Dynamics of a novel pathogen in an avian host: Mycoplasmal conjunctivitis in house finches

In early 1994, a novel strain of Mycoplasma gallisepticum (MG)--a poultry pathogen with a world-wide distribution--emerged in wild house finches and within 3 years had reached epidemic proportions across their eastern North American range. The ensuing epizootic resulted in a rapid decline of the host population coupled with considerable seasonal fluctuations in prevalence. To understand the dynamics of this disease system, a multi-disciplinary team composed of biologists, veterinarians, microbiologists and mathematical modelers set forth to determine factors driving and influenced by this host-pathogen system. On a broad geographic scale, volunteer observers ("citizen scientists") collected and reported data used for calculating both host abundance and disease prevalence. The scale at which this monitoring initiative was conducted is unprecedented and it has been an invaluable source of data for researchers at the Cornell Laboratory of Ornithology to track the spread and magnitude of disease both spatially and temporally. At a finer scale, localized and intensive field studies provided data used to quantify the effects of disease on host demographic parameters via capture-mark-recapture modeling, effects of host behavior on disease and vice-versa, and the biological and genetic profiles of birds with known phenotypic characteristics. To balance the field-based component of the study, experiments were conducted with finches held in captivity to describe and quantify the effects of experimental infections on hosts in both individual and social settings. The confluence of these various elements of the investigation provided the foundation for construction of a general compartmentalized epidemiological model of the dynamics of the house finch-MG system. This paper serves several purposes including (i) a basic review of the pathogen, host, and epidemic cycle; (ii) an explanation of our research strategy; (iii) a basic review of results from the diverse multi-disciplinary approaches employed; and (iv) pertinent questions relevant to this and other wildlife disease studies that require further investigation.     

Vector competence of eastern and western forms of Psorophora columbiae (Diptera: Culicidae) mosquitoes for enzootic and epizootic Venezuelan equine encephalitis virus

Venezuelan equine encephalitis virus (VEEV) continues to circulate enzootically in Mexico with the potential to re-emerge and cause disease in equines and humans in North America. We infected two geographically distinct mosquito populations of eastern Psorophora columbiae form columbiae (Chiapas, Mexico and Texas, United States) and one mosquito population of western Psorophora columbiae form toltecum (California, United States) with epizootic and enzootic IE VEEV and epizootic IAB VEEV. We detected no differences between epizootic and enzootic IE viruses in their ability to infect any of the mosquito populations analyzed, which suggested that neither species selects for epizootic IE viruses. Psorophora columbiae f. columbiae (Texas) were significantly less susceptible to infection by epizootic IE than Ps. columbiae f. columbiae (Mexico). Psorophora columbiae f. toltecum populations were more susceptible than Ps. columbiae f. columbiae populations to epizootic IE and IAB viruses.     

Seroepidemiological Survey of West Nile Virus Infections in Horses from Berlin/Brandenburg and North Rhine-Westphalia,Germany

Following the introduction of the West Nile virus (WNV) into eastern Germany in 2018, increasing infections have been diagnosed in birds, equines, and humans over time, while the spread of WNV into western Germany remained unclear. We screened 437 equine sera from 2018 to 2020, excluding vaccinated horses, collected from convenience sampled patients in the eastern and western parts of Germany, for WNV-specific antibodies (ELISAs followed by virus/specific neutralization tests) and genomes (RT-qPCRs). Clinical presentations, final diagnoses, and demographic data were also recorded. In the eastern part, a total of eight horses were found WNV seropositive in 2019 (seroprevalence of 8.16%) and 27 in 2020 (13.77%). There were also two clinically unsuspected horses with WNV-specific antibodies in the western part from 2020 (2.63%), albeit travel history-related infections could not be excluded. None of the horse sera contained WNV-specific genomes. Eight horses in eastern Germany carried WNV-IgM antibodies, but only four of these showed typical clinical signs. These results underline the difficulty of detecting a WNV infection in a horse solely based on clinical signs. Thus, WNV circulation is established in the horse population in eastern Germany, but not yet in the western part.     

Vicariance biogeography in the Pleistocene and speciation in North American wood warblers: a test of Mengel's model

It is widely believed that habitat fragmentation during the Pleistocene initiated speciation events in many songbird genera. One such vicariance model for avian speciation in the Pleistocene was developed by R. M. Mengel for North American birds. This model suggests that the first Pleistocene glacial advance reduced the area of an extensive, eastern North American deciduous forest, forcing adaptation by some species to boreal forest. This, in turn, facilitated the development of transcontinental range expansions during interglacials. Subsequent glacial advances repeatedly fragmented the ranges of these species into eastern and western populations; western isolates speciated to form the multispecies groups observed among various North American birds. We used mtDNA restriction site data to reconstruct the phylogeny of the black-throated green warbler complex-the group that Mengel considered the best fit to his model. Contrary to Mengel's model, the phylogeny indicates that not all western endemics were derived from an eastern ancestor. Instead, our results imply a mix, wherein some western endemics were budded off an eastern source, as Mengel posits, while others probably resulted from intermontane isolations in the west.     

Mycoplasma gallisepticum infection in house finches (Carpodacus mexicanus) affects mosquito blood feeding patterns

Disease-induced lethargy can diminish host capacity to repel or kill biting mosquitoes. We exposed house finches (Carpodacus mexicanus) to mosquitoes (Culex pipiens pipiens), repeated the experiment after inoculating finches with Mycoplasma gallisepticum, and then repeated the experiment with the same birds after curing their infections. We videotaped avian behaviors before and during mosquito exposure, identifying hosts through blood meal DNA fingerprinting. Results revealed heterogeneity in mosquito preference regardless of infection. Mosquitoes choosing between two healthy finches were more likely to feed upon the same individual bird consistently. When one bird was sick, mosquitoes exhibited no preference. Sick birds made fewer total defensive behaviors than healthy birds, but only foot stomps were associated with reduced mosquito feeding success. Our results suggest that Mycoplasma and other avian infections that alter bird defensive behavior may influence mosquito feeding patterns and transmission of arthropod-borne pathogens such as West Nile virus.     

Ontogenetic modification of the hypercapnic ventilatory response in the zebra finch.

We investigated the effect of exposure to CO2 during development on the adult ventilatory response to CO2 of zebra finches. Developing zebra finches were exposed to chronic hypercapnic respiratory environments as embryos, as nestlings or during both developmental periods. Their responsiveness to CO2 was then measured following a 125-135 day post-fledging deacclimation period. At a FICO2 of 0.06, mean ventilation of adult finches in the three groups was 74.8, 61.3 and 65.8%, respectively, of that of finches reared under normocapnic conditions. These data indicate that adult acute ventilatory responsiveness to CO2 in birds may be in part determined by CO2 exposure during early development and may help explain the observation that fossorial and semifossorial species of birds and mammals, that naturally encounter high CO2 conditions in their burrows, have a blunted hypercapnic ventilatory response.     

Investigations of the vertebrate hosts of eastern equine encephalitis during an epizootic in Michigan, 1980

A study was undertaken to investigate an increase in reported cases of clinical encephalitis due to eastern equine encephalitis (EEE) virus in horses and to determine the natural vertebrate hosts of that virus. Horses, birds, and small mammals were sampled at sites in a contiguous area in St. Joseph and Kalamazoo counties, Michigan, from 25 August to 5 September 1980. Serum samples from four horses acutely ill with encephalitis and 16 of 39 pasture mates of ill horses had neutralizing (N) antibody against EEE virus (46.5%); no viruses were isolated from these 43 sera. None of 24 draft horses from a site in St. Joseph County 12 km southeast of the affected sites had EEE antibody. A strain of Cache Valley virus was isolated from the blood of one of the 24 draft horses. No viruses were isolated, and no antibodies to EEE virus were detected in 28 blood samples from small mammals captured at sites where equine cases of encephalitis were occurring. Six strains of EEE virus, five of Highlands J virus, and one of Flanders virus were isolated from the blood of 401 wild birds belonging to 42 species captured at eight sites in both counties. A total of 29.9% of the wild birds had EEE antibody. Five species of domestic birds, mostly chickens and ring-necked pheasants, were sampled in both counties. Six strains of EEE virus were isolated from 152 ring-necked pheasants; these included three isolates from the brains of dead birds. About 13% of 51 pheasants tested from two small flocks in backyard pens in Kalamazoo County and 9% of 103 pheasants tested from a large game farm in St. Joseph County had antibody to EEE virus. The source of the EEE virus and the factors responsible for this epizootic are unknown; however, the epizootic probably represented an explosive expansion of an enzootic level of virus transmission.     

Prolactin release and response to vasoactive intestinal peptide in an opportunistic breeder, the zebra finch (Taeniopygia guttata)

Zebra finches in arid regions of Australia are opportunistic breeders that time their breeding cycles to coincide with nonseasonal rainfall. Hormonal profiles associated with reproductive behaviors may differ from those observed in seasonal breeders because these birds need to be reproductively competent on short notice. This study measured plasma prolactin (PRL) levels in nonbreeding and breeding zebra finches and in birds with and without prior reproductive experience. We also investigated the change in plasma PRL following injection with vasoactive intestinal peptide (VIP), the avian PRL-releasing hormone. PRL was lowest in non-paired birds, increased after pair bonds had formed, and was highest in incubating birds. No differences in PRL levels were found between males and females in these biparental care-givers. A single injection of VIP resulted in a rapid increase in plasma PRL in nonbreeding zebra finches, while PRL remained unchanged in incubating birds. When escalating doses of VIP were administered, nonbreeders responded with a maximal response in PRL release, but PRL levels in breeders remained unchanged following even the highest VIP dose. Among nonbreeders, inexperienced birds had significantly lower PRL levels than birds that had successfully reared a clutch, but both groups responded with an equally robust increase in PRL following a VIP challenge. This pattern differs from that observed in most photosensitive species in which only during a breeding cycle do birds secrete significant levels of PRL in response to exogenous VIP. Zebra finches, even when not actively breeding, must maintain competent pituitary lactotrophs that can secrete PRL at maximal rates. This is part of the suite of characters enabling these birds to respond to favorable breeding conditions at any time.     

Simulation studies of St. Louis encephalitis and West Nile viruses: the impact of bird mortality

West Nile virus (WNv) has spread through much of the eastern United States following its introduction in 1999, and arrived in Florida in 2001. Prior to its arrival, we anticipated that its transmission cycle was likely to be similar to that of St. Louis encephalitis virus (SLEv). However, high levels of avian mortality have been reported for WNv in the northeastern United States, and it was unknown how this would impact the transmission dynamics of WNv. Simulation models were used to compare the two viruses by considering the impact of bird mortality on the transmission dynamics of arboviruses in south Florida. Transmission models without disease-induced mortality (SLEv) were compared with models including disease-induced mortality (WNv). Disease-induced mortality depressed transmission, eliminating epizootics in two of 14 simulations that were epizootic without the additional mortality. In both models, the most important factor in the likelihood of epizootics was mosquito population size; the mosquito mortality rate was also important. The additional avian mortality altered the factors most important in the size and timing of epizootics, although it did not always directly affect the outcome of the simulations. In some cases, low-level transmission occurred prior to the epizootic peak. When disease-induced avian mortality was included in the simulations, appreciable numbers of dead birds occurred prior to high levels of infection in mosquitoes. This has implications for the use of dead birds as a surveillance tool monitoring the spread and transmission of WNv.     

Eastern equine encephalomyelitis in upstate New York: studies of a 1976 epizootic by a modified serologic technique, hemagglutination reduction, for rapid detection of virus infections.

An extensive outbreak of eastern equine encephalomyelitis (EEE) occurred in upstate New York during the summer of 1976, with 37 cases confirmed in horses by isolation of virus and/or by serologic examination. Other specimens collected in the affected area yielded 16 further isolates: 9 from 818 pools of 33,365 mosquitoes, 5 from tissues of 64 birds and 2 from 4 sentinel pheasants with serologic conversions. EEE antibodies were also detected in 81 of 499 wild birds tested. Our data implicate sparrows, cowbirds, and catbirds in the amplification of EEE virus and Culiseta melanura mosquitoes as vectors among avians. During the course of this epizootic a modified serologic technique involving hemagglutination reduction gave reliable diagnoses of EEE as early as 24 hours after receipt of field specimens.     

Reconstructing the origin and spread of horse domestication in the Eurasian steppe

Despite decades of research across multiple disciplines, the early history of horse domestication remains poorly understood. On the basis of current evidence from archaeology, mitochondrial DNA, and Y-chromosomal sequencing, a number of different domestication scenarios have been proposed, ranging from the spread of domestic horses out of a restricted primary area of domestication to the domestication of numerous distinct wild horse populations. In this paper, we reconstruct both the population genetic structure of the extinct wild progenitor of domestic horses, Equus ferus, and the origin and spread of horse domestication in the Eurasian steppes by fitting a spatially explicit stepping-stone model to genotype data from >300 horses sampled across northern Eurasia. We find strong evidence for an expansion of E. ferus out of eastern Eurasia about 160 kya, likely reflecting the colonization of Eurasia by this species. Our best-fitting scenario further suggests that horse domestication originated in the western part of the Eurasian steppe and that domestic herds were repeatedly restocked with local wild horses as they spread out of this area. By showing that horse domestication was initiated in the western Eurasian steppe and that the spread of domestic herds across Eurasia involved extensive introgression from the wild, the scenario of horse domestication proposed here unites evidence from archaeology, mitochondrial DNA, and Y-chromosomal DNA.     

A novel highly pathogenic H5N8 avian influenza virus isolated from a wild duck in China

Migrating wild birds are considered natural reservoirs of influenza viruses and serve as a potential source of novel influenza strains in humans and livestock. During routine avian influenza surveillance conducted in eastern China, a novel H5N8 (SH‐9) reassortant influenza virus was isolated from a mallard duck in China. blast analysis revealed that the HA, NA, PB1, PA, NP, and M segments of SH‐9 were most closely related to the corresponding segments of A/duck/Jiangsu/k1203/2010 (H5N8). The SH‐9 virus preferentially recognized avian‐like influenza virus receptors and was highly pathogenic in mice. Our results suggest that wild birds could acquire the H5N8 virus from breeding ducks and spread the virus via migratory bird flyways.     

Spatiotemporal analysis of epizootic raccoon rabies propagation in Connecticut, 1991-1995

The quantitative analysis of pathogen transmission within its specific spatial context should improve our ability to predict and control the epizootic spread of that disease. We compared two methods for calibrating the effect of local, spatially distributed environmental heterogeneities on disease spread. Using the time-of-first-appearance of raccoon rabies across the 169 townships in Connecticut, we estimated local spatial variation in township-to-township transmission rate using Trend Surface Analysis (TSA) and then compared these estimates with those based on an earlier probabilistic simulation using the same data. Both the probabilistic simulation and the TSA reveal significant reduction in transmission when local spatial domains are separated by rivers. The probabilistic simulation suggested that township-to-township transmission was reduced sevenfold for townships separated by a river. The global effect of this sevenfold reduction is to increase the time-to-first-appearance in the eastern townships of Connecticut by approximately 29.7% (spread was from west to east). TSA revealed a similar effect of rivers with an overall reduction in rate of local propagation due to rivers of approximately 22%. The 7.7% difference in these two estimates reveals slightly different aspects of the spatial dynamics of this epizootic. Together, these two methods can be used to construct an overall picture of the combined effects of local spatial variation in township-to-township transmission on patterns of local rate of propagation at scales larger than the immediate nearest neighboring townships.     

Batai Orthobunyavirus: An Emerging Mosquito-Borne Virus in Europe

Batai virus (BATV) is a zoonotic orthobunyavirus transmitted by a wide range of mosquito vectors. The virus is distributed throughout Asia and parts of Africa and has been sporadically detected in several European countries. There is increasing evidence that BATV is emerging in Europe as a potential threat to both animal and human health, having been detected in mosquitoes, mammals, birds and humans. In recent years, serological surveillance in cattle, sheep and goats has suggested an antibody prevalence of up to 46% in European livestock, although human serological prevalence remains generally low. However, the recent and continued spread of invasive mosquito species into Europe may facilitate the establishment of competent populations of mosquitoes leading to increased BATV transmission. Migratory birds may also potentially facilitate the emergence of BATV in geographical locations where it was previously undetected. Although BATV has the potential to cause disease in humans and livestock, our understanding of the impact in wild animal populations is extremely limited. Therefore, there is a need for increased surveillance for BATV in mosquitoes, livestock, wild mammals and birds in Europe to understand the true impact of this virus.     

Molecular epidemiology of Plasmodium falciparum resistance to antimalarial drugs in Indonesia

The extent of gene polymorphisms associated with resistance to chloroquine and sulfadoxine-pyrimethamine was examined in field isolates of Plasmodium falciparum from Indonesia. Eight malaria-endemic areas, representing a broad region of the western and eastern Indonesian Archipelago were surveyed. Blood from 20-50 patients was collected at each site, DNA was isolated, and the sequences of four different genes (dihydrofolate reductase [dhfr], dihydropteroate synthase [dhps], P. falciparum multidrug resistance 1 [pfmdr1], and P. falciparum chloroquine resistance transporter [pfcrt]) were analyzed using polymerase chain reaction and restriction fragment length polymorphisms to detect polymorphisms previously shown to be associated with resistance. This analysis identified polymorphisms in dhfr at 108-Asn/Thr, 16-Val, and 59-Arg. Polymorphisms in dhps were found less frequently, either 437-Gly alone or paired with 540-Glu. The pfcrt 76-Thr polymorphism was fixed in all parasite populations and pfmdr1 86-Tyr polymorphisms in all populations except in the most eastern regions. The pfmdr1 1042-Asp polymorphism occurred less frequently. These findings indicate that polymorphisms in genes associated with drug resistance in P. falciparum are found across a broad region of Indonesia.     

Epizootic vesicular stomatitis in Colorado, 1982: infection in occupational risk groups

In 1982-1983, an epizootic of vesicular stomatitis occurred in the western United States. Veterinarians, research workers, and regulatory personnel who were exposed to vesicular stomatitis virus were examined for patterns of human infection and prevalence of vesicular stomatitis New Jersey serotype neutralizing antibody. Insight into the mechanism of transmission was sought by comparing activities of antibody-positive and antibody-negative persons. A statistically significant risk factor was a history of infected animals sneezing in the face of serosurvey participants. Elevated odds ratios were also calculated for those who usually examined the oral cavity of affected animals, had open wounds on hands or arms, and had exposure to saliva through the eye or skin. Relatively intimate direct contact was required; a higher risk was associated with examining horses than cattle. Neutralizing antibody prevalence was significantly higher among exposed persons with illness (23%) than in exposed persons without a history of clinical illness (7%). Overall, however, infectivity of VSNJ for humans during the epizootic was low.     

Discovery of Entomophaga maimaiga in North American gypsy moth, Lymantria dispar

An entomopathogenic fungus, Entomophaga maimaiga, was found causing an extensive epizootic in outbreak populations of the gypsy moth, Lymantria dispar, throughout many forested and residential areas of the northeastern United States. This is the first recognized occurrence of this or any entomophthoralean fungus in North American gypsy moths, and its appearance was coincident with an abnormally wet spring. Most fungal-infected gypsy moth larvae were killed in mass during the fourth and fifth stadium and were characteristically found clinging to the trunks of trees with their heads pointed downward. The fungus produces thick-walled resistant resting spores within dried gypsy moth cadavers and infectious conidia when freshly killed larvae are held in a wet environment. The morphology and development of the fungus are described. The fungus appears to have had its origin in Japan, and the current epizootic may have resulted from the survival and inapparent spread of an early introduction in 1910-1911.     

From the stress theory of aging to energetic and evolutionary expectations for longevity

Stress targets energy carriers. Genes for stress resistance are selected that convey high metabolic efficiency enabling adaptation to the energetically restrictive and hence stressful environments of natural populations. Data from experimental organisms and from humans are consistent with a primary role for stress resistance underlying life span, which provides a hitherto neglected procedure for assaying longevity in natural populations. Taking into account the metabolic consequences of stressful environments, the free-radical theory of aging becomes a general stress theory of aging. A recent derivative, the deprivation-syndrome theory of aging, highlights resource and hence energy shortages. Energy balances under the stress theory of aging are primary for an understanding of the evolutionary limits of longevity of organisms in their habitats. In contrast, well-nourished humans of the modern era, and laboratory, domesticated and island populations are exposed to more benign conditions which appear to provide the background for other evolutionary theories of aging, especially the mutation accumulation and antagonistic pleiotropy theories. In modern human populations where selection for stress resistance is relaxed compared with earlier harsher conditions, substantial future evolutionary extensions to maximum life span may be difficult to attain because of the mutation accumulation process. However there is an urgent need for comparative empirical studies of life-history traits including longevity under benign and harsh environments. This revised version was published online in July 2006 with corrections to the Cover Date.     

云南省鼠疫自然疫源地研究(摘要)(英文)

云南鼠疫历史悠久，其来源中外学者多认为输入。新中国成立后经长期调查研究，现完全证明本省鼠疫并非传入而是其本身存在两种不同类型的鼠自然疫源地。1．黄胸鼠鼠疫自然疫源地分布于云南西部、西南部及南部。主要宿主黄胸鼠，主要传播媒介印鼠客蚤，病原体为鼠疫菌滇闽居民区生态型。动物流行病学特点：鼠疫动物病主要存在并流行于海拔400～2100米的平原或宽谷或盆地居民文化景观地带；各月均有发生，但以6～11月较多，高峰在8月；以鼠→蚤→鼠方式传播，以流行和潜在（或微弱）流行方式保持疫源。2．齐氏姬鼠、大绒鼠鼠疫自然疫源地存在于滇西北剑川县山区及其毗邻的丽江、兰坪、云龙、洱源部分山区。主要宿主是齐氏姬鼠和大绒鼠，主要媒介特新蚤指名亚种，病原体为滇西纵谷生态型。动物流行病学特点：鼠疫动物病主要存在并流行于疫源地内海拔2500米以上的云南松林山区耕地景观带；各月均有发生，高峰在4月和12月，表现为双峰型；从年际看，流行有高低潮，大体流行2～3年，缓和1～4年或更长。本文还对黄胸鼠鼠疫疫源地的性质与范围以及黄胸鼠鼠疫疫源地和齐氏姬鼠、大绒鼠鼠疫疫源地的区别与联系进行了讨论。