Infectious DiseasesImmunology LATG: Chapters 10-11
Health Maintenance • Maintaining lab animal health requires • Proper environment. • Proper food and water. • Disease prevention program. • Disease detection program. • Contingency plan if disease is detected.
Disease Prevention • Type of program depends upon species. • Rodents--primarily review of vendor data and procedures in place to prevent introduction and spread of disease. • Nonrodents--As for rodents but may also have other facets such as vaccinations, dewormings etc.
Disease Detection • Like NORAD, PADDS (Pfizer Animal Disease Detection System) relies on • Early warning system--technicians who check animals daily. • Early response--veterinary technicians who evaluate reported problems. • Final response--delivered after evaluation and consultation with veterinarian and PI.
Disease Detection • A rodent sentinel program is in place to screen for potential viral, bacterial and parasitic contaminants. • In the rare instance of an actual infection steps are taken to evaluate the extent of the infection and eliminate it.
Pathogenic Organisms • Life forms that have the potential to cause disease under the proper conditions. • Text classifications • Bacteria • Fungi • Viruses • Parasites
Biology Influencing Organisms • In laboratory animal science we are also very concerned with biology influencing organisms. • These organisms may or may not cause clinical disease. • Biological systems can be influenced even by subclinical infections.
Viruses • Small particles made up of nucleic acid and a protein capsule. • Viruses may also be covered by an envelope • Many viruses can infect laboratory animals, most do not cause clinical disease. • Viruses are divided into two main classes. • DNA viruses • RNA viruses
DNA Viruses of Mice • Mousepox (Ectromelia) • Minute virus of mice • Cytomegalovirus • Polyoma virus • Mouse parvo virus
DNA viruses of rats • Polyoma virus (in nude rats) • Adenovirus • Kilham rat virus • Rat parvo virus
RNA viruses of mice • Mouse hepatitis virus (MHV) • Sendai • Lymphocytic choriomeningitis • Reovirus • Hantavirus • Retroviruses--mouse leukemia virus and mouse mammary tumor virus
RNA viruses of rats • Sialodacryoadenitis virus (SDAV) • Sendai • Pneumonia virus of mice • Hantaan virus
Bacteria • Many bacteria in nature are beneficial. • In nearly all mammals there are more bacterial cells than mammalian cells • Consist of a cell membrane, a cell wall and cytoplasm.
Bacteria • Classified by • Morphology • Size • Staining characteristics • Formation of spores • Nutrient requirements • Biochemical reactions • All are prokaryotes
Bacterial Morphology • Cocci (spherical) • Pairs--Diplococci • Chains--Streptococci • Clusters--Staphylococci • Rods, may be straight or slightly curved • Spiral shaped
Bacterial Staining Characteristics • Classified into Gram negative and Gram positive groups • Gram positive--dark blue/violet stain, due to a thick cell wall • Gram negative--red stain, due to a thin cell wall with high lipid content
Fungi • Many fungi in nature are beneficial • Used to make • bread • beer • wine • antibiotics • A few fungi are pathogenic • All are eukaryotes
Beneficial fungus • Saccharomyces cervisae
Fungi • Pathogenic species classified into • Superficial mycoses • Systemic mycoses
Superficial mycoses • Infect superficial tissues; skin, hair and nails. • Commonly called “ringworm” • See scaliness and alopecia (hairloss), sometimes redness
Systemic mycoses • Infect deep tissues; lung, bone, CNS, GI tract. • Often associated with certain geographic areas • Lower Sonoran desert--Coccidioides immitis • Central and southeastern US--Blastomyces spp.
Parasites • Large group of single cell (protozoans) and multi-cell (metazoans) animals which must coexist on another animal during some part of their life cycle • A parasite must also have the potential for causing disease in the host
Parasites • Websites of interest • Parasites and Parasitological Resources • http://www.biosci.ohio-state.edu/~parasite/home.html • Identification and Diagnosis of Parasites of Public Health Concern • http://www.dpd.cdc.gov/DPDx/Default.htm
Parasite Lifecycles • “If you know the enemy and know yourself, you need not fear the result of a hundred battles.” Sun-tzu, “The Art of War” • Knowing the life cycle of a parasite is the key to knowing how to prevent and treat infestation.
Parasite Lifecycles • Life cycles can be direct or indirect. • Direct--parasite eggs/larva can infect definitive host • Indirect--parasite needs to pass through an intermediate host prior to infecting the definitive host
Parasite Hosts • Definitive host--the species of animal responsible for housing the reproductive stage of the parasite • Intermediate host--the species of animal responsible for housing any of the non-reproductive stages of the parasite • Disease can occur in both types of host
Protozoan Parasite • Amoebas • Flagellates • Ciliates • Sporozoa
Toxoplasma gondii • A sporozoan parasite • Definitive host--cat • Intermediate host--almost any other mammal or bird • Causes self-limiting diarrhea in cats • May cause severe disease in immunosuppressed intermediate host
Toxoplasma gondii • Trophozoites in lung fluid from an HIV-infected person • Tissue cyst from a cat
Other protozoa • Giardia • Trypanosome
Metazoan Parasites • Trematodes--Flukes • Cestodes--Tapeworms • Nematodes • Arthropods--insects, ticks, mites
Cestodes--Tapeworms • Parasites which inhabit the GI tract of the definitive host • May cause lesions in many different tissues in the intermediate host • Do not have their own digestive system • Life cycle often indirect but may also be direct
Tapeworm tissue cysts Cysts in a baboon heart
Hymenolepis (Rodentolepis) nana • A tapeworm of rodents and humans • Has a direct life cycle
Nematodes--The “Roundworms” • Worms that are round in cross-section • Body structure contains a GI tract as well as reproductive organs • Both direct and indirect life cycles • May live in many tissues in both the intermediate and definitive hosts
Ascarids • Common intestinal parasite of dogs, cats, swine and humans • Also called roundworms • Both direct and indirect life cycles • Infections in humans can result in visceral larval migrans or ocular larval migrans
Toxocara canis • Adults • Egg
Dirofilaria immitis Heartworm • A nematode parasite that lives in the right side of the heart in dogs and occasionally cats • Life cycle of this parasite requires passage through mosquitoes • Infection can cause heart failure
Acanthocephalans • Thorny headed worms • Seen in pigs and nonhuman primates
Arthropod parasites • Large group of external parasites that include • Insects • Ticks • Mites
Arthropod parasites • In lab animal science most likely to see • Mites • Lice • Fleas
Mites • Parasites in the arachnid family • Have eight legs in the adult stage • Live on the skin, sometimes deep in the hair follicle • May be zoonotic
Sarcoptic mange mite • Sarcoptes scabiei with multiple subspecies • Infest a multitude of species • Infestation is also called “scabies” • Can cause intense pruritis • Infestation is worse if animal is immunosuppressed
Prevention of Infectious Disease • In all cases it’s easier to prevent diseases than to treat them • Principles of prevention are simple and usually more cost-effective than treatment