebrides yet remains inaccessible by sea except on the calmest of summer days. Isolation such as this may have been acceptable, even desirable, to the islanders for generations but became problematic with their increasing reliance on supply boats for food. As the population dwindled it became more difficult to be self-sufficient, with few able-bodied men to row to the nearby rocks and climb to harvest the seabirds that were their staple diet. The rocks, or stacs, as they are known, have sheer cliff faces rising spectacularly from the sea. It would be logical to assume that the population had difficulty expanding due to the high male mortality rate from accidents on the these pinnacles. But it was not the skillful rock climbers that were dying in large numbers, it was their babies. Sustained infant mortality rates of between 50-70 per cent during the nineteenth century contributed to the consistently low population levels which led to the eventual death of the community. It is surprising in this context to learn that the first nurses to serve the St Kildans were ostracised and rejected by the islanders.

Religion and fertility in the Outer Hebrides.

Estimates of fertility in Protestant Barra and Catholic Harris, islands in the Outer Hebrides, over the period 1856-1985, show that in both islands fertility declined, although marital fertility was generally greater than in Scotland as a whole, and illegitimate fertility was less. However, in Barra during 1966-75 there were pronounced rises in all the indices; illegitimate fertility showed the smallest rise. The publication of the papal encyclical Humanae Vitae may have played a part in this change in fertility, although other, probably local, factors must have been acting, as the first rise in numbers of births occurred before the publication of the encyclical. Other than this transient rise, the religious difference between Harris and Barra had little effect on changes in fertility over the whole period. Indices of proportions married showed declines until after World War 2, followed by steep increases. The marked decline in fertility in both islands may be due in part to this low nuptiality. In addition, a trend of occupation away from traditional crofting and fishing towards more skilled mercantile and professional employment may have played a role.

PIP: Fertility-related data from 1855-1985 were analyzed to compare estimates of fertility in the most southern island of the Outer Hebrides, Barra, with those of an area of the most northern island called Harris. The predominate religion in Barra was Protestant and that in Harris was Catholic. The latter part of the 19th century and/or early 20th century witnessed an increased growth in the numbers of children aged 0-4 years (1916-1925 for Harris and 1896-1905 for Barra), of women in the reproductive period of life (peaking in 1901 for Harris and in 1922 for Barra), and in number of births per decade (1861-1901 for Harris and Barra). Thereafter, these numbers fell consistently in both islands until relatively recently. Marital fertility tended to be higher and illegitimate fertility tended to be lower in both islands than in Scotland as a whole. In Barra during 1966-1975, marked increases in all indices occurred (e.g., total fertility = 0.430 vs. 0.210 in 1956-1965 and 0.167 in 1976-1985). Illegitimate fertility increased the least (0.016-0.110). The release of the 1968 papal encyclical Humanae Vitae reaffirming the strong traditional Catholic attitudes towards family limitation, may have contributed to this temporary rise in fertility. Further examination suggests that it may have played a limited role, since the first increase in numbers of births took place before its publication. Thus, other, probably local, factors may have accounted for this rise. Overall, the religious difference between Harris and Barra contributed (at most) little changes in fertility, other than the transient increase. The proportions of married couples fell considerably over the years until after World War II at which time they increased greatly (e.g., prior to 1936 in Harris, 0.371-0.323, 1936-1945 and after 0.346 and 0.369-0.539, peaking in 1966-1975 at 0.702). This low nuptiality may have accounted for some of the strong decline in fertility in both islands. The shift from the occupation of traditional crofting and fishing to more skilled mercantile and professional employment may have also contributed to this decline.

Aspects of neonatal death in St Kilda, 1830-1930.

Neonatal death (mainly due to tetanus) was common in St Kilda until 1891. Two aspects of this phenomenon are studied; factors which predicted death, and the impact of neonatal death on family building. Maternal age appeared to be a predictive factor for death of the first child, but only in children of high birth order were other factors, particularly the number of previous neonatal deaths, important. The first birth interval appeared to be determined mainly by the date of the first birth, independent of neonatal mortality levels. For later intervals, the neonatal death of the previous child appeared to be the main determining factor.

PIP: Two researchers analyze vital event records and parish registers to identify determinants of neonatal mortality and the effect neonatal death had on family building during 1830-1930 in St. Kilda, the most remote island of the Outer Hebrides off the northwest coast of Scotland. Before 1892, more than 50% of the infants born on St. Kilda died from neonatal tetanus (8-day sickness). Even though various sponsors sent nurses to St. Kilda to introduce antiseptic delivery techniques, the islanders did not accept these techniques until the minister became a man-midwife. The total number of known births during the period was 176. 1891-1892 also experienced a major change in the distribution of neonatal deaths by birth order. Before 1892, neonatal death was more common among early and late birth orders, while, after 1892, birth order appeared not to be related to risk of early neonatal mortality. Neonatal death could be predicted rather reliably for the first birth, but not the second or third births. Age at marriage for first births, maternal age at birth and the number of previous neonatal deaths for all birth orders, and the preceding birth interval for fifth births were significant predictors of neonatal death. The date of the first birth, regardless of neonatal mortality levels, determined the first birth interval. As for later birth intervals, the neonatal death of the previous child was the leading determinant of neonatal death.

Epidemiology of nematode infections of Soay sheep (Ovis aries L.) on St Kilda.

The epidemiology of nematode infections of Soay sheep on the island of St Kilda over a period of 2 years (August 1988-August 1990) spanning a host population crash is described. Infective larvae (L3) levels on pasture were high (2422 +/- 365 L3/kg D.M. grass in midsummer 1988) when host population density was high, decreasing after the sheep population declined by 70% in early 1989 (601 +/- 14 L3/kg D.M. in midsummer 1989). The availability of infective larvae to sheep increased during the winter of 1988-1989, probably as a result of concentration of existing larvae on grass as vegetation was destroyed by bad weather and overgrazing. Increased availability of pre-parasitic stages was accompanied by a marked increased in faecal egg counts from sheep of all ages and both sexes. Prevalence and intensity of infection (faecal egg counts) were higher in males than females throughout the 2-year study (chi 2 = 208.3, P < 0.005 and F1, 2000 = 304, P < 0.001 respectively), except during the lambing periods, and decreased with age in both sexes. Changes in prevalence and intensity of strongyle infections were associated with changes in host population density. Prevalence and intensity of Dictyocaulus filaria larvae in faeces increased during the host population crash. Infection intensity decreased with age (F1, 203 = 44.02, P < 0.001) and was higher in males than females (F1, 203 = 13.45, P < 0.001).