Animal models--a neglected medical resource

Whipple's disease and "Tropheryma whippelii"

Whipple's disease is a rare bacterial infection that may involve any organ system in the body. It occurs primarily in Caucasian males older than 40 years. The gastrointestinal tract is the most frequently involved organ, with manifestations such as abdominal pain, malabsorption syndrome with diarrhea, and weight loss. Other signs include low-grade fever, lymphadenopathy, skin hyperpigmentation, endocarditis, pleuritis, seronegative arthritis, uveitis, spondylodiscitis, and neurological manifestations, and these signs may occur in the absence of gastrointestinal manifestations. Due to the wide variability of manifestations, clinical diagnosis is very difficult and is often made only years or even decades after the initial symptoms have appeared. Trimethoprim-sulfamethoxazole for at least 1 year is usually considered adequate to eradicate the infection. The microbiological diagnosis of this insidious disease is rendered difficult by the virtual lack of culture and serodiagnostic methods. It is usually based on the demonstration of periodic acid-Schiff-positive particles in infected tissues and/or the presence of bacteria with an unusual trilaminar cell wall ultrastructure by electron microscopy. Recently, the Whipple bacteria have been characterized at the molecular level by amplification of their 16S rRNA gene(s). Phylogenetic analysis of these sequences revealed a new bacterial species related to the actinomycete branch which was named "Tropheryma whippelli." Based on its unique 16S ribosomal DNA (rDNA) sequence, species-specific primers were selected for the detection of the organism in clinical specimens by PCR. This technique is currently used as one of the standard methods for establishing the diagnosis of Whipple's disease. Specific and broad-spectrum PCR amplifications mainly but not exclusively from extraintestinal specimens have significantly improved diagnosis, being more sensitive than histopathologic analysis. However, "T. whippelii" DNA has also been found in persons without clinical and histological evidence of Whipple's disease. It is unclear whether these patients are true asymptomatic carriers or whether differences in virulence exist among strains of "T. whippelii" that might account for the variable clinical manifestations. So far, six different "T. whippelii" subtypes have been found by analysis of their 16S-23S rDNA spacer region. Further studies of the pathogen "T. whippelii" as well as the host immune response are needed to fully understand this fascinating disease. The recent cultivation of the organisms is a promising major step in this direction.

A perspective on the selection of experimental models

We are entering an age when advances in biotechnology, greater communication among teams of scientists using multiple model systems, and the power of the computer will dwarf the great advances of the mid-20th century. Advances in medicine rest largely on the use of models of biological systems, including animal models. Model systems used by most biomedical scientists can be considered in four categories: theoretical, in vitro, nonmammalian and mammalian. Each category has advantages and limitations in describing the dynamic milieu of events that characterize human biologic response. Although individual models can be good predictors, multiple models are better than single models; the most critical drawback is lack of human information for comparison. The scientific community must improve the methodologies necessary to extrapolate data from the various model systems to the human, because these model systems are the foundation of discovery in biomedicine and the bedrock upon which to base valid risk assessments. It is vital that we communicate the importance of these techniques to the general public. Advances in science and improved quality of life for the human race depend on these principles.

Use of Epidemiological and Toxicological Observations in Domestic and Wild Animal Populations for Evaluating Human Health Risks

Domesticated and wild animal populations are important resources in evaluating human health risks. Animals not only share man's environment, but some of them are also part of the human food chain. Three examples of monitoring the health of animal populations and using these data in evaluating human health risk were reviewed.

A study of horses, cattle and wildlife in a Missouri lead mining and smelting area revealed that horses were sensitive indicators of environmental lead contamination; they developed clinical signs of lead poisoning and died, while other animal species in the same area did not exhibit signs of illness. Although they did not appear ill, cattle in the same area had liver and kidney lead concentrations that were higher than tolerance levels established in England, Wales and Canada. Wildlife such as bullfrogs, muskrats, and greenbacked herons collected downstream from an old lead mining area had significantly higher lead and cadmium levels than either upstream samples or comparable downstream samples collected at a new lead mining area. Some of these data were used in a court trial which resulted in the lead company buying the farmland so that humans and domestic animals would not be exposed.

Another study of municipal sludge application on Ohio farms did not reveal excess illness rates for either livestock or humans living on farms receiving the sludge, as compared with those on control farms. However, cattle were more sensitive than humans as early indicators of low level exposure to toxic heavy metals such as cadmium and lead. Also, calves on sludge-receiving farms accumulated cadmium and lead in their kidneys.

The National Animal Health Monitoring System (NAHMS), currently in a pilot stage in eight states, is another example of the use of animal populations to evaluate human health risk. Information from NAHMS about zoonotic infections, use of drugs in food producing animals and diseases common to both animals and man, provide a better understanding of human disease. Population-based animal studies are desirable adjuncts to laboratory animal studies in assessing human health risk due to environmental exposure.

Causes of windowing-induced dysmorphogenesis (neural tube defects and early amnion deficit spectrum) in chicken embryos

Previous reports suggest that windowing the shells of chicken eggs during the first day of incubation frequently results in dysmorphogenesis of the central nervous system. We report here data that further delineate the neural tube defects associated with this animal model. In addition, we describe another birth defect syndrome associated with windowing: the early amnion deficit spectrum (EADS). Several components of the egg are altered structurally by windowing: the shell, outer and inner shell membranes, yolk, and air space at the blunt end of the egg. A new air space is formed over the embryo as the original one at the blunt end is obliterated. A series of studies (pH, oxygen and carbon dioxide tensions, relative humidity, temperature, and deformation of the yolk documented with magnetic resonance imaging) examining individual steps of the windowing procedure and additional techniques that stimulate windowing suggest that mechanical stress causes isolated neural tube defects and dehydration causes amnion defects. These amnion defects are associated with other embryonic abnormalities suggestive of deformations consistent with EADS.

Inherited metabolic disease in laboratory animals: a review

Research on the screening for and study of animal models of inherited metabolic disease is reviewed. It is emphasized that an animal model, to be of value, must be an inherited deficiency of the same enzyme as the one deficient in the human syndrome. If this criterion is adhered to there is a remarkable identity in aetiology between animal and man. Specific examples of inherited metabolic disease in laboratory animals are described for: amino acid metabolism; lysosomal storage diseases, carbohydrate metabolism, transport disorders and trace element metabolism; the mutants found in mice being the easiest to manipulate biochemically and genetically. There is still a lack of adequate screening programmes for animal homologues of the more serious human inborn errors (such as lysosomal storage diseases) where laboratory studies could provide significant advances in therapy.

Hypophosphatemia: mouse model for human familial hypophosphatemic (vitamin D-resistant) rickets

A new dominant mutation in the laboratory mouse, hypophosphatemia (gene symbol Hyp), has been identified. The Hyp gene is located on the X-chromosome and maps at the distal end. Mutant mice are characterized by hypophosphatemia, bone changes resembling rickets, diminished bone ash, dwarfism, and high fractional excretion of phosphate anion (low net tubular reabsorption). Phosphate supplementation of the diet from wearning prevents the appearance of severe skeletal abnormalities. The hypophosphatemic male mouse resembles human males with X-linked hypophosphatemia and the Hyp gene is presemably homologous with the X-linked human gene. The mouse model should facilitate study of the defect in transport of plasma inorganic phosphate anion.

[Biochemical parameters of blood plasma, and body and organ weights of Wistar rats with dietarily-induced experimental obesity]

The authors investigated in rats with dietarily-induced obesity certain biochemical parameters of the blood plasma as well as body and organ weights during the dynamic and the static phase of obesity development. They determined total cholesterol, total protein, albumin, creatinine, urea nitrogen and transaminases. After 4-5 weeks, the animals on a high-diet (50% of fat) had body weights which were, on an average, by 90% higher than those of the control animals. This difference persisted during the static phase. In the animals on a high-fat diet, body length was greater. The high-fat diet (which contains a great proportion of sunflower oil) leads to a decrease of the plasma cholesterol level in obese rats. The plasma-protein bodies, creatinine and urea nitrogen values as well as those for transaminases permit, as parameters for function and damage, to draw conclusions as to kidney and liver damages in the animals on high-fat diet. There were no differences in plasma protein between the control and experimental animals. On the contrary, obese rats showed in some cases high creatinine concentrations during the dynamic phase. Differences in urea nitrogen were not observed between the two groups of animals. Increases in alanine aminotransferase were found in the animals on high-fat diet as a manifestation of fatty degeneration of the liver. A synopsis of weight curves, biochemical parameters and histological findings permits the conclusion that, besides of dietarily-induced metabolic alterations, no additional organic lesions occurred during the present animal experiment on dietarily-induced obesity.

Ulcerative colitis in apes: A comparison with the human disease

The pathological changes in the colons of two young gorillas and an adult orang-utan which developed diarrhoea and died, are described. Since no causative agents could be identified and the changes were indistinguishable from the active phase of ulcerative colitis in humans, these cases were considered examples of this disease in apes. Evidence of early healing was found in one case and the suitability of apes and monkeys as possible animal models of the human disease is discussed.