Shiga Toxins of Escherichia coli

Shigella dysenteriae type 1 causes bacillary dysentery and produces the classical Shiga toxin (Stx). Some pathogenic E. coli that produce disease in humans or animals produce toxins (currently designated Stxl and Stx2) that are closely related to Stx. These E. coli Shiga toxins were previously called Shiga-like toxins (SLT) or Vero toxins (VT). E. coli that cause hemorrhagic colitis and hemolytic uremic syndrome in humans (enterohemorrhagic E. coli EHEC ) typically produce moderate to large...

Fungal Transmission Mechanisms

Two types of fungal vector relationships are recognized in vitro and in vivo. They are distinguished by the method of acquisition of the virus by the fungus and the location of the virus relative to the fungal resting spore (internal or external). In in vitro transmission the virus is carried externally on the zoospores (Fig. 2) and virus is not found within resting spores. In in vivo transmission, virus is acquired during growth of the fungus in a virus-infected plant and is found within...

Clinical Features of Infection

HSV infects neonates, children and adults. It produces a wide spectrum of diseases ranging from mild illness, undiscernible in the majority of patients, to severe and life-threatening disease in relatively few patients. The incubation period is 1-26 days (median 6-8 days). Factors that influence severity are age, gender, host genetic factors, immune competence, associated illnesses, and virulence of the infecting virus strain. Most (70-90 ) childhood HSV-1 infections are asymptomatic, but they...

Recombination in DNA Viruses

Recombination in many DNA viruses is believed to be accomplished by cellular enzymatic activities. There are two general types of genetic DNA recombination in the cell homologous recombination (general recombination) and nonhomologous recombination. Nonhomologous or site-specific recombination occurs relatively rarely and requires special proteins that recognize specific DNA sequences to promote recombination. Homologous recombination occurs between two DNA sequences that are the same or very...

Pathology and Pathogenesis

Enlarged peripheral nerves are present in almost all chickens with clinical signs of classical MD and in many with the acute form of the disease (Fig. 2). Figure 5 Lymphoid cell infiltration in peripheral nerve of a chicken with Marek's disease. (From Payne (1972), in Oncogenesis and Herpesviruses, Biggs, P.M., de The, G., and Payne L.N. (eds), pp. 21-37, IARC Scientific Publications No. 2, International Agency for Research on Cancer, Lyon, with permission.) Figure 5 Lymphoid cell infiltration...

Yeast RNA Replicons

Four completely distinct RNA to RNA replication systems have been found in various strains of S. cerevisiae L-A and its satellites (including M), L-BC, 20S RNA and 23S RNA. The L-A and L-BC systems are encapsidated, whereas the 20S and 23S RNAs apparently replicate naked in the cells (Table 1). None of the viruses are known to have a natural extracellular infectious cycle, although they can be introduced into spheroplasts along with transforming DNA plasmids. All are efficiently transmitted...

Some Common Zoonotic Viruses Around the World

Viral zoonotic diseases occur on every continent except, perhaps, Antarctica. Some are found around the world, in a variety of ecological settings. Others are found only in very limited ecologic and geographic foci. The panorama of viral zoonotic diseases is constantly changing. Although hundreds of viruses have been shown to infect both humans and animals, the importance of many of these viruses, as agents of either human or animal disease, has not yet been established. Some of the more...

Pathology and Histobiology

Laboratory infection of ducklings or older birds can produce a variable degree of hepatic injury, usually mild, including portal hepatitis with penetration of the limiting plate by mononuclear lymphoid cells and, occasionally, lobular hepatitis. Portal hepatitis, by itself, is quite common in domestic ducks, irrespective of exposure to duck hepatitis B virus, whereas a periportal or lobular hepatitis can be correlated with experimental viral infection. Piecemeal and focal necrosis have also...

Prevention and Control of Dengue

The options available for prevention and control of DEN DHF are limited. Although currently not available, considerable progress has been made in recent years in development of a vaccine for dengue DHF. Effective vaccination to prevent DHF will require a tetravalent, live attenuated vaccine. Promising candidate attenuated vaccine viruses have been developed and have been evaluated in phase I and II trials in Thailand. A commercialization contract has been signed and the tetravalent vaccine...

Clinical Features Lassa fever

Lassa fever begins after 7-18 days of incubation, with fever, headache and malaise. Aching in the large joints, pain in the lower back, a nonproductive cough, severe headache and sore throat are common. Many patients also develop severe retrosternal or epigastric pain. Vomiting and diarrhea occurs in between a half and two-thirds of patients. In more severely ill patients complete prostration may occur by the 6th to 8th day of illness. Patients with Lassa fever appear toxic and anxious, and in...

Astroviruses Astroviridae

These viruses have a diameter of 28-30 nm and possess a positive-strand RNA genome coding for four structural polypeptides. A surface structure with a five- or six-pointed star-like appearance (hence Figure 5 Astroviruses. Bar 100 nm. Figure 5 Astroviruses. Bar 100 nm. astrovirus) can be seen by electron microscopy on 5 10 of particles (Fig. 5). These viruses were first described in association with an outbreak of mild diarrhea in newborn infants. Strains have been identified in many animals...

Vaccination

During the 1930s attenuated rinderpest vaccines were developed by passage of the virus in nonnatural hosts, e.g. rabbit and embryonated eggs (lapinized avian-ized) or goats (caprinized). The Japanese lapinized avianized vaccine was used extensively to control the disease in Asia. In India and Africa the caprinized virus was used however, this virus was not completely attenuated and it may have been responsible for the circulation of rinderpest in small ruminants in India. In the early 1960s the...

Two Main Requirements of a Vaccine

The safety of a candidate vaccine has become of prime importance. Most of the vaccines listed in Table 1 are very safe, but two in particular are less so. During the eradication campaign, most smallpox vaccines (vaccinia virus) had a level of side effects which made them unacceptable for current use. Safer preparations have since been made by the deletion of specific DNA sequences. Type 3 poliovirus in OPV can revert to virulence, and poliomyelitis occurs at the rate of about 3 X 106 doses of...

Future Perspectives

The use of recombinant DNA technology can be expected to lead to the production of safer, more effective vaccines, as they can be more readily tailor-made to requirements and subsequently modified as required. Genetic engineering also offers the opportunity to construct multivalent vaccines in which the genes for several different antigens can be inserted into the same vector. In addition to the present recombinant vaccines available, which consist of the NDV HN or F gene sequences inserted...

Pathology and Histopathology

The most frequently and consistently observed microscopic lesions in fatal human Lassa fever are focal necrosis of the liver, adrenal glands and spleen. The liver damage is variable in the degree of hepatocytic necrosis. The liver demonstrates cellular injury, necrosis, and regeneration, with any or all present at death. A substantial macrophage response occurs, with little if any lymphocytic inflammatory response. Nevertheless, fatal cases do not exhibit sufficient hepatic damage to implicate...

Genital Cancer

Clinical studies, and especially data from molecular biology, suggest that certain types of human papillomavirus (HPV) are of etiological importance for genital cancer. In developing countries, carcinoma of the cervix uteri is the most frequent type of female cancer. HPV DNA can be found in 80-90 of the tumors, and the early genes E6 and E7 are usually expressed. The most prevalent type in epidermoid carcinomas is HPV 16. HPV 18 may be preferentially associated with adenocarcinomas. Other types...

Papillomaviruses HPV

Infections with HPV types are ubiquitous, with over 80 types that cause a variety of wart-associated conditions. While most lesions are benign, some, especially those caused by HPV-16, -18 and other oncogenic HPV types, may progress to premalignant and malignant lesions. Papillomaviruses are causally associated with cervical cancer, which is diagnosed in 15 000 American women annually and causes approximately 4500 deaths. Types 6 and 11 are responsible for common genital infections and also for...

Prevention and Control of Cardiovirus Infections

Given that the introduction of cardioviruses to domestic swine, zoo populations or captive primate colonies can constitute a considerable veterinary and economic problem, it would be desirable to have efficacious cardiovirus vaccines available to prevent epidemics. In 1989, Duke and Palmenberg prepared several Mengo cDNAs in order to determine the nucleotide sequence of the genome. Their enzymatic procedures accidentally truncated the poly(C) tracts in the 5' UTRs of several cDNAs (e.g. C UCxo...

Herpesviruses

The herpes viruses, Cytomegalovirus, Epstein Barr virus, herpes simplex and varicella zoster represent the greatest potential threat to transplant recipients. All four are present in the latent state in a high proportion of individuals, and all four can cause serious or fatal disease in the immunocompromised host. Background In a normal individual, defense against CMV is mediated by specific cytotoxic T lymphocytes, by production of specific antibody and perhaps also by MHC unrestricted...

Host Range and Virus Propagation

Rabies virus infects a very broad array of animal species, perhaps the widest range of any animal virus. Commonly infected are dogs, wolves, foxes, jackals, skunks, raccoons, raccoon dogs, vampire bats, insectivorous bats and mongooses the animals bitten by these species develop sporadic cases of rabies (these include cats, cows, horses, badgers and woodchucks) although the virus in those species rarely becomes enzootic. Humans are mostly infected after bites by rabid dogs. Propagation is...

Hepatitis Viruses

Hepatitis, or inflammation of the liver, can be caused by many different viruses and chemical substances. Viruses may cause acute infection (hepatitis A virus) or acute infection with the possibility for chronic liver infection leading to cirrhosis and hepatocellular carcinoma. Two major causative agents of acute and chronic disease are hepatitis B (HBV) and hepatitis C (HCV) viruses. The World Health Organization estimates the worldwide population of HBV carriers at about 350 million, with 75...

Industries Affected by Phage Infection

Reliable data on the severity of phage infection of industrial fermentations are difficult to obtain. This is primarily because release of this information raises confidentiality concerns of private industry. Therefore, inference must be made from publications citing incidences (although not degrees) of phage infection or reporting developments to cope with phage problems. Such information suggests that phage problems are pervasive, although assignment of an accurate monetary value on lost or...

DNV Disease and Ecology

There have been a number of reports of DNV diseases of economically important insects in Japan and the Peoples' Republic of China. A disease of the silkworm B. mori in the vicinity of Ina City, Japan, in 1968 has led to the discovery of B wDNV. At least two other isolates of DNV from diseased silkworms were later discovered in Japan and in China. Epizootic spread of DNV was observed in Japan in silkworm sericulture farms and in mulberry pyralids in mulberry plantations. The virus isolated from...

Transmission

Cats persistently infected with FeLV shed virus in their saliva, urine and feces but, as the virus is fragile, close contact is required for transmission. The most frequent routes involve saliva and transplacental spread. Kittens infected in utero become persistently infected, but the consequences of infection in older cats depend on a number of factors. There is an age-related resistance to infection such that cats up to 12 weeks of age are highly susceptible but above 16 weeks they are...

Prevention and Control of Pseudorabies

The strategy selected to control PR has depended on (1) the type of operation carried out by the producer (farrow-to-finish, seedstock, feeder pig producer, feeder pig finisher) (2) financial considerations (3) availability of suitable replacements (4) the disease profile of the herd and (5) PRV status in the area. Slaughter of an entire herd and repopulation is considered with single isolated outbreaks in non-infected districts, but may also be necessary when disease is detected in seed stock...

DNA Viruses

Comprising a subfamily of the Parvoviridae, the Densovirinae contains members (DNVs) that are invertebrate-specific viruses, and that have a single-stranded linear DNA genome. Densonucleosis viruses (DNVs) have been shown to cause lethal infections in hosts from the orders Lepidoptera, Diptera and Orthoptera (locusts and crickets). The virions are relatively stable in the environment, but are apparently highly susceptible to ultraviolet (UV) light. Horizontal transmission is either via...

Properties of the Genome

All members of the Hepadnaviridae family have a partially double-stranded DNA genome of about 3 kb that is held in a circular conformation by a short cohesive overlap between the 5' ends of the two DNA strands (Fig. 1). One strand is always complete in virus particles, whereas the second strand is incomplete, with a 3' end that is heterogeneous in location. The incomplete strand is of plus polarity and the complete strand of negative polarity. When these viruses infect a cell, the plus strand...

Genetics

MMTV causes mammary adenocarcinomas by infection of the mammary epithelium with either exogenous or endogenous virus. The genetic factors that influence mammary tumor incidence in mice include B and T cells are infected in small intestine Virally-encodod superamigen expands infected B and T cells B and T cells are infected in small intestine Virally-encodod superamigen expands infected B and T cells (1) the presence or absence of milk-borne virus, (2) the presence of an infectious endogenous...

Perpetuation of Viruses in Nature

Perpetuation of a virus in nature depends on the maintenance of serial infections, i.e. a chain of transmission the occurrence of disease is neither required nor necessarily advantageous. Influence of the clinical status of the host Infection without recognizable disease is called subclinical or clinically inapparent. Overall, subclinical infections are much more common than those that result in disease. Their relative frequency accounts for the difficulty of tracing chains of transmission,...

Viruses of Euryarchaeota Halophages

All of the halophages isolated to date are head and tail phages similar to various coliphages (e.g. T phages and A relatives). Halophages have isometric, icosa-hedral heads of widely differing sizes and tails, which in the case of OH, Hsl, HF1, HF2 and OChl are contractile. In the phages OH and ON tail fibers have been described, in the phages Hh3 and OChl collars. The DNA of halophages is double-stranded and varies between 30 and 60 kb in size, with the exception of Jal which carries an...

Ocular Disease Caused by DNA Viruses

DNA viruses (Table 2) are responsible for most significant ocular viral infections in the industrialized world. Even the protean ocular manifestations of the HIV, an RNA virus, result largely from reduced immunity to DNA viruses. Adenovirus is probably the most common DNA virus to cause eye disease. Three common ocular syndromes have been identified. Simple follicular conjunctivitis occurs with infection by many adenovirus types and may be subclinical. Pharyngoconjunc-tival fever typically...

Info

Figure 3 Heliothis armigera (cotton bollworm) cadaver after infection by HaNPV. Figure 3 Heliothis armigera (cotton bollworm) cadaver after infection by HaNPV. suited of the insect viruses for development as commercial pest control agents. Past and current uses of baculoviruses Baculo-viruses have been used for many years as pest control agents, being exploited both commercially (Table 2) and noncommercially. Early reports of use include the Chinese army using mortars to fire infected larvae...

Epidemiology

There have been at least three panzootics. The first began in 1926 and spread to most countries before it eventually subsided in the late 1950s as the result of widespread vaccination. The second panzootic emerged in the late 1960s in the Middle East and spread rapidly to all continents and most countries by 1973. The third panzootic appears to have emerged in the late 1970s in the Middle East and is thought to have been spread across Europe and then to many other countries by racing pigeons,...

Virion Proteins and RNA Segments

The spherical Bunyaviridae virion consists of four structural proteins two internal proteins (N and L) and two (perhaps three in some nairoviruses) external glycoproteins which are inserted in the viral membrane (Fig. 1). By convention, the glycoprotein of greater molecular weight (or slower electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gels) is termed Gl. There is no equivalent of a matrix protein to stabilize the virion structure. The three genomic RNA segments, which are...

Viruses Affecting the Heart

Viruses may affect the heart in a number of different ways. Developmental defects may occur as a result of intrauterine infection by such viruses as rubella, and infection of the myocardium may be induced by a large number of viruses in different groups, although infection by enteroviruses probably represents the commonest cause of acute and chronic heart muscle disease. As yet, there is little evidence to support the role of viruses as a cause of endocardial disease. Although the myocardium is...

Geographic Distribution

Peste Des Petits Ruminants Distribution

Rinderpest is enzootic on the Indian subcontinent and in parts of the Middle East and Eastern Africa. Sporadic outbreaks occur in countries bordering the enzootic regions. Peste des petits ruminants is enzootic in parts of West Africa but in the past few years it has spread across a broad belt of sub-Saharan Africa and eastwards through the Middle East and to southern Asia as far as Bangladesh (Fig. 1). It was thought until recently that India was free from peste des petits ruminants virus and...

Dhfr

A From inserted ORSV coat protein promoter. a From inserted ORSV coat protein promoter. The viral coat protein gene can, in some instances, be manipulated in order to express foreign sequences, though it always leads to lower fitness in terms of systemic spread. Although for some viruses the coat protein is dispensable for cell-to-cell movement (e.g. TMV), this structural protein cannot be omitted for long-distance transport of the inoculated vector (via the vascular system) throughout the...

Prevention and Control

The control of domestic Ae. aegypti mosquitoes is an important measure, but has proven difficult to sustain. The most effective approach to prevention is immunization of the human population in endemic areas. Yellow fever 17D is a live, attenuated vaccine produced in embryonated eggs. Over 300 million people have been immunized with this inexpensive product, which has proven safe and highly effective. Recent efforts have focused on the production of a new vaccine derived from a full-length cDNA...

Peach latent mosaic viroid

Figure 1 Secondary structures of potato spindle tuber and peach latent mosaic viroids. (A) A rod-like secondary structure for PSTVd is supported by a variety of physical studies as well as chemical and enzymatic mapping data. Boundaries of the terminal-left (Tl), pathogenicity, central conserved, variable and terminal-right (TR) domains are indicated by vertical lines. (B) Proposed lowest-free-energy structure of PLMVd. Predicted self-cleavage sites in the plus and minus strands are indicated...

Viruses that Promote Apoptosis DNA viruses

Adenoviridae Adenoviruses encode proteins that promote apoptosis at later stages in the productive cycle. These are encoded in the E3 and E4 regions. The E3 11.6K, Ad death protein (ADP) is expressed at high levels late in infection and may bring on apoptosis, but this has not been demonstrated. It is required at very late stages for efficient cell lysis and virus release. African swine fever virus Monocytes, macrophages and mononuclear cells infected with AFSV undergo apoptosis. This gives...

Properties of the Virion

The morphology of the varicella-zoster virus (VZV) virion is similar to that of other herpesviruses. The virion is 180-200 nm in diameter and is made up of four structurally distinct elements. The linear duplex viral DNA genome is packaged in a central 75 nm core, contained within an icosahedral nucleocapsid 100 nm in diameter, with 5 3 2 axial symmetry. The nucleocapsid is composed of 162 hexameric and pentameric capsomeres with central hollows wider on the outside than the inside. A...

Enterovirus type 70 EV70 History

EV70 is the second human enterovirus isolated from extensive epidemics where the dominant clinical manifestations are in the eye, the first being coxsackievirus A24 variant CA24v . Together these viruses are universally recognized as causative agents of acute hemorrhagic conjunctivitis AHC . EV70 was first isolated in 1971 during the 1969-1971 wave of AHC in Morocco, Singapore, Hong Kong concurrently with CA24v and Japan. Explosive outbreaks of acute conjunctivitis, thought intitially to be due...

Pyrogenic Exotoxins of Streptococcus Pyogenes and Staphylococcus Aureus

The streptococcal pyrogenic exotoxins also known as erythrogenic toxins or scarlatinal toxins are produced by S. pyogenes and cause the rash of scarlet fever. The enterotoxins of S. aureus cause the symptoms of staphylococcal food poisoning, and toxic shock syndrome toxin of S. aureus is responsible for many manifestations of toxic shock syndrome. These toxins share antigenic properties, amino acid sequences, and biological activities including pyro-genicity, enhancement of sensitivity to...

Virus Capsid Threedimensional Structure

Fmd Virus Structure

X-ray crystallographic analysis of the Mengo virion at 0.3 nm resolution was reported in 1987 by Luo et al. The overall architecture of the capsid follows T 1 icosahedral symmetry, with one asymmetric unit comprising one molecule each of VP1, VP2 and VP3. The 60 VP4 molecules occupy internal positions, extending from under the threefold axes to form part of an annular structure under the fivefold axes there Table 1 Physicochemical properties of the cardiovirion Table 1 Physicochemical...

The Reovirus Particle

Reovirus particles consist of a core some 55 nm in diameter which is surrounded by an outer capsid shell that is about 12.5 nm thick Fig. 1 . Since the thickness of the core shell is about 7.5 nm, the central cavity accounts for about 12.5 of the reovirus particle volume, and the core for about 33 . Both the outer capsid and the core shell are composed of capsomers which are arranged with icosa-hedral symmetry. The reovirus particle surface reveals 600 protrusions, presumably capsomers,...

Dfk

Ccmv Virus Symmetry

Nudaurella co capensls virus Ncov - r 4 cowpea chlorotic mottle virus CCMV - 7 3 southern bean mosaic virus SBMV - 7 3 Figure 2 Structure of A vertebrate, B insect and C plant virus protein subunits that assemble into icosahedral shells. The name of the virus appears below the corresponding protein subunit along with the capsid triangulation number T explained in Fig. 3 . The N- and C-termini are labeled with the residue numbers in brackets. Many virus subunit structures determined to near...

History and General Characteristics

Isolation and characterization of bee viruses began in the 1960s, with work on two diseases, sacbrood and paralysis, which have striking symptoms. Sacbrood, although extremely common in Britain, was, until the virus was isolated, dismissed there as a genetic disorder. Similarly, paralysis was ascribed to independent, but accompanying and very common, well-known parasites, especially microsporidia and mites, which do not cause any overt symptoms. Many, if not all, of the viruses of bees persist...

Viruses Occurring in Europe

Tahyna TAH virus is widely distributed in Europe, and has been reported in Africa. TAH virus produces an influenza-like febrile disease, with occasional central nervous system involvement. The virus is a bunyavirus of the California serogroup, in the Bunyaviridae. Like La Crosse virus, small forest mammals are TAH virus reservoirs, and the virus is horizontally and transovarially transmitted by Aedes mosquitoes. There are no effective control measures. Omsk hemorrhagic fever occurs in a...

Viruses Occurring in Australia

Murray Valley encephalitis MVE occurs primarily in southeastern Australia, with cases appearing occasionally in other parts of the country and in Papua New Guinea. Febrile disease leads to encephalitis and, in severe cases, death. Neurologic sequelae are common in survivors. Children are predominantly affected. Large water birds are the main vertebrate amplifying hosts, but mammals are also reservoirs. The virus is transmitted mainly by Culex annuliros-tris mosquitoes. It is maintained in...