Finding causes of seasonal diseases using time series analysis

The relationship between monthly Ischaemic Heart Disease mortality and mean monthly temperature and rainfall is examined using data for England and Wales covering the period 1968 to 1976. The statistical procedure adopted involves a time series analysis of each of the individual series employing an approach which has become increasingly popular in other sciences over the last decade. Results indicate the correlation coefficients quoted in previous studies involving monthly data are spuriously high implying that temperature is not as closely related to Ischaemic Heart Disease deaths as has often been claimed.

Climate and anthropometric variations in Europe and the Mediterranean area

Fourteen anthropometric measurements collected among 85 European, North African and Middle Eastern populations have been studied with respect to eight climatic variables through zero-order correlations and multiple stepwise regressions. The average contribution of climate to the total variance of physical features between populations is 35%. The most important correlations of postcranial body measurements and nasal index are with the extremes of heat and dryness, while the head measurements are more sensitive to extremes of cold and moisture. The overall results indicate that these populations follow the zoological rules of Bergmann and Allen.

Weather and infectious disease in cattle

The incidence and severity of many diseases of cattle, particularly the endemic enteric and respiratory diseases, appear from clinical impression or epidemiological survey to be associated with particular types of weather. Infectious diseases of cattle (excluding parasitic ones) for which there appears to be a real association between climate, weather and disease are reviewed. Effects of weather on survival and spread of microorganisms, local resistance to infection and systemic resistance to disease are discussed. Factors such as cold, heat, relative humidity and air pollution are considered with particular reference to the aetiology of respiratory diseases.

Regulation of seasonal occurrence in the tick Rhipicephalus appendiculatus Neumann, 1901

Published data on the seasonal occurrence of Rhipicephalus appendiculatus at 8 localities in east, central and southern Africa has been compared and an analysis of the regulatory roles of different climatic factors has been undertaken. It has been shown that the pattern of seasonal occurrence is largely dependent on the timing of the activity period of the adult stage and this is regulated by the combined influences of humidity, temperatures and daylength. By use of a simple model it is shown how the adult activity period in a given climatic regimen can be predicted on the basis of easily obtainable meteorological data. The value of the model in planning tick and disease control programmes is discussed.

The seasonal activity of Rhipicephalus appendiculatus Neumann 1901 (Acarina: Ixodidae) in the highveld of Zimbabwe Rhodesia

Rhipicephalus appendiculatus passes through one generation per annum in the highveld of Zimbabwe, Rhodesia and shows a well-defined pattern of seasonal activity. Peak adult activity occurs in the rainy season, whereas peak larval and nymphal activity occurs in the dry season. Adult activity is regulated by the combined influences of temperature, humidity, and day length. Climatic factors have little or no direct influence on the activity of larvae and nymphs. The occurrence of the larval and nymphal activity peaks is determined by the timing of the adult activity peak and the duration of the preceeding developmental periods, which are temperature dependent. In the early rainy season, unfed adults climb to the tips of the grass and enter a period of quiescence prior to becoming active.

[Role of climatic and geophysical environmental factors in synchronizing seasonal variations in the activity of body's nonspecific mechanisms of defense against infection]

The method of multifactor dispersion analysis was used to reveal that the synchronizing effect resulting from the action of the complex of climatic and geophysical environmental factors (day length, barometric pressure, magnetic field perturbations) on the non-specific mechanisms of protection from infections during the year exceeded the results obtained by the mere summation of the influences contributed by each factor. Therefore, the seasonal fluctuations in the functions of the nonspecific resistance of the body against infection were due to the synchronizing action of the complex of geophysical factors changing with the seasons.

Frequency of airborne Alternaria spores in Tucson, Arizona over a 20-year period

Once recommended by clinicians to the allergy sufferer as a refuge due to its healthful arid climate, Tucson is now noted for its incidence of asthma which if two to three times higher than the nation as a whole. This increase in asthma incidence has been attributed in part to a 10-fold increase in atmospheric pollen over the years due to the widespread use of high pollen-producing shade and ornamental trees. Data obtained by Durham slide sampler also reveal a five-to-tenfold increase in numbers of Alternaria (Alt) spores in Tucson over the last 20 years. This may be linked to the increasing numbers of certain pollen producing plants which may serve as the substrate for the mold. Relationships appear to exist between Alternaria frequency and numerous climatic conditions such as precipitation, average monthly relative humidity, average monthly temperature and incident radiation. Because of these relationships the frequency of Alternaria may be predictable on a daily, seasonal and yearly basis.

Energy expenditure of male farmers in dry and rainy seasons in Upper-Volta

1. Thirty Mossi male farmers from Upper-Volta were investigated, twenty-three in the dry season (March-April) and sixteen in the rainy season (July-August), eight of them being studied twice. A 48 h time-and-motion study was carried out and the daily energy expenditure was computed. 2. The mean height was 1.70 m and the mean weight 58.5 kg. The averaged percentage of body fat calculated from skinfold thickness was 10. 3. During the dry season the subjects could be classified as very moderately active with an energy output of 10.0 MJ (2410 kcal)/d. By contrast, with an energy expenditure of 14.4 MJ (3460 kcal)/d, they were considered as exceptionally active in July-August when performing the agricultural work. 4. In this study we measured the intensity of physical work in a society where human labour is still the main tool of production. The determination of seasonal variations in energy expenditure may be useful to assess the nutritional requirements in arid zones of West Africa.

[Biological control of Lymnaea truncatula Müller in Haute-Vienne, France. Apropos of several factors limiting its application]

The author analyzes the positive and negative results of a year of biological control by predation on 49 stations of Lymnaea truncatula in Haute-Vienne, France. The negative results can be explained by the effects of 6 natural factors: 1--the rainfall over the habitats during the first 10 days of the experimentation. The rate of natural mortality and predation of L. truncatula is reduced at values above 8 mm rainfall. The predatory snails leave the sodden soil and do not consume L. truncatula; 2--the presence of stone blocks on the habitat. These blocks constitute shelters for L. truncatula; 3--the quality of the plant cover. Rushes and graminaceae preferentially must be used; 4--the previous treatment of the habitat by a molluscicide (copper sulphate) just before the application of biological control. The predators preferentially consume the more poisoned L. truncatula and forsake the more healthy snails; 5--the presence of phoretic acaridae on the predators which die; 6--the behaviour of sheep on the habitats situated on pastures with steep slopes. Their repeated passages cause the squashing of the predators. The proposed solutions are discussed in the limits of the region of experimentation.

The persistence and disappearance by washoff and dryfall of methoxychlor from soybean foliage--a preliminary study

The persistence and disappearance (washoff or dryfall) of methoxychlor [2,2-bis(p-methoxyphenyl)-1,1,1-trichloroethane] from mature soybean [Glycine max (L.) Merrill] foliage was investigated in a small field plot study under natural rainfall conditions in 1977 and 1978. Residue analyses were conducted using whole plant samples. Methoxychlor washoff rate was 8+/- 4% of the amount on plants (prior to rain) per centimeter of rainfall, regardless of time after application. Total seasonal washoff for 1978 accounted for 33.5% of the applied pesticide; however, 30.5% of the total loss was removed by washoff on the second day after application. Dryfall or dislodgeable residue accounted for less than 1% of the amount applied. The amount of dryfall was significantly greater in plots entered by workers than in those where entry was avoided. More than 19% of the applied methoxychlor was lost as a result of through-fall to the ground during application to the plots. Statistical analyses indicated that within-sample variation for mechanical chopping of plant samples was significantly smaller at the 5% level than for a hand chopping method. Results from this study will be useful in defining research objectives for the development of algorithms to describe the behavior of foliar-applied compounds. Such algorithms are necessary for estimating runoff losses of insecticides to water bodies.

Causes of variation between months in the distance traveled daily of gibbons

The monthly medians of the distances traveled daily by siamang and lar gibbons are negatively correlated with rainfall and positively correlated with the separate and combined abundance of different food categories. The latter correlations indicate that the apes follow a policy of cutting their losses by reducing travel when food abundance falls.

Local differences in responses to water among wild chimpanzees

Behaviors in relation with water are described in detail for wild chimpanzees of the Manhale Mountains, Tanzania: drinking, wading streams, feeding, responses to rain, etc. When the results are compared with those of Gombe National Park, some behavioral differences emerge: drinking directly from the lake, feeding on aquatic plants, back/shoulder rubbing behavior by making day-beds, etc. are observed only for chimpanzees of the Mahale Mountains, while sponging to obtain water is observed only for those of Gombe. These may be examples of "tradition drift' in wild chimpanzees. Moreover, it is suggested that there is no innate hydrophobia among any of the African great apes.

Poliovirus retention in 75-cm soil cores after sewage and rainwater application

The adsorption rate of a guanidine-resistant strain of poliovirus LSc 2ab was measured in Long Island soils with in situ field cores (10.1 by 75 cm). The test virus was chosen because it exhibited soil adsorption and elution characteristics of a number of non-polioviruses. After the inoculation of cores with seeded sewage effluent at a 1-cm/h infiltration rate, cores were extracted, fractionated, and analyzed for total plaque-forming units per each 5-cm fraction. The results showed that 77% of the viruses were adsorbed in the first 5 cm of soil. An additional 11% were found in the 5- to 10-cm fraction, and a total of 96% of the viruses were adsorbed by 25 cm. The remaining 4% were uniformly distributed over the next 50 cm of soil, with a minimum of 0.23% in each soil section. Few viruses (< 0.22%) were observed in core filtrates. Analysis of the viral distribution pattern in seeded cores, after an application of a single rinse of either sewage effluent or rainwater, indicated that large-scale viral mobilization was absent. However, localized areas of viral movement were noted in both of the rinsed cores, with the rainwater-rinsed cores exhibiting more expensive movement. All mobilized viruses were resorbed at lower core depths.

Seasonal size variation in females of the Simulium damnosum complex in the Ivory Coast

The thorax lengths of monthly samples of female S. damnosum s.l. caught between August 1975 and February 1977 at Danagoro in the Ivory Coast were measured. The blackflies could be separated into three species groups according to their external characters. Flies attributable to S. damnosum/S. sirbanum and S. soubrense/S. sanctipauli were common. S. yahense was occasionally found. The flies of the S. soubrense/S. sanctipauli group were on average consistently larger than those of the S. damnosum/S. sirbanum group within any one month. The mean sizes of these two groups varied in parallel from month to month and this variation was related to the rainfall in and around the drainage basin. This relation is discussed with respect to possible changes in the discharges of local rivers and their effects on larval development.

Interactions and survival of enteric viruses in soil materials

There were marked differences in the abilities of eight different soil materials to remove and retain viruses from settled sewage, but for each soil material the behavior of two different viruses, poliovirus type 1 and reovirus type 3, was often similar. Virus adsorption to soil materials was rapid, the majority occurring within 15 min. Clayey materials efficiently adsorbed both viruses from wastewater over a range of pH and total dissolved solids levels. Sands and organic soil materials were comparatively poor adsorbents, but in some cases their ability to adsorb viruses increased at low pH and with the addition of total dissolved solids or divalent cations. Viruses in suspensions of soil material in settled sewage survived for considerable time periods, despite microbial activity. In some cases virus survival was prolonged in suspensions of soil materials compared to soil-free controls. Although sandy and organic soil materials were poor virus adsorbents when suspended in wastewater, they gave >/=95% virus removal from intermittently applied wastewater as unsaturated, 10-cm-deep columns. However, considerable quantities of the retained viruses were washed from the columns by simulated rainfall. Under the same conditions, clayey soil material removed >/=99.9995% of the viruses from applied wastewater, and none were washed from the columns by simulated rainfall.

Seasonality in human hookworm infection in an endemic area of Nigeria, and its relationship to rainfall

Detailed parasitological and climatological examination of two rural communities in a hookworm endemic area of Anambra State Nigeria, has shown that infection with the parasite follows a clearly defined pattern. The results suggested a break in the transmission cycle of the parasite during the dry season December--February when only a few larvae (< 500 L3S) could be recovered from contaminated soils for not more than 4 days. Transmission of the parasite and the manifestation of the disease in infected individuals appeared to be a rainy season phenomenon. The implications of these findings are discussed in relation to possible control of the disease.

Performance of adhesives for rotating-arm impactors

Particle collections by paired rotoslide surfaces coated differentially with either of two silicone greases, white petrolatum or Lubriseal, were compared in two series of studies. Three samplers were employed, and adhesives were assigned randomly to the six available positions. Recovery differences were small but occasionally significant, with counts generally highest for silicone grease and lower with Lubriseal. During natural and simulated rainfall relative performances were similar, although differences were accentuated.

British Regional Heart Study: geographic variations in cardiovascular mortality, and the role of water quality

In a study of regional variations in cardiovascular mortality in Great Britain during 1969-73 based on 253 towns the possible contributions of drinking water quality, climate, air pollution, blood groups, and socioeconomic factors were evaluated. A twofold range in mortality from stroke and ischaemic heart disease was apparent, the highest mortality being in the west of Scotland and the lowest in south-east England. A multifactorial approach identified five principal factors that substantially explained this geographic variation in cardiovascular mortality-namely, water hardness, rainfall, temperature, and two social factors (percentage of manual workers and car ownership). After adjustment for other factors cardiovascular mortality in areas with very soft water, around 0.25 mmol/l (calcium carbonate equivalent 25 mg/l), was estimated to be 10-15% higher than that in areas with medium-hard water, around 1.7 mmol/l (170 mg/l), while any further increase in hardness beyond 1.7 mmol/l did not additionally lower cardiovascular mortality.Thus a negative relation existed between water hardness and cardiovascular mortality, although climate and socioeconomic conditions also appeared to be important influences. Cross-sectional and prospective surveys of 7500 middle-aged men from 24 towns are in progress and will permit further exploration of these geographic differences, especially with regard to personal risk factors such as blood pressure, blood lipid concentrations, and cigarette smoking.

Movement of endotoxin through soil columns

Land treatment of wastewater is an attractive alternative to conventional sewage treatment systems and is gaining widespread acceptance. Although land application systems prevent surface water pollution and augment the available water supplies, the potential dangers to human health should be evaluated. Since sewage may contain high amounts of bacterial endotoxin, the removal of endotoxin from sewage by percolation through soil was investigated. It was found that 90 to 99% of the endotoxin was removed after travel of sewage through 100 to 250 cm of loamy sand soil. When distilled water was allowed to infiltrate into the soil to simulate rainfall, the endotoxin was mobilized and moved in a concentrated band through the soil column. On testing samples from actual land treatment sites, as much as 480 ng of endotoxin per milliliter was found in some groundwater samples. The presence of endotoxin in potable water is known to be a potential problem under some circumstances, but the importance of endotoxin in water supplies has not been fully assessed. Therefore, the design, operation, and management of land application systems should take into account the fate of endotoxin in groundwater beneath the sites.

Aerobiological studies based in Galway. A comparison of pollen and spore counts over two seasons of widely differing weather conditions

A comparison was made of the pollen and spore counts at Galway in relation to the varying weather conditions of the summers of 1977 and 1978 in an attempt to explain the low incidence of allergies in that area during the summer of 1978. The phenomenon was attributed to the change in the dominant wind direction, which, from May to September 1978 was mainly over sea. Correlations were made between changes in pollen and spore catches and variations in particular meteorological factors for both seasons investigated.

Some observations on the incidence of lameness in dairy cattle in Somerset

A three year study of practice records of lame cows and meteorological data on rainfall suggests a correlation between rainfall and incidence of lameness in dairy cattle. Over a 12 month period requests to treat lameness in 1256 cattle were received by one six-person practice and were the subject of a detailed survey. The incidence on the 150 farms where lameness was recorded was 7.33 per cent, 92.2 per cent of lameness occurring in the foot. White line disease (34.9 per cent), pricked sole (20.4 per cent), foul in the foot (14.3 per cent) ulcerated sole (11.4 per cent), and foreign body (4.8 per cent) accounted for 85.8 per cent of the 927 recorded foot lesions. Hind feet lameness appeared more common in older cows, but this was not shown to be the case with front foot lameness. Lameness also appeared to be most common in early lactation and of relatively low incidence in the dry period. The seasonal distribution differed between the lesions, ulcerated sole being more common February to May, foul in the foot and white line separation in the autumn, and white line abscess and pricked sole in the autumn and winter months.

Organic contaminates in water

The carbon adsorption method was used for separating organic matter from large samples of drainage, river and tap water. The carbon chloroform extract (CCE) was separated into different solubility fractions and the neutral fraction was separated into aliphatic, aromatic and oxy-compounds using column chromatography. The aromatic fraction was subjected to TLC, IR and UV analysis. The pesticide endrin was present in both river and tap water at concentrations of 0.7 and 1.5 ppb, respectively.

Isolation of the Mycobacterium avium-M. intracellulare-M. scrofulaceum complex from tank water in Queensland, Australia

Disease-associated serotypes of Mycobacterium intracellulare and M. avium have been isolated from 32 of 141 rainwater tanks situated in the basin of the Fitzroy River and its tributaries in central Queensland, 7 of 32 tanks situated in the hinterland of the coastal city of Rockhampton, and 2 of 32 tanks sampled repetitively in the southeastern Queensland city of Toowoomba. M. gordonae was also isolated from 23 of the river basin tanks, from 9 in the Rockhampton hinterland, and from 5 in the city of Toowoomba. One half of these isolates came from tanks which also yielded M. intracellulare. Mycobacteria of the M. terrae-M. triviale-M. nonchromogenicum complex were found in 7 tanks, usually in conjunction with M. intracellulare. The humans who consume the contaminated tank water are free of symptoms but have not been medically examined. It is suggested that mycobacteria adhering to dust particles disturbed by mechanical cultivation may be the source of contamination.

Necator americanus: population structure, distribution, and fluctuations in population densities of infective larvae in contaminated farmlands

Observations have been made over a 15-month period on the frequency distribution of human faecal deposits and infective larvae of Necator americanus in a hookworm endemic area. The agestructure of infective larvae in a field population and their vertical distribution in soils were determined. These studies were undertaken to examine the hypothesis that hookworm transmission in the tropics is discontinuous and limited mainly to the rainy season. The distribution of larvae was found to be overdispersed statistically and in general much greater numbers of L3s were recovered during the rainy season. The degree of overdispersion was also reduced during this season, and there was a tendency for larvae to be confined to the surface/topsoil. The implications of these findings have been discussed in relation to human hookworm parasitism in endemic areas of the tropics.

The use of time and space by the Panamanian tamarin, Saguinus oedipus

Tamarin activity patterns and habitat utilization strategies in the Tropical Dry Forest of the Panama Canal Zone were monitored quantitatively using radio-location telemetry. The daily tamarin activity pattern differed from that of other Neotropical primates in that early morning and late afternoon activity normally did not occur. Total daily activity time averaged 676 +/- 62 min. Sleeping trees, and behaviors associated with their use, were documented. Daily path length averaged 2,061 +/- 402 m. Mean travel distance was 468 +/- 66 m. Approximately one-third of the home range was utilized on a given day. Wet season home ranges for two social groups were 26 and 32 ha in area. Areas of low brush, forest edge, and vine-entangled second growth were heavily used by foraging tamarins. Large shade trees, particularly evergreens, were important as refuges from solar radiation. Open-canopy forest types and areas of grass were avoided. Social groups on resource-stable lowland sites defended territories; those on unstable upland sites used a system of time-space segregation. Upland groups became seminomadic during the dry season. Suitability of home range site may affect social group stability, natality, and infant survivorship.

Incidence of fungal spores at the homes of allergic patients in an agricultural community. III. Associations with local crops

A predominantly agricultural community in California was surveyed for prevalent fungal spores during a 12-month period. Alternaria, Macrosporium and Stemphylium were recovered during asparagus and strawberry harvesting times year-round. Fusarium and Botrytis were less frequently associated with the strawberry harvest and were recovered only during the first quarter of the year. Epicoccum was recovered in the north end of the Salinas valley in low numbers throughout the year and was strongly associated with the strawberry and artichoke harvest. Aureobasidium (Pullularia) recovery occurred in different locations according to season, correlating somewhat with the cabbage harvest as well as with the harvest of strawberries. Recovery of the pigmented yeats showed strong correlation with the local growing season for lettuce. Cladosporium was prevalent year-round but did not appear to be signficantly affected by changing argicultural conditions. These data have permitted the predictability of mold aeroallergens with medical applications.

Effect of additions of liquid poultry manure on excretion of degradative enzymes by bacteria in forest soil and litter

Liquid poultry manure was applied to three forest sites at 35, 70, and 225 metric tonnes (1 tonne = 1000 kg) per hectare (1 ha = 10 000 m2) for 1 to 3 years. Two of the sites were white pine plantations, one dry, one moist, and the third site was mixed hardwoods. Over a period of 35 months the total bacterial population in litter and in soil, in both control and manure plots, was studied as well as the ability of the population to produce extracellular proteases, cellulases, lipases, pectinases, and amylases. Total bacterial counts in litter tended to be higher in the autumn and lower in the spring. Litter always contained about 10-fold more bacteria than soil and the number of bacteria in soil fluctuated little with season or treatment. In white pine litter, bacteria able to excrete protease were more numerous than other enzyme-producing bacteria. More bacteria able to excrete lipases were found on moist than on dry sites, especially on manured plots. At the end of the 35-month test period, all bacterial counts in manured plots had returned nearly to the original level of the control. Statistical analysis revealed significant differences in total bacterial count and counts of specific enzyme producers between manured and control plots. Little difference was seen among rates of manure application. Adding large amounts of poultry manure to these forest plots did not greatly change the bacterial ecology of the soil or litter.

An Australia-wide outbreak of gastroenteritis from oysters caused by Norwalk virus

At least 2000 persons were involved in an Australia-wide outbreak of oyster-associated food poisoning in June and July, 1978. At the time, this episode presented a major health risk to the community as a whole and has subsequently posed a serious economic problem for the oyster farming and distributing industry. Although bacteriological investigations indicated some batches of oysters were contaminated by sewage, no bacterial cause could be established. The causative organism was shown to be Norwalk virus, a known cause of acute non-bacterial gastroenteritis. This virus was found in 39% of faecal specimens examined by electron microscopy and an antibody response was demonstrated by immune electron microscopy in 75% of paired sera tested. Norwalk virus has not been identified previously outside the United States of America and has not been linked to food-borne gastroenteritis before. Purification of oysters and other measures have been instituted to prevent a recurrence of the outbreak.

Adsorption of enteroviruses to soil cores and their subsequent elution by artificial rainwater

The adsorption and elution of a variety of human enteroviruses in a highly permeable, sandy soil was studied by using cores (43 by 125 mm) collected from an operating recharge basin on Long Island. Viruses studied included field and reference strains of polioviruses types 1 and 3 and reference strains of coxsackie virus B3 and echovirus types 1 and 6. Viruses suspended in treated sewage effluent were allowed to percolate through soil cores, and the filtrate was assayed for unadsorbed viruses. To determine the likelihood of desorption and mobilization, soil-bound viruses were subjected to a rinse with either treated sewage effluent or simulated rainwater which reflected the anion, cation, and pH characteristics of a typical northeastern United States rainfall. The results demonstrated that all polioviruses tested, including both reference and field strains, adsorbed extremely well to cores. Adsorption was somewhat reduced when clean, unconditioned soils were used. Soil-bound poliovirus strain LSc was not significantly mobilized by flooding columns with either a sewage effluent or rainwater rinse. One virus was mobilized by both types of rinses. The amount of viruses mobilized by rainwater rinses ranged from 24 to 66%. Variable adsorption-elution results were observed with other enteroviruses. Two guanidine-resistant mutants of poliovirus LSc demonstrated a soil adsorption-elution profile different from that of the parent strain. The data support the conclusion that soil adsorption-elution behavior is strain dependent and that poliovirus, particularly strain LSc, represents an inappropriate model.

The epidemiology of ringworm in racehorses caused by Trichophyton equinum var autotrophicum

The epidemiology of dermatomycocis due to Trichophyton equinum var autotrophicum was studied in a number of thoroughbred stables in south-east Queensland. The significant factors in the epidemiology were defined. The infection was readily transmitted, particularly by infected saddle-girths, on which the fungus could survive for 12 months. Mild abrasion from the saddle during work favoured the development of lesions and prolonged the recovery period. A pronounced age and seasonal incidence of the disease was demonstrated as young horses under the age of 3 years were most susceptible, and the majority of cases occurred in periods of high humidity.

Racial and environmental factors in acute haematogenous osteomyelitis in New Zealand

Data on the hospital incidence of acute haematogenous osteomyelitis in New Zealand children between 1965 and 1973 are presented. The incidence in Maori children is four times that in European children. The condition is more common in the North Island than the South Island, but this difference is mainly due to the distribution of the Maori people. Admissions to hospital are common in late summer and autumn. The relationship of osteomyelitis to skin and ear sepsis and some possible reasons for ethnic difference, are discussed.

The relationship between rainfall and well water pollution in a West African (Gambian) village

Water pollution was monitored in six Gambian village wells over a period of 8 months spanning the 5-month monomodal rains and the pre- and post-rains dry periods. Faecal coliform (FC) and faecal streptococci (FS) counts were high throughout and there was a massive increase associated with the onset of the rains, maximum counts exceeding 5 x 10(5)/100 ml. This pattern was largely sustained throughout the rainy season. Some individual variations in patterns of pollution could be ascribed to well design, in particular lining of the shaft, but no well was protected from the seasonal increase in faecal pollution. The source of the increased pollution appeared to be a flushing in of faecal material of indeterminate or mixed human and animal origin, probably over considerable distances. Peaks of pollution not associated with rainfall episodes could have resulted from the practice of communal laundering in the near vicinity of the wells. Specific pathogens including Salmonella spp. were isolated only intermittently. Attention has been drawn to a problem complicating the standard method for assessing FC counts.

Studies on the epidemiology of trypanosomiasis in sheep and goats in Kenya

The epidemiology of trypanosomiasis in a tsetse-infested range area of Kenya was studied for 2 years in various breeds of sheep and goats. Observations, including infection rates, PCV, temperature and weight loss indicated that the exotic breeds were more susceptible to natural trypanosomal infection than the indigenous breeds and that the infection may be severely debilitating and in many cases fatal. Observations of tsetse numbers and rainfall in the grazing area during the first year showed that there was a significant correlation between tsetse numbers and rainfall of the previous month. The increase in tsetse numbers, which occurred one month after substantial rainfall, was followed by an increase in the prevalence of trypanosomiasis in the animals. However, during the second year when rainfall was low there was no correlation between tsetse numbers and rainfall. It was concluded that the seasonal incidence of trypanosomiasis and the possible trypanotolerance of the indigenous breeds are important factors to be considered when initiating a small stock improvement programme for trypanosomiasis-endemic areas.

The epidemiology of equine strongylosis in southern Queensland. 2. The survival and migration of infective larvae on herbage

The seasonal changes in longevity on herbage of the infective larvae of strongylid nematodes of the horse were studied. During the summer months, 1% of the larvae survived on herbage for 2-3 weeks, with 0.2% still viable for a further 2-3 weeks. Equivalent survival periods in winter were 7-11 weeks and over 11 weeks respectively. During spring and autumn, larvae survived for periods varying from 3-8 weeks. On Rhodes grass (Chloris gayana) growing vigorously in the summer of 1976, the majority of larvae remained in the lowest layers of the pasture, within 10 cm of the soil surface. Very few reached the highest fraction of grass sampled, above 40 cm from the soil. More larvae were recovered higher on the pasture in a period when less torrential rain had occurred. It was concluded that the parasitological benefits to be gained from short-term mixed grazing with horses and cattle may be minimal, in view of the tendency of cattle to eat only the upper layers of the pasture initially, with a consequent increase in the number of infective larvae per unit weight of herbage remaining.