Meningoencephalitis Due to Listeria monocytogenes in a Pregnant Rhesus Macaque (Macaca mulatta)

We here report a spontaneous case of meningoencephalitis due to Listeria monocytogenes in an adult primiparous rhesus macaque (Macaca mulatta) during an outbreak of listeriosis in an outdoor enclosure. Clinical signs included tremors, abnormal posture, and altered mental status. Hematology and analyses of cerebrospinal fluid were consistent with bacterial infection. Pure cultures of L. monocytogenes were recovered from the placenta–abortus, cerebrospinal fluid, and brain tissue. The macaque did not respond to treatment and was euthanized. Histopathologic examination of the brain revealed acute meningoencephalitis. This case represents an unusual clinical and pathologic presentation of listeriosis in a nonhuman primate in which the dam and fetus both were affected.Listeria monocytogenes is a ubiquitous, facultative anaerobic, intracellular gram-positive coccobacillus. This bacterium is found in diverse environments including (but not limited to) soil, water, plant matter, food items, and the intestinal tract of mammalian hosts.^15,18 The organism is environmentally resistant, being able to survive in dried media for several months and in moist soil for up to a year.¹⁵ L. monocytogenes is the causative agent of listeriosis, a bacterial infection that has a worldwide distribution and affects a wide range of mammals and birds, including human beings.In people, L. monocytogenes is a relatively uncommon foodborne pathogen; its abilities to survive food processing and grow in cold conditions allow it to persist in appropriately stored or refrigerated foods.² In people, listeriosis occurs both sporadically and as large outbreaks,¹⁸ generally comprising 3 separate syndromes with clinical manifestations ranging from mild to life-threatening.³⁵ The most common form is seen in immunocompetent, nonpregnant adults as a febrile gastroenteritis.^2,18,21 The other 2 forms, which occur in fetuses and immunocompromised patients, are more severe.^19,21 In pregnant women, maternal listeriosis is asymptomatic or causes mild, flu-like symptoms, but the bacterium''s ability to cross the placenta and the blood–brain barrier of the fetus results in neonatal septicemia, meningitis, abortion, and stillbirth.¹⁶ In elderly and immunocompromised patients, septicemia and meningoencephalitis are life-threatening manifestations of literiosis.²⁶ The worldwide case fatality rate varies widely among countries, sometimes exceeding 50% despite what is considered to be appropriate antibiotic therapy.¹⁸ In 2009, the Centers for Disease Control reported 524 cases of listeriosis in the United States, which were associated with a 19% resulting in death.⁴In ruminants, listeriosis is also known as ‘circling disease’ and ‘silage disease.’^8,18,21 Foodborne infection with L. monocytogenes is well described, and many studies have shown that spoiled silage may be a source of listeria outbreaks.^8,18 Rhombencephalitis and diffuse meningoencephalitis are the most recognized forms of the infection in ruminants; sporadic abortion is reported also.²² Clinical signs of listeria encephalitis in cattle, sheep, and goats are characterized by unilateral or bilateral brainstem dysfunction and cranial nerve deficits. In sheep and goats, the course of the disease is acute, but the disease in cattle has a more chronic progression, with neurologic manifestations that can last 4 to 14 d.^1,22In rabbits, infection with L. monocytogenes is characterized by abortion in pregnant does or sudden death; neurologic signs are rare.¹ In poultry, an acute form with septicemia and sudden death occurs in adults, in contrast to a subacute–chronic form, with encephalitis, in the young.⁶The literature on L. monocytogenes in nonhuman primates is sparse^5,11,17,33 and more recently limited to experimental infection of pregnant animals. In pregnant rhesus macaques (Macaca mulatta), experimental infection during the last trimester of gestation can cause stillbirth with no other clinical signs.^23,24 In our colony, however, infection with L. monocytogenes is endemic. Every year, several spontaneous abortions or stillbirths in our outdoor colony are caused by infection of the dam with this organism. Culture of L. monocytogenes from both the abortus–fetus and placenta are well documented. As described in the literature,^23,24 the dams in our colony do not demonstrate any clinical signs prior to the abortion or stillbirth.During the winter to spring of 2011, one of our outdoor housing enclosures experienced an outbreak of listeriosis. This outside corral housed 100 rhesus macaques in a social group that included 42 reproductive females. Of these reproductive females, 37 (88%) were confirmed pregnant by abdominal palpation or ultrasonography or both. From January 2011 to May 2011, 19 (51%) stillbirths and neonatal deaths (in infants younger than 3 d) were reported in this enclosure; 13 (68%) of these tissues (placenta, 3; fetal lungs, 8; fetal peritoneum, 2) were culture-positive for L. monocytogenes. In all cases except the one presented here, the dam did not manifest any clinical signs prior to or after the delivery of a stillborn or premature birth with neonatal death.Here we describe an unusual case of listeriosis in a primiparous pregnant female rhesus macaque that manifested severe neurologic impairment and intrautero death of the fetus.     

Modeling the dynamics of woody plant–herbivore interactions with age-dependent toxicity

In this paper we study the effects that woody plant chemical defenses may have on interactions between boreal hares that in winter feed almost entirely on twigs. We focus particularly on the fact that toxin concentration often varies with the age of twig segments. The model incorporates the fact that the woody internodes of the youngest segments of the twigs of the deciduous angiosperm species that these hares prefer to eat are more defended by toxins than the woody internodes of the older segments that subtend and support the younger segments. Thus, the per capita daily intake of the biomass of the older segments of twigs by hares is much higher than their intake of the biomass of the younger segments of twigs. This age-dependent toxicity of twig segments is modeled using age-structured model equations which are reduced to a system of delay differential equations involving multiple delays in the woody plant-hare dynamics. A novel aspect of the modeling was that it had to account for mortality of non-consumed younger twig segment biomass when older twig biomass was bitten off and consumed. Basic mathematical properties of the model are established together with upper and lower bounds on the solutions. Necessary and sufficient conditions are found for the linear stability of the equilibrium in which the hare is extinct, and sufficient conditions are found for the global stability of this equilibrium. Numerical simulations confirmed the analytical results and demonstrated the existence of limit cycles over ranges of parameters reasonable for hares browsing on woody vegetation in boreal ecosystems. This showed that age dependence in plant chemical defenses has the capacity to cause hare-plant population cycles, a new result.     

Plant allocation of carbon to defense as a function of herbivory,light and nutrient availability

We use modeling to determine the optimal relative plant carbon allocations between foliage, fine roots, anti-herbivore defense, and reproduction to maximize reproductive output. The model treats these plant components and the herbivore compartment as variables. Herbivory is assumed to be purely folivory. Key external factors include nutrient availability, degree of shading, and intensity of herbivory. Three alternative functional responses are used for herbivory, two of which are variations on donor-dependent herbivore (models 1a and 1b) and one of which is a Lotka–Volterra type of interaction (model 2). All three were modified to include the negative effect of chemical defenses on the herbivore. Analysis showed that, for all three models, two stable equilibria could occur, which differs from most common functional responses when no plant defense component is included. Optimal strategies of carbon allocation were defined as the maximum biomass of reproductive propagules produced per unit time, and found to vary with changes in external factors. Increased intensity of herbivory always led to an increase in the fractional allocation of carbon to defense. Decreases in available limiting nutrient generally led to increasing importance of defense. Decreases in available light had little effect on defense but led to increased allocation to foliage. Decreases in limiting nutrient and available light led to decreases in allocation to reproduction in models 1a and 1b but not model 2. Increases in allocation to plant defense were usually accompanied by shifts in carbon allocation away from fine roots, possibly because higher plant defense reduced the loss of nutrients to herbivory.     

Basic Fuchsin for Staining Vascular Bundles

The following procedure has been found helpful in tracing the vascular supply of succulent plants, such as the garden pea, Pisum sativum. It has been used as a supplementary means of study only, to microscopic slides cut serially thru the plant.     

Embryonic and fetal development in a commercial dam-line genotype

During depopulation of a breeding unit within Swine Graphics Enterprises, extensive data were collected and used to examine relationships among ovulation rate, the pattern of prenatal loss, and placental and fetal development. Groups of Large White x Landrace females (n=447) were slaughtered between day 20-30, 50-55 or 85-90 of gestation, with approximately equal numbers of animals representing gilts and parity 1 (G/P1), parity 2-3 (P2/3), and parity >4 (P4+). Ovulation rate and embryo number were recorded for all animals. With the exception of the G/P1 animals, embryonic and placental weight were recorded for four conceptuses per sow on day 20-30; on day 85-90 two conceptuses per sow were dissected to determine placental and fetal development. Ovulation rate (22.7 +/- 0.2 overall) was higher (P <0.05) in P2/3 (23.6 +/- 0.4) and P4+ (24.7 +/- 0.4) than in G/P1 (20.2 +/- 0.5). Embryonic/fetal survival was 61.8 +/- 2.1% at day 20-30, 50.2 +/- 2.2% at day 50-55 and 48.7 +/- 1.9% at day 85-90 and the number of surviving conceptuses was higher (P <0.05) in the P2/3 sows than in other parity groups. There was no relationship between ovulation rate and number of live embryos at day 20-30 or 85-90. At day 20-30 and 85-90, embryo weight was positively correlated with placental weight, but neither placental weight nor embryonic/fetal weight was correlated with number of viable embryos. A parity by gestation day interaction existed; placental weight for P4+ (3.42 +/- 0.43 g) was less than for P2/3 (7.55 +/- 0.40 g) at day 20-30 (P <0.0001), whereas at day 85-90, placental weight of P2/3 (209.5 +/- 8.5 g) was less (P=0.05) than both G/P1 (235.7 +/- 7.3g) and P4+ (235.4 +/- 7.1 g). At day 85-90, fetal brain weight, relative to body weight (R2=0.61, P <0.0001), and fetal brain:liver weight ratio (R2=0.35; P <0.0001) were negatively related to mean fetal weight, and brain:liver weight ratio showed a trend towards a relationship with number of viable fetuses (P=0.08). Parity also affected brain:liver weight ratio (P=0.01). Clearly, high ovulation rates in the higher parity sows have the potential to cause excessive in utero crowding of conceptuses in the post-implantation period. Even with moderate crowding, increased brain:liver weight ratios in smaller fetuses in late gestation indicate that uterine capacity impacts fetal development as well as the number of surviving fetuses.     

Functional variation among frugivorous birds: implications for rainforest seed dispersal in a fragmented subtropical landscape

Seed dispersal plays a critical role in rainforest regeneration patterns, hence loss of avian seed dispersers in fragmented landscapes may disrupt forest regeneration dynamics. To predict whether or not a plant will be dispersed in fragmented forests, it is necessary to have information about frugivorous bird distribution and dietary composition. However, specific dietary information for frugivorous birds is often limited. In such cases, information on the seed-crushing behaviour, gape width and relative dietary dominance by fruit may be used to describe functional groups of bird species with respect to their potential to disperse similar seeds. We used this information to assess differences in the seed dispersal potential of frugivorous bird assemblages in a fragmented rainforest landscape of southeast Queensland, Australia. The relative abundance of frugivorous birds was surveyed in extensive, remnant and regrowth rainforest sites (16 replicates of each). Large-gaped birds with mixed diets and medium-gaped birds with fruit-dominated diets were usually less abundant in remnants and regrowth than in continuous forest. Small-gaped birds with mixed diets and birds with fruit as a minor dietary component were most abundant in regrowth. We recorded a similar number of seed-crushing birds and large-gaped birds with fruit-dominated diets across site types. Bird species that may have the greatest potential to disperse a large volume and wide variety of plants, including large-seeded plants, tended to be less abundant outside of extensive forests, although one species, the figbird Sphecotheres viridis, was much more abundant in these areas. The results suggest that the dispersal of certain plant taxa would be limited in this fragmented landscape, although the potential for the dispersal of large-seeded plants may remain, despite the loss of several large-gaped disperser species.     

A predator-prey reaction-diffusion system with nonlocal effects

We consider a predator-prey system in the form of a coupled system of reaction-diffusion equations with an integral term representing a weighted average of the values of the prey density function, both in past time and space. In a limiting case the system reduces to the Lotka Volterra diffusion system with logistic growth of the prey. We investigate the linear stability of the coexistence steady state and bifurcations occurring from it, and expressions for some of the bifurcating solutions are constructed. None of these bifurcations can occur in the degenerate case when the nonlocal term is in fact local.