Chapter 16 Viral Infections of the Blood, Lymphatic, Gastrointestinal, and Nervous Systems

16.1 Viral Infections Can Affect the Blood and the Lymphatic System Infectious mononucleosis is a blood disease. It particularly affects B lymphocytes in the lymph nodes and spleen. It is spread by contact with saliva. It is caused by the Epstein-Barr virus (EBV). Many children are infected and show no symptoms. Adolescents or young adults who are infected may have sore throat, enlarged lymph nodes, and fever

Figure 16.02: The Monospot Slide Test for Infectious Mononucleosis. It is a latent virus. Diagnosis involves observation of elevated lymphocyte levels. Antibodies can be detected by the Monospot test. No vaccine or drugs for treatment are available. EBV is also associated with: Burkitt lymphoma. Hodgkin disease. Multiple sclerosis. Figure 16.02: The Monospot Slide Test for Infectious Mononucleosis.

Cytomegalovirus (CMV) disease can produce serious birth defects. CMV disease is common, producing infectious mononucleosis-like symptoms. The virus may pass into the fetus of a pregnant woman, causing mental impairment. In immunocompromised people, it can reactivate. This can accelerate the progression of HIV to AIDS and infecting many bodily tissues.

Figure 16.03: Some Methods for the Transmission of Hepatitis B. Several hepatitis viruses are bloodborne. Hepatitis B virus (HBV) is a global health problem. 1 million die/year Virions consist of: a nucleocapsid surrounded by a core antigen (HBcAg). an envelope containing a surface antigen (HBsAg). Transmission usually involves direct or indirect contact with a bodily fluid. Figure 16.03: Some Methods for the Transmission of Hepatitis B.

Hepatitis B is an important sexually transmitted disease During the 1-6 month incubation period, the virus infects the liver Primary symptoms are fever, fatigue, loss of appetite, nausea and vomiting and dark urine Jaundice occurs after primary symptoms. Recovery occurs 3-4 months after the onset of jaundice, after which an immunity is developed. Persistent infections, cirrhosis, or liver cancer occur rarely. Several vaccines and drugs for treatment are available.

Figure 16.04: Hepatitis C Infections. Hepatitis C virus (HCV) is transmitted by blood Few symptoms are associated with primary infection. Most cases develop a symptomless chronic infection cirrhosis is the primary cause of liver transplants in the US HCV damage is the primary reason for liver transplants in the United States. Damage is accelerated by alcoholism and drug use. No vaccine is available Figure 16.04: Hepatitis C Infections. Data from: CDC

16.2 Some Viral Diseases Cause Hemorrhagic Fevers Flavivirusises can cause a terrifying and severe illness. They are also called arboviruses because they are arthropodborne. Yellow fever was the first human disease associated with a virus by Walter Reed. It is passed from person to person via blood-sucking mosquitoes Zoonosis is found in monkeys and other jungle animals

Figure MM03: Yellow fever virus. Primary symptoms of yellow fever are: abrupt headache. Fever. muscle pain. Most patients recover after symptoms abate in 3-5 days. In some patients, the illness reappears as: nausea. uncontrollable hiccups. black vomit, jaundice delirium. hemorrhaging of the gums, mouth, and nose. 50% of patients enter a coma and die from internal hemorrhaging. Two vaccines are available, but no therapeutic drugs exist. Figure MM03: Yellow fever virus.

Figure 16.05: TEM of dengue fever viruses. Dengue fever occurs in four types. It is transmitted by two species of mosquitoes Early signs of dengue fever include: high fever and prostration. then sharp pains and sensations like bones are breaking, thus the name “breakbone fever” Figure 16.05: TEM of dengue fever viruses. © Chris Bjornberg/Photo Researchers, Inc.

A rash from skin hemorrhages appear, followed by: Complications are unusual, unless one of the 3 other types of dengue fever enters the body later It causes dengue hemorrhagic fever, the immune system allows the new infection to replicate A rash from skin hemorrhages appear, followed by: severe vomiting and shock. decreased blood pressure. Vaccines are in clinical trials

Figure 16.06: The Ebola virus. Members of the Filoviridae produce severe hemorrhagic lesions Ebola hemorrhagic fever (EHF) has occasional outbreaks in Africa, causing 50-90% mortality. It appears to be zoonotic, with fruit bats as a possible reservoir. Transmission can occur with contact with blood or secretions from an infected person or contaminated objects. It damages endothelial cells, causing massive internal bleeding and hemorrhaging. Figure 16.06: The Ebola virus. Courtesy of Cynthia Goldsmith/CDC

Figure 16.07: Transmission of Lassa Fever Virus. Members of the Arenaviridae are associated with chronic infections in rodents. Lassa fever is caused by a zoonotic virus carried by rodents. It is transmitted through aerosol or direct contact with rodent excreta or contaminated food. Infection leads to: Severe fever. Exhaustion. Patchy blood-filled hemorrhagic lesions of the throat. Figure 16.07: Transmission of Lassa Fever Virus.

Figure MM04: Hepatitis A virus. 16.3 Viral Infections of the Gastrointestinal Tract are Major Global Health Problems Hepatitis viruses A and E are transmitted by the gastrointestinal tract. Hepatitis A is an acute inflammatory liver disease. It is commonly transmitted by food or water contaminated by the feces of an infected individual. Transmission can also occur by raw shellfish. Hepatitis A virus (HAV) belongs to the Picornaviridae family. Figure MM04: Hepatitis A virus.

Figure 16.08: Hepatitis A Viruses. Enlargement of the liver and jaundice may follow initial symptoms of hepatitis A. High standards of personal and environmental hygiene are needed to prevent transmission. Three vaccines are available for different age groups. Hepatitis E is also spread by oral-fecal route with similar symptoms Figure 16.08: Hepatitis A Viruses. © James Cavallini/Photo Researchers, Inc.

Several unrelated viruses can cause viral gastroenteritis Viral gastroenteritis is a general name for illnesses involving: diarrhea nausea vomiting fever cramping headache Malaise Can be severe in infants, elderly and immunocompromised

Rotavirus infections can be a deadly infection in children. Transmission occurs through ingestion of contaminated food or water. The viruses invade the small intestine, inducing diarrhea. Treatment is oral rehydration therapy. Two vaccines are available. Figure 16.09: Rotaviruses. © Science Source/Photo Researchers, Inc.

Norovirus infections are a common cause of nonbacterial gastroenteritis in adults. Transmission occurs through: the fecal-oral route. direct person-to-person contact. contact with infected surfaces. Recent outbreaks have been seen on cruise ships. They are highly contagious. Dehydration is the most common complication.

Coxsackie virus causes hand, foot and mouth disease Contagious disease affecting infants and young children Symptoms include Fever Poor appetite Malaise Sore throat Rash on palms of hands and soles of feet

16.4 Viral Diseases of the Nervous System Can Be Deadly The rabies virus is of great medical importance worldwide. It has the highest mortality rate of any human disease once symptoms have begun. Figure 16.01: Rabies Distribution Worldwide. Reproduced from WHO, Essential rabies maps

Figure MM08: Rabies virus. Animal rabies occurs in warm-blooded animals. It enters the body through a skin wound contaminated with a bodily fluid from an infected animal. The incubation period varies from 6 days to 1 year. It depends on the location of entry and the amount of virus entering the body. Figure MM08: Rabies virus.

Figure 16.10: The Rabies Virus. Fever, headache, and increased muscle tension develop. Patients become alert and aggressive, followed by paralysis and brain degeneration. Death from respiratory paralysis occurs within days. Post-exposure immunization can be done immediately after a bite. Figure 16.10: The Rabies Virus. © Eye of Science/Photo Researchers, Inc.

Figure 16.11: Reported Cases of Animal Rabies. In animals: Furious rabies involves violent symptoms like: wide eyes. drooling. unprovoked attacks. Animals with dumb rabies are docile and lethargic. Wild animals are vaccinated with inoculated dog food and fish meal. Figure 16.11: Reported Cases of Animal Rabies. Source: Available at: http://www.cdc.gov/ncidod/dvrd/rabies/Epidemiology/Epidemiology.htm. Accessed July 2003.

The polio virus may be the next infectious disease eradicated. Polio (poliomyelitis) infects the gray matter of the spinal cord and brain. Polioviruses enter the body through contaminated food and water Polioviruses multiply in: tonsils. lymph tissue. gastrointestinal tract. Figure 16.12: Polio viruses. © Science VU/CDC/Visuals Unlimited

Figure MI16: Global Polio Cases. Sometimes the viruses pass through the bloodstream to the meninges. This can result in paralysis of limbs and trunk. In bulbar polio, the viruses infect the medulla, affecting nerves in the: neck. face. upper torso. Oral Trivalent vaccines contain all 3 types of poliovirus. Postpolio syndrome occurs in individuals who had the disease decades ago. Figure MI16: Global Polio Cases. Source: WHO; http://www.polioeradication.org/content/general/casemap.shtml

Figure 16.14: Global Distribution of Major Arboviral Encephalitis. Arboviruses can cause a type of primary encephalitis Arboviral Encephalitis is an acute inflammation of the brain. pain in the head and neck, convulsions, coma. Those who recover may have paralysis and mental disorders. Humans are dead-end hosts There are many forms, many transmitted by mosquitoes and ticks. Figure 16.14: Global Distribution of Major Arboviral Encephalitis. Data from: CDC

Figure 16.13: Transmission of Arboviral Encephalitis. West Nile virus disease is an emerging disease in the Western hemisphere. It can infect birds, mosquitoes, humans, and some other mammals. Humans generally contract it through mosquito bites. Figure 16.13: Transmission of Arboviral Encephalitis.

Many infected people remain asymptomatic, or are ill for a few days. Rarely, the patient will develop encephalitis or meningitis . This can result in permanent neurologic effects or death. There is no vaccine or specific treatment for West Nile fever. Figure 16.16: Incidence of West Nile Virus. Figure 16.15: West Nile Virus. Courtesy of Cynthia Goldsmith/CDC Reproduced from: Morbidity and Mortality Weekly Report, 59(53);1-116