Arboviruses

            Arboviruses are arthropod-borne viruses, viruses of vertebrates biologically transmitted by blood-sucking insects. They multiply in them, transmitted by bite to vertebrate hosts. Arboviruses  have a very wide host range including many species of animals and birds. The ability to multiply in arthropods is their special characteristic. The most important arbovirus vectors are mosquitoes and ticks. In the laboratory, mice are commonly used for growing arboviruses. They can be grown in the yolk sac or chorioallantoic membrane of chick embryo, in tissue cultures of primary cells like chick embryo fibroblasts, HeLa cells. Most arboviruses agglutinate the red cells of one-day old chicks. Hemagglutination is influenced by pH , temperature etc. Arboviruses are labile, inactivated at room temperature, bile salts, ether.

Adenoviruses

                        Adenoviruses are a group of medium sized, non enveloped, ds DNA viruses that share a common complement fixing antigen. They infect humans, animals and birds, shows strict host specifity. At least 47 serotypes of adenoviruses have been isolated from human sources. Adenovirus infections are common worldwide mostly in children. Many infections are asymptomatic. The virus may persist in the host for many months.It cause infections of the respiratory tract and eyes. These viruses carry DNA up to 7kb and are being investigated as potential vectors in gene therapy.

Spirochaetes

        Elongated, motile, flexible bacteria twisted spirally along the long axis. A charecteristic feature is the presence of endoflagella-polar flagella, situated between outer membrane and cell wall. They are Gram negative of varying sizes. Many are free living saprophytes, while some are obligate parasites. They may be aerobic, anaerobic, facultative. Reproduction by transverse fission. Human pathogens are: Treponema, Borrelia, Leptospira. The spiral shape and serpentine motility of the spirochaetes depend upon the integrity of these endoflagella. Motility is of 3 types : (i) flexion & extension (ii) cork-screw like rotary movement (iii) translatory motion.

Propionibacterium

            Gram positive rod shaped, causes acne.It is most often the result of male sex hormones that stimulates sebaceous glands to increase insize and secrete more sebum. It occurs in both sexes, because the hormones are produced by the adrenal glands as well as by the testes. Microorganisms feed on sebum, and ducts of the glands and  surrounding tissues become inflamed.

Mycobacterium

            Mycobacteria are slender rods, sometimes show branching filamentous forms. In liquid cultures they form a mold-like pellicle, hence the name mycobacteria, meaning fungus-like bacteria. They do not stain readily, but once stained resist decolurisation with dilute mineral acids, therfore they are called “Acid Fast Bacilli” or AFB. They are aerobic, nonmotile, noncapsulated, nonsporing. Generally slow growth, obligate parasites, opportunistic pathogens and saprophytes.

Haemophilus

            Small, non-motile, non-sporing, Gram-negative bacilli that are parasitic on human beings and animals.  They are characterized by their requirement of one or both of two accessory growth factors present in blood, ie., X and V.  It was isolated in 1892 by Pfeiffer, hence known as Pfeiffer's bacillus. The genus name is derived from the Greekwords meaning 'blood loving'. H. influenzae is an exclusively human pathogen whose complete genome has sequenced. The important  species are   Haemophilus influenzae, H. aegyptius, H. ducreyi

Corynebacterium

            Corynebacteria are Gram positive, non-acid fast, non-motile rods. They frequently show club-shaped swellings and hence the name, ‘coryne = club’. The most important genus is C. diphtheriae, causative agent of diphtheria.