U PDATEEndangeredIncluding a Reprint Species of theTechnical latest USFWS Bulletin THE UNIVERSITY OF MIC'HI(;,Zlri July 1989 Vol . 6 No. 9 School of Natural Resources In this issue: Infectious Three Mammals and Diseases and Two Plants Listed Endangered Species Management Agriculture, Wetlands and Endangered U.S. Bans Ivory Species: The Food Imports Security Act Infectious Diseases and Endangered Species Management by Andrew Dobson and Dan Miller Disease can play a pivotal role in standing of the types of pathogens that macroparasites (Anderson and May the population dynamics of endangered pose a threat to endangered popula- 1979). Microparasites include viruses, species. The mountain gorillas of tions. Several important general prin- bacteria, fungi, and many protozoans; Virunga recently suffered an epidemic ciples have emerged from the resur- these pathogens are characterized by of respiratory illness which infected an gence of interest in the ecology of para- their small size (invisible to the naked estimated ten percent of the population sites and disease of the last decade eye), their ability to reproduce directly and led to the death of six gorillas (Anderson and May 1979, May 1988, in infected hosts, and their ability to (Sholley 1989). The causative patho- Scott and Dobson 1989). The greatest induce sustained immunity to reinfec- logical agent was identified as measles, level of sophistication and detail is tion in their hosts. Macroparasites, presumably introduced through contact available for models of infectious dis- which include the parasitic helminths, with an infected human. Luckily an eases in human populations, where ticks, and fleas, are characterized by inoculation campaign was quickly mathematical models have become in- their larger size (visible to the naked mounted, and large scale vaccination of creasingly prominent as tools for the eye), and their relative inability to re- potentially susceptible individuals pre- study of disease dynamics. Many of the produce directly within infected hosts. vented a full epidemic. In a less fortu- important epidemiological features of This classification makes sense nate incident, North Sea populations of these models can be applied to systems when the characteristic patterns of the harbour seals (Phoca vitulinu) were where less comprehensive data are two types of infection are considered. struck by a viral epidemic last summer available. Essentially, hosts acquire macropara- which led to the deaths of more than sites as discrete numbers of infective 14,000 animals (Anon 1989). Such larvae which give rise to an infrapopu- epidemics are not confined to verte- Types of Pathogens lation of adult parasites in each infected brates. Crayfish plague, a disease host; these parasites induce a limited caused by a fungal pathogen, threatens Parasites and pathogens can be immune response in the host that may the endangered whiteclawed crayfish conveniently classified on epidemiol- diminish the rate of acquisition of sub- (Austropotamobius pallipes) in its last ogical grounds as microparasites and sequent challenge infections. In con- stronahold in the lakes of central trast, microparasites tend to infect Ireland (Reynolds 1988). These examples suggest that an understanding of the population dynamics of pathogens, and the diseases they cause, is essential to the management of populations of both endangered and apparently healthy populations. In this short review we outline some important features of the population biology of infectious diseases and discuss their implications for the conser- vation of endangered populations, The dynamics of parasites and pathogens are intrinsically diffi- cult to study in endangered species because of small population sizes and the concern for protecting the remaining populations of a spe- cies. However, studies on non- endangered species can be used as a means of gaining a basic under- black-footed ferret (Mustella nigripcs) M.Wa through the lifetime of a mature 1 Endangered Species UPDATE Vob 6 No. 9 female in the absence of density de- population is disturbed or stressed; pendent consmints (Anderson and May these outbreaks may reduce the popula- 1982b). In both cases, R, must be equal tion to sizes where demographic sto- to or greater than one in order for the in- chasticity or AUee effects prevent re- fection to persist. NT is the threshold covery, Such effects may be com- Endangered Species density of susceptibles required for a pounded by increased levels UPDATE disease to establish in a population. R, of aggression in high density popula- and N, generally have an inverse rela- tions, which in turn reduce levels of A forum for information exchange on immunocompetence. example, in a endangered species issues tionship; if R, is large, then a smaller NT o or July 1989 is required for establishment of a pathu- captive population of macaques Vd. 6 No. 9 gen. Thus, particularly virulent species (Macaca mulatta), clinically confirmed require large populations to sustain tetanus accounted for approximately 25 percent of the 230 deaths which oc- Rob Bbir.,................. Editor them; when a pathogen species is highly Suzanne Jones ...... ......Assistant Editor specific towards its host species, it is curred during a five-year study (Rawl- unlikely to be the ultimate cause of ins and Kessler 1982). The tetanus extinction in an endangered population, organism, which is found in the feces of Instructions for Authors: because the pathogen itself is likely to infected animals, enters the body The Endongend Species UPDATE become extinct when host population through puncture wounds, postpartum welcomes articles related to species density falls below N, through host contamination of the uterus, or umbili- protection in a wide range of areas in- mortality or reductions in fecundity cal infections. Peak levels of annual cluding but not limited to: research and management activities for endangexd (Dobson and May 1986,1989). mortality occurred during the mating species, theoretical approaches to season when levels of aggression were species conservation, and habitat protec- at a peak and infection could occur tion and preserve design. Book reviews, Pathogens As A Threat to Endan- through septic wounds. editorial comments, and announcements of current events and publications are gered Species also welcome. One characteristic of most endan- Diseases That infect Multiple Readers include a broad range of gered species is small population sizes. Host Species professionals in both scientific and policy fields. Anicles should be written These small populations are often found in an'easily understandable style for a at artificiallyhigh densities in reserves, Pathogens that can utilize a range knowledgeable audience. thereby often facilitating the rapid of host species present the greatest Manuscripts should be 10-12 double spread of pathogens that may be intro- threat to endangered species. The pres- spaced typed pages. For further information please contact Rob Blair at duced into these populations, even if the ence of reservoir host species allows the number listed below. population density is below the thresh- generalist pathogens to establish and old density required to maintain an maintain infections in populations oth- Subscription Informafion: endemic infection. A classic example erwise too small to sustain them (Dob- The Endangered Species UPDATE is published approximately ten times per of this effect may be the outbreak of son and May 1989). Where the pathu- year by the School of Natural Resources canine distemper that nearly eradicated gen is more virulent towards rarer spe- at 'Ihe University of Michigan. Annual the black-footed ferret (Mustella ni- cies, extinction of a susceptible popula- subscriptions are $15 each ($18 outside gripes) shortly after its rediscovery in the U.S.). Send check or money order tion may be facilitated by the presence (made payable to 'Ihe University of 1981 near Meeteetse in Wyoming of a more common coexisting host. In Michigan) to: (Thome and Williams 1988). The free- many cases the impact of the pathogen. ranging ferret population, which results from differences in the lengths Endangered Species UPDATE School of Natural Resources peaked at 129 individuals in 1984, was of time for which the various host spe- The University of Michigan reduced to six individuals by the end of cies have had to develop a resistance to Ann Arbor, MI 48109-11 15 1985 by an epizootic of the disease the pathogen. The establishment of (3 13)763-3243 (Forrest et al. 1988). pathogens of this type is often the result Where small populations have re- of the induction of a non-native host duced genetic variability due to past species which acts as a reservoir for the Cover: bottleneck effects and inbreeding, the disease while remaining comparatively Elk (Cervus elaphus catdensir) loss of genetic diversity at such loci as immune to it. A classic example of this the major histocompatibility complex type of introduction has occurred in Photo: Colorado Department of Natural and other immune system loci may in- Hawaii where the extinction of several Resources, Wildlife Division crease population susceptibility to a species of endemic landbirds was facili- The views expressed in the Endangered disease epidemic (Allendorf 1986, tated by the induction of a suitable Species UPDATE are those of the author O'Brien and Evermann 1988). Simi- vector for transmissions of avian ma- and may not necessarily reflect those of the U.S. Fish and Wildlife Service or larly, epidemics often break out when a laria The pathogen had little impact on The University of Michigan. Vol. 6 No. 9 Endangered Species UPDA TE Table 1. Tactics taken in pathogen control may depend on the primary host More complex problems arise when elk feed alongside cattle during the period that abortions are occurring, Wild Host Domestic Host thus providing a potential source of in- fection for brucellosis-free cattle herds. Circumstantial evidence has implicated Reservoir Controlled culling of Control is likely if elk in two cases of brucellosis arising in Host wild host often seen economic losses in cattle in northwestern Wyoming as cheapest viable domestic animals (Boyce 1989, Tessaro 1986).