The small-bat-in-summer paradigm: Energetics and adaptive behavioural routines of bats investigated through a stochastic dynamic model

Strong seasonality at high latitudes represents a major challenge for many endotherms as they must balance survival and reproduction in an environment that varies widely in food availability and temperature. To avoid energetic mismatches caused by limited foraging time and stochastic weather conditions, bats employ the energy-saving state of torpor during summer to save accumulated energy reserves. However, at high-latitude small-bats-in-summer face a particular challenge: as nocturnal foragers, they rely on the darkness at night to avoid predators and/or interspecific competition, but live in an environment with short, light summer nights, and even a lack of true night at the northernmost distributions of some bat species. To predict optimal behaviour in relation to latitudinal variation in diurnal cycles, we constructed a stochastic dynamic programming model of bats living at high latitudes. Using a stochastic dynamic programming framework with values that are representative for our study system, we show that individual energetic reserves are a strong driver of daytime use of torpor and night-time foraging behaviour alike, with these linked effects being both temperature- and photoperiod-dependent. We further used the model to predict survival probabilities at five locations across a latitudinal gradient (60.1° N to 70.9° N), finding that combinations of photoperiod and temperature conditions limited population distributions in the model. To verify our model results, we compared predictions for optimal decisions with our own empirical data collected on northern bats (Eptesicus nilssonii) from two latitudes in Norway. The similarities between our predictions and observations provide strong evidence that this model framework incorporates the most important drivers of diurnal decision-making in bat physiology and behaviour. Comparing empirical data and model predictions also revealed that bats facing lighter night conditions further north restrict their mass gain, which strengthens the hypothesis that predation threat is a main driver of bat nocturnality. Our model findings regarding state-dependent decisions in bats should contribute to the understanding of how bats cope with the summer challenges at high latitudes.

Co-evolution of cerebral and cerebellar expansion in cetaceans

Cetaceans possess brains that rank among the largest to have ever evolved, either in terms of absolute mass or relative to body size. Cetaceans have evolved these huge brains under relatively unique environmental conditions, making them a fascinating case study to investigate the constraints and selection pressures that shape how brains evolve. Indeed, cetaceans have some unusual neuroanatomical features, including a thin but highly folded cerebrum with low cortical neuron density, as well as many structural adaptations associated with acoustic communication. Previous reports also suggest that at least some cetaceans have an expanded cerebellum, a brain structure with wide‐ranging functions in adaptive filtering of sensory information, the control of motor actions, and cognition. Here, we report that, relative to the size of the rest of the brain, both the cerebrum and cerebellum are dramatically enlarged in cetaceans and show evidence of co‐evolution, a pattern of brain evolution that is convergent with primates. However, we also highlight several branches where cortico‐cerebellar co‐evolution may be partially decoupled, suggesting these structures can respond to independent selection pressures. Across cetaceans, we find no evidence of a simple linear relationship between either cerebrum and cerebellum size and the complexity of social ecology or acoustic communication, but do find evidence that their expansion may be associated with dietary breadth. In addition, our results suggest that major increases in both cerebrum and cerebellum size occurred early in cetacean evolution, prior to the origin of the major extant clades, and predate the evolution of echolocation.

Down-regulation of GPx1 mRNA and the loss of GPx1 activity causes cellular damage in the liver of selenium-deficient rabbits

The effects of 10 weeks of dietary selenium and/or vitamin E deficiency (< 0.03 mg Se and 1.5 mg vitamin E per kg diet) on body Se and vitamin E stores and on the down-regulation of liver cellular glutathione peroxidase (GPx1) and plasma glutathione peroxidase (GPx3) were examined in growing female New Zealand White rabbits in comparison to Se (+ 0.40 mg Se/kg diet) and/or vitamin E (+ 150 I.U./kg diet) supplemented controls. Additionally plasma lactate dehydrogenase (LDH) activity, liver thiobarbituric acid-reactive substances (TBA-RS) and liver protein carbonyls were measured to assess the development of oxidative stress during an alimentary Se and/or vitamin E deficiency. Significantly decreased concentrations of Se and vitamin E in plasma (Se: - 70%; vitamin E: - 87%) and liver (Se: - 90%; vitamin E: - 95%) indicated an efficacious Se and vitamin E depletion of the rabbits within 10 weeks. GPx1 messenger RNA levels (GPx1 mRNA) in the livers of Se-depleted rabbits were down-regulated to 1/3-1/8 of the Se supplemented controls. GPx1 enzyme activity in the livers of Se-deficient rabbits declined to 10% of the Se-supplied control rabbits. A significantly elevated LDH activity in the blood plasma of Se- and vitamin E-deficient rabbits indicated a general impairment of tissues. Markedly increased TBA-RS concentrations and protein carbonyl contents in the livers of Se- and vitamin E-deficient rabbits gave further evidence for severe oxidative damage of cellular lipids and proteins during an alimentary Se and/or vitamin E deficiency. Both a full expresssion of GPx1 attained by dietary Se supplementation and dietary vitamin E supply effected an almost complete protection against oxidative cellular damage of the liver.

A prospective sero-epidemiological study of visceral leishmaniasis in Baringo District, Rift Valley Province, Kenya

The incidence of visceral leishmaniasis (VL) was studied in 30 clusters with an average of 98 individuals in each cluster in a defined, endemic rural area of Baringo District, Kenya. The clusters were centred around recent cases of VL. Anti-leishmanial antibodies were measured by the direct agglutination test (DAT) and a clinical examination was performed on 2 occasions between April 1991 and May 1993. Of 2934 individuals tested by the DAT during the first visit, 78 (2.7%) were seropositive, 54 with and 24 without a history of VL. The seroconversion rate was 9/1000 person-years of observation (95% confidence interval 5.1-12.92) among 2332 seronegative individuals retested the following year. During the entire study period, VL was diagnosed in 10 patients, with an incidence rate of 2.2/1000 person-years of observation (95% confidence interval 0.8-3.6). Household contacts of individuals with previously confirmed VL had a higher frequency of DAT positivity than the rest of the population. This difference was significant for both sexes. These results suggest transmission in and around houses.

Visceral leishmaniasis: use of the polymerase chain reaction in an epidemiological study in Baringo District, Kenya

The polymerase chain reaction was applied to capillary blood spots dried on filter paper from 20 parasitologically proved cases of visceral leishmaniasis (VL), 21 subclinical cases, and 11 healthy controls in a longitudinal study of anthroponotic VL in Baringo District, Kenya. Leishmania deoxyribonucleic acid (DNA) was detected 10.5 months before diagnosis and up to 3 years after diagnosis and apparently successful treatment. Subclinical cases can have detectable circulating parasite DNA in their blood. These findings may indicate that subclinical cases can be a reservoir and formerly treated VL patients can remain a reservoir for a long time. Xenodiagnosis should be performed on subclinical cases and former VL patients to establish their role in transmission of VL in Kenya.

Studies on the prevalence of leishmanin skin test positivity in the Baringo District, Rift Valley, Kenya

The leishmanin skin test (LST) was applied in 26 clusters of an average of 97 individuals in Baringo District, Kenya. These clusters were centered around recent cases of visceral leishmaniasis (VL). Of 2,411 individuals tested, 254 (10.5%, 155 males and 99 females) had a positive reaction. Among cured VL patients, the frequency was approximately 30% and no sex difference was observed. In the population as a whole, LST positivity increased with age to a stable level from approximately 15 years of age, reflecting an endemic situation. The level of LST positivity was 25-30% and 10-15% in males and females, respectively. Uninfected household contacts of VL cases had a higher frequency of LST reactivity than the rest of the population. This relationship was significant only in females and children, the prevalence ratio being 2.3 (95% confidence interval 1.3-4.1), 1.9 (1.1-3.5), and 1.4 (0.8-2.5) for females, children, and males, respectively. The frequency of LST positivity was higher individuals living in wood houses than in individuals living in house with mud or stone walls. Again, this difference was significant only in females and children (P = 0.02 and P = 0.04), but not in males (P = 0.7). The results suggest that children and women are exposed to the parasite in or around their houses, whereas adult males are, in addition, exposed elsewhere.

Differential birthweights and the clinical relevance of birthweight standards in a multiethnic society

Using a computer-stored database, birthweights and related variables over 25,000 infants born in Amsterdam (The Netherlands) were analysed retrospectively. Only after allowing for maternal height, did the difference between mean birthweights of Dutch and Asian infants disappear, whereas Negroid and Mediterranean infants continued to show respectively lower and higher means than the others. These results confirm that the birthweight standards presently used are inappropriate for detection of deviant weight in non-Dutch groups.

Epidemiology and control of pertussis

An estimated 60 million children suffer from whooping cough annually, causing half a million deaths.

The gradual decline in incidence rates observed in Europe and North America even before the introduction of pertussis immunization is not likely to occur within the near future in developing countries short of widespread immunization efforts.

The present pertussis vaccine is effective, and serious adverse effects are rare in comparison with the consequences of the disease itself. A new, acel-lular vaccine is under trial and holds promise for the future.

Epidemiological studies and surveillance for pertussis activity are hampered by the fact that the clinical diagnosis is difficult to make under field conditions. New serological techniques may bring improvement in this respect.

Immunization does not play a significant role in outbreak control. Outbreak investigations are, however, extremely valuable for assessment of the effectiveness of immunization programmes; they provide valuable information, not easily obtained by other means, on age-specific attack rates and vaccine efficacy if the immunization status of the population is known.

Pertussis in a rural area of Kenya: epidemiology and results of a vaccine trial

Pertussis surveillance was carried out from 1974 to 1981 among a population of 24 000 in the Machakos district of Kenya by fortnightly or monthly home visits. The diagnosis was verified by a physician according to standard criteria including bacteriological and haematological findings. Since not all cases could be diagnosed with certainty, each case was scored from 0 to 3 according to the probability of pertussis. During the surveillance a vaccine trial was carried out: 436 children receiving two diphtheria-pertussis-tetanus (DPT) immunizations 6 months apart were compared with 466 children receiving the conventional three doses 3 months apart.The agglutinating antibody response was determined in approximately 100 children in the trial at 1 month, 2 years, 3(1/4) years and 4(1/4) years after completing the immunizations. The results showed no difference in titres between the 2-dose and 3-dose groups at one month after the last immunization. Waning of antibodies proceeded more rapidly in the 2-dose group, the differences between both groups becoming statistically significant after 2 years.Two epidemic waves of pertussis occurred during the seven years of surveillance. A third epidemic did not materialize, possibly because of increased herd immunity due to the immunizations. The case fatality rate was 1% and was highest (2.6%) among infants. During the 4 years following completion of the immunizations, 36 children in the vaccine trial, based on the cumulative probability of pertussis, yielded 16.7 cases. The number of "cases" so defined did not differ significantly between the two immunized groups, although there was a suggestion of greater protection with the 3-dose schedule. Compared with the observed number of "cases" among 1281 children of the same birth cohorts not included in the trial, the reduction among the trial children (both immunized groups) was 54%.

Agents affecting health of mother and child in a rural area of Kenya. XVII. Population growth in 1974-1978

Demographic information was collected on a fortnightly basis between 1974 and 1978 in the framework of the Machakos Project. Results reported here deal with population size and increase on a de jure and de facto basis, population composition by age and sex, and crude birth and death rates. The results show that the study area is characterized by somewhat lower fertility than the national average of Kenya and much lower mortality. In addition, there is net-in-migration into the study area and the overall result is very rapid population increase. It is argued that underreporting of births and deaths, has been kept to a minimum due to the design that was used together with the use of several control measures.

Agents affecting health of mother and child in a rural area of Kenya. XVIII. Fertility, mortality and migration in 1975-1978

The results reported here are based on age-specific rates and are, therefore, more sensitive and meaningful as indicators of fertility and mortality than the crude rates mentioned in the previous article. The results confirm that, compared to world standards, the study area is characterized by a high level of fertility and a fairly low level of mortality. Fertility and mortality are, however, lower in the study area in comparison to Kenya as a whole. Another characteristic is high population mobility which is of two types: temporary migration of absent members of the population, and permanent in- and out-migration.

Machakos Project Studies: agents affecting health of mother and child in a rural area of Kenya. XVI. The outcome of pregnancy

The outcome of pregnancy of all women belonging to the study population of the Machakos project studies who delivered during 1975 and 1976 is presented. The birth-rate was 43.0 per 1,000 population per year, the fertility rate was 235 per 1,000 women 15--44 years of age per year. Unexpected low mortality rates were found; stillbirths, neonatal and infant death rates were respectively 29.8 per 1,000 total births and 22.5 and 50.0 per 1,000 live births. One maternal death occurred among the 2,223 deliveries. Maternal age of less than 25 and over 34 years, a history of previous perinatal death and breech delivery were associated with higher perinatal mortality. Parity, marital status, birth-interval and maternal height were not associated with a difference in outcome of pregnancy. The stillbirth rate among the children born in hospital (26.4%) was 4.4% compared with 2.4% among the children born at home, neonatal and infant death rates were the same. Half of all perinatal deaths were caused by either prematurity or birth trauma, 75% of all infant deaths after the first week of life were caused by infections.

Agents affecting health of mother and child in a rural area of Kenya. XI. Antibodies against rotavirus in sera from children living in the Machakos District of Kenya

207 sera from children under 5 years of age and living in the Machakos District in Kenya were tested in the Complement Fixation Test for antibodies against rotavirus. Two different antigens were used. The superiority of 'O' antigen over Nebraska calf diarrhoea virus antigen was confirmed. After a fall to 29 percent in the 6-8 months age group, the percentage of children with antibodies quickly rises with age to 80 percent at the age of 24 months and to practically 100 percent at the age of 30 months. This age-immunity curve suggests that the majority of children contract infections with rotavirus between 6 and 23 months of age. This is conform the pattern usually found in temperate climate countries.

Machakos Project Studies: agents affecting health of mother and child in a rural area of Kenya. VII. The incidence of diarrhoeal disease in the under-five population

The outcome of three years of fortnightly diarrhoea surveillance of about 4000 children under the age of five is described. The two-weekly incidence of diarrhoea in children in the age group 0-5 months, 6-11 months and 12-23 months, who were reported and/or observed to be ill, was 3.4%, 5.6% and 3.4% respectively. A decline in the attack rates of diarrhoea not associated with measles at the end of 1975 and the beginning of 1976 corresponds with a similar decline in the incidence of measles and malnutrition. Initially diarrhoea information was only obtained from children who where reported and/or observed to be ill; later on, all mothers were questioned about their children's diarrhoea experience at the moment of the fieldworkers's visit or in the preceding two weeks. This yielded a four to sevenfold increase in diarrhoea incidence. Thus, diarrhoea appears to be a common condition among under-fives which is not necessarily considered to be an illness by the mother.

Agents affecting health of mother and child in a rural area of Kenya. III. The epidemiology of measles

Between April 1974 and March 1976 surveillance of measles has been conducted by 12 fieldworkers making fortnightly home visits among a total population of 24,000 living in nearly 4000 households scattered in variable density throughout an area of 87 sq km in the northern division of the Machakos district, Kenya. The diagnosis of measles was verified by one of the project's physicians according to standardized procedures and was, whenever possible, supported by virus isolation and serum antibody level determination. Because not all reported patients were actually seen during the period of clinical manifestations, the diagnosis remained doubtful in a number of cases. Incidence and mortality figures have been estimated with 95% confidence limits based on the assumption that doubtful cases represent a probability of measles of .33 and probable cases a probability of .67. The estimated attack rate for the susceptible population 0-15 years of age was 13.5%. When related to all children--susceptible or not--the attack rate was highest in the 1-2 years age group (11%). Almost 15% of cases occurred below the age of one year, 1% below 6 months of age and 6% between 6 and 8 months. The estimated case fatality rate was 6.5%, fatality being highest between 1 and 2 years of age. For the age group 0-15 years measles accounted for 16.7% of all deaths. The estimated death rate per 100,000 total population was 113. The epidemiological pattern of measles suggests continuous re-introduction of the measles virus in a dispersed population causing micro-outbreaks of the disease in geographically widely separated spots throughout the year which tends to keep the proportion of susceptibles down and the attack rate during a protracted epidemic relatively low.

Machakos project studies. Agents affecting health of mother and child in a rural area of Kenya. II. The diagnosis of measles under field conditions

The measles signs of children reported for measles were recorded on a check list of clinical signs. The presence and absence of these signs for a measles group (M) and a control group (C) were subject of a statistical analysis. The M and C group were determined by the results of laboratory determinations. A prediction score was derived by means of minimal paths analysis, used in reliability networks. The clinical score, based on certain criteria, the prediction score and the result of laboratory determinations were combined in order to reach a final diagnosis. A comparison of the clinical diagnosis and the final diagnosis showed a considerable overlap of the two diagnoses. The conclusion was that the clinical diagnosis only is sufficient to reach adequate incidence rates in the case of a measles epidemic.

Poliomyelitis: epidemiology and prophylaxis. 5. Results of a two- and three-dose vaccination experiment

In tropical countries, seroconversion rates following oral poliomyelitis vaccination are frequently unsatisfactory. In an area of the Machakos district in Kenya, 4000 children under 5 years of age have been registered and are visited fortnightly by trained field staff as part of a comprehensive, population-based, longitudinal surveillance project. It was considered possible that poliomyelitis vaccine, given orally to children twice or three times at home, would produce satisfactory conversion rates. After collection of blood from a random sample of the children, vaccine was given twice to all children under 5 years of age. Blood was then collected a second time from a different sample of children. After a third dose of vaccine, a third blood collection followed. The percentages of the children that received vaccine each round were calculated and the sera tested for antibodies. It appeared that the mean titre was more strongly related to age than to the number of doses of poliomyelitis vaccine received. Improvement of herd immunity after two vaccine distributions was significant for a few age groups and for two types of vaccine only. In none of the groups was a significant improvement obtained by the third vaccine distribution. The problems associated with vaccination by live poliomyelitis vaccine in tropical countries are discussed in relation to the results.

Rheumatoid factor in Nigerian sera

A high prevalence of rheumatoid factor has been found in the sera of apparently healthy inhabitants of two Western Nigerian villages. The prevalence of rheumatoid factor at high titre increased markedly with age. The rheumatoid factor found in the sera of these apparently healthy subjects showed a selective affinity for human γ-globulin rather than rabbit γ-globulin. Rheumatoid factor activity was shown to be restricted to the serum IgM fraction. In one of the two villages a significant correlation was found between the presence of rheumatoid factor at high titre and the presence of IgM malaria antibodies at high titre and the possible role of malaria in the induction of rheumatoid factor formation in these two communities is discussed.