Plague in camels and goats: their role in human epidemics

Plague: past, present, and future

The authors argue that plague should be taken much more seriously by the international health community.

Clinicopathologic aspects of animal and zoonotic diseases of bioterrorism

We live in an era of emerging infectious diseases and the threat of bioterrorism. Most of the infectious agents of modern concern, from plague to avian influenza H5N1, are zoonotic diseases: infectious agents that reside in quiet animal reservoir cycles that are transmitted occasionally to humans. The public health, health care, and veterinary communities have an enormous challenge in the early recognition, reporting, treatment, and prevention of zoonotic diseases. An intimate understanding of the natural ecology, geographic distribution, clinical signs, lesions, and diagnosis of these diseases is essential for the early recognition and control of these diseases.

Animals as sentinels of bioterrorism agents

Pets, wildlife, or livestock could provide early warning.

We conducted a systematic review of the scientific literature from 1966 to 2005 to determine whether animals could provide early warning of a bioterrorism attack, serve as markers for ongoing exposure risk, and amplify or propagate a bioterrorism outbreak. We found evidence that, for certain bioterrorism agents, pets, wildlife, or livestock could provide early warning and that for other agents, humans would likely manifest symptoms before illness could be detected in animals. After an acute attack, active surveillance of wild or domestic animal populations could help identify many ongoing exposure risks. If certain bioterrorism agents found their way into animal populations, they could spread widely through animal-to-animal transmission and prove difficult to control. The public health infrastructure must look beyond passive surveillance of acute animal disease events to build capacity for active surveillance and intervention efforts to detect and control ongoing outbreaks of disease in domestic and wild animal populations.

Plague from eating raw camel liver

We investigated a cluster of 5 plague cases; the patients included 4 with severe pharyngitis and submandibular lymphadenitis. These 4 case-patients had eaten raw camel liver. Yersinia pestis was isolated from bone marrow of the camel and from jirds (Meriones libycus) and fleas (Xenopsylla cheopis) captured at the camel corral.

Yersinia pestis as a telluric, human ectoparasite-borne organism

The classic epidemiological model of plague is an infection of rodents that is transmitted to human beings by rodent ectoparasites. This model fits with observations of sporadic and limited outbreaks, but hardly explains the persistence of plague foci for millennia or the epidemiological features drawn from the descriptions of historical pandemics. A comprehensive review of the published data, including scientific papers published in France between 1920 and 1940, allows the completion of the epidemiological chain by introducing soil as a reservoir, burrowing rodents as a first link, and human ectoparasites as the main driving force for pandemics. Modern studies are needed to confirm the validity of this controversial model and to assess the relative contribution of each link in the various epidemiological presentations of plague. If confirmed, these data should be taken into account to update public-health policies and bioterrorism risk management, particularly among ectoparasite-infested people.

A 12-case outbreak of pharyngeal plague following the consumption of camel meat, in north-eastern Jordan

Between late January and early February 1997, an outbreak of plague, associated with cervical lymphadenopathy and fever, occurred in the Jordanian village of Azraq ad-Druze, which lies about 50 km west of the border with Saudi Arabia. The 12 cases who presented at hospital were initially assumed to have tularaemia, and all were successfully treated with gentamicin. When, however, their sera were tested for evidence of Yersinia pestis or Francisella tularensis infection (using haemagglutination, enzyme immuno-assays for specific IgM or the F1 antigen of Y. pestis, and micro-agglutination tests), all 12 were found to have anti-Y. pestis IgM. Three dogs shot near the Saudi Arabian border were also found seropositive for antibodies against Y. pestis. Eleven of the 12 patients reported that, 2-4 days before their symptoms appeared, they had eaten the meat cut from the carcass of the same camel, either raw (10 cases) or cooked (one case). All 12 patients were diagnosed as cases of pharyngeal plague (the first cases of plague reported in Jordan for more than 80 years), caused by Y. pestis that most had acquired when they ate raw meat from a camel that was infected with the pathogen.

Intraspecific diversity of Yersinia pestis

Increased interest in the pathogenic potential of Yersinia pestis has emerged because of the potential threats from bioterrorism. Pathogenic potential is based on genetic factors present in a population of microbes, yet most studies evaluating the role of specific genes in virulence have used a limited number of strains. For Y. pestis this issue is complicated by the fact that most strains available for study in the Americas are clonally derived and thus genetically restricted, emanating from a strain of Y. pestis introduced into the United States in 1902 via marine shipping and subsequent spread of this strain throughout North and South America. In countries from the former Soviet Union (FSU), Mongolia, and China there are large areas of enzootic foci of Y. pestis infection containing genetically diverse strains that have been intensely studied by scientists in these countries. However, the results of these investigations are not generally known outside of these countries. Here we describe the variety of methods used in the FSU to classify Y. pestis strains based on genetic and phenotypic variation and show that there is a high level of diversity in these strains not reflected by ones obtained from sylvatic areas and patients in the Americas.

Expression of heterologous O-antigen in Yersinia pestis KIM does not affect virulence by the intravenous route

All strains of Yersinia pestis examined have been found to lack an O-antigen. In other members of the Enterobacteriaceae, the rough phenotype often results in attenuation. However, Y. pestis is the aetiological agent of bubonic plague. In evolving from the ancestral enteropathogenic Yersinia pseudotuberculosis, and with the development of an arthropod-vectored systemic pathogenesis, smooth LPS production is not necessary for Y. pestis virulence and the metabolic burden has been alleviated by inactivation of the O-antigen biosynthetic operon. To investigate this, Y. pestis strain KIM D27 was transformed with a plasmid carrying the operon encoding the O-antigen of Yersinia enterocolitica O : 3. Expression of the O-antigen could be detected in silver-stained gels. The receptor for bacteriophage phiYeO3-12 has been shown to be O-antigen, and infection by this bacteriophage results in lysis of Y. enterocolitica O : 3. Expression of the O-antigen in Y. pestis conferred sensitivity to lysis by phiYeO3-12. The O-antigen-expressing clone was shown to be as virulent in mice by the intravenous route of challenge as the rough wild-type. Assays showed no alteration in the ability of Y. pestis to resist lysis by cationic antimicrobial peptides, serum or polymyxin.

Involvement of dogs in plague epidemiology in Tanzania. Serological observations in domestic animals in Lushoto District

Venous blood was collected aseptically from clinically healthy domestic dogs, goats, sheep, cats and fowl in various plague-infected villages of Lushoto District, Tanzania, at the time when the disease was actively prevalent in the area. Flea ectoparasites were collected from the animals, processed, identified and counted. Serum samples were tested for specific plague antibodies, using the passive haemagglutination technique and checked by passive haemagglutination inhibition tests. Altogether 389 animals, of which 201 were domestic dogs, were involved. 11 (5.5%) dogs had significantly elevated specific plague antibodies at titres ranging from 20 to 1280. All the dogs were also heavily infested with fleas at a mean index of 7.7 fleas per animal. Of 1,871 fleas collected from the dogs, 93.8% were Ctenocephalides felis and 6.2% were C. canis. All the other animals examined were negative for plague. It was concluded that domestic dogs could play an important role as plague carriers in the area and that the animals could serve as sentinel animals for the detection of plague in villages where human plague outbreaks have not previously occurred.

Experimental Yersinia pestis infection in rodents after intragastric inoculation and ingestion of bacteria

To clarify the pathogenesis of oral plague infection, we studied the susceptibility of three species of rodents to intragastric inoculation of Yersinia pestis, described the pathology and progression of infection, and measured antibody responses to fraction IA antigen of Y. pestis. The 50% lethal doses of bacteria by intragastric inoculation for Mus musculus, Zygodontomys pixuna, and Rattus rattus were log10 = 6.32, 5.46, and 9.62, respectively, which were at least 1,000-fold higher than the values obtained by subcutaneous inoculation. M. musculus was shown to be susceptible to lethal infection also when bacteria were ingested in drinking water. Microscopic pathology was consistent with heavy systemic infection. Quantitative cultures of tissues at different times after intragastric inoculation revealed that infections of blood, liver, and spleen preceded infections of Peyer's patches and mesenteric lymph nodes. Stool cultures were negative. The strain of Y. pestis used for inoculation was killed when exposed to a buffered solution at pH less than or equal to 3. Antibody responses were observed in some of the surviving rodents after intragastric challenge. These results showed that Y. pestis was an effective oral pathogen that produced fatal systemic infections and self-limited infections with immunity but did not produce enteric pathology or lead to fecal excretion of bacteria.