Yes, this is a masked palm civetSelected Diseases - Part 2
I Virus Infections of Upper Respiratory System
1) Rhinovirus 2) Coronavirus
3) Adenovirus
II Virus Infections of the Lungs
1) Respiratory Syncytial Virus 2) Hantavirus
3) Influenza
III Scary Emerging Viruses
1) Lassa Fever 2) Ebola and Marburg
3) West Nile virus
I Virus Infections of Upper Respiratory System
The Common Cold is uncomfortable. But don’t expect any sympathy. You just suffer, preferably in silence and alone. Standard professional advice is that without treatment it will last about 7 days and with treatment, about a week.
Colds are spread by both airborne transmission and contaminated objects. Experiments exist that support and contradict each. Probably some of each method is involved.
Causative agents = a whole horde of viruses. There are at least 200 viruses that can cause colds. Not a serious problem unless the infection spreads to the sinuses, middle ear or lower respiratory tract, where it may be more serious. Most common are rhinoviruses, next coronaviruses and then adenoviruses.
1) Rhinovirus (Talaro pages 778-781)
Linear Single-Stranded RNA
Small spherical virus, (no extra outer envelope)
Over one hundred different Rhinoviruses (makes vaccination useless)
About 50% of colds
Very infectious - 95% of people exposed to a rhinovirus strain they have not had before are infected, and 75% of those infected become ill
Decongestants and antihistamines do NOT cure colds. They only relieve the symptoms
Twelfth century Egyptian physicians recommended chicken soup (reportedly learned from the ancient Greeks)
Belong to the picornavirus family (includes polio)
Cannot replicate at full body temperature so it stays in the upper respiratory tract where temperature is a couple of degrees lower
Destroyed by stomach acid so it doesn’t reach your intestines like polio
Virus attaches to cell surface receptor ICAM-1 (Intercellular Adhesion Molecule-1)
ICAM-1 sticks out from human cells and binds into a pocket in the virus surface
Zinc nasal sprays and lozenges shorten the length of a cold from 10-14 days to 4-7 days. Zinc binds in the pocket where ICAM-1 normally binds and blocks the receptor
2) Coronavirus (Talaro pages 772)
Single stranded RNA
Spherical virus with extra outer envelope and prominent spikes
SARS = Severe acute respiratory syndrome
SARS is due to an unusually virulent coronavirus &emdash; sometimes complicated by joint infections with other viruses. Unlike other coronaviruses SARS virus may get into the lungs.
Where did the SARS virus come from?
Coronaviruses with 99% sequence similarity to human SARS have been isolated in Guangdong, China, from healthy masked palm civets (Paguma larvata), a cat-like mammal closely related to the mongoose. The palm civet is eaten as a delicacy in Guangdong. Humans probably became infected as they raised and slaughtered the animals rather than by eating infected meat.
Yes, this is a masked palm civet
3) Adenovirus (Talaro pages 744-745)
Small spherical virus (no extra outer envelope)
Double stranded DNA
About 30 different types infect humans
Prefer the respiratory tract or intestine
Aggregations of virus particles (plus incomplete particles) form in nucleus of infected cells which then usually burst
II Virus Infections of the Lungs
Lung infections are usually due to bacteria or to influenza virus. But some other viruses are also capable of causing lung infections e.g. SARS (an unusual coronavirus &emdash; see above), RSV or Hantavirus.
1) Respiratory Syncytial Virus (RSV) (Talaro pages 759-760)
Causes viral bronchitis and pneumonia. Also known as Pneumovirus. Particularly important in infants where it is relatively serious. A cause of concern in hospital nurseries where it can spread from infant to infant by direct contact and by inhalation of airborne particles and may cause fatalities. In older children and adults it usually just causes a common cold.
The antiviral drug, ribavirin (= virazole), can be administered as an aerosol and can diminish the severity of the symptoms.
Paramyxovirus family
2) Hantavirus (Talaro page 756)
In 1993 there were several cases of a severe respiratory infection, most of them fatal, in the Four Corners region of New Mexico. The lungs filled with fluid from the capillaries and the patients literally drowned in the fluid. Called Hantavirus pulmonary syndrome (HPS) &emdash; about 30% fatality. Virus is the Sin Nombre hantavirus. Since then the disease has occurred sporadically.
The virus was unknown before in the US but is closely related to the virus causing Korean Hemorrhagic Fever and identified in 1976. It was named Hantavirus, after the Hantaan River in Korea. The fatality rate of the Korean virus is around 5%.
Hantavirus is carried by rodents and is now known to be found all around the US. The main vector of the Sin Nombre Virus is the white-footed deer mouse, Peromyscus maniculatus. Virus is excreted in rodent urine and feces and breathed in on dust after drying. Most serious infections have been in the Four Corners area - where New Mexico, Arizona, Colorado and Utah meet. So far no human-human transmission has been seen. The disease is more prevalent after rainy years, which lead to a good pinion harvest and an explosion of the mouse population (they eat the pinions, a type of nut).
Hantavirus belongs to the Bunyavirus family. Single-stranded RNA viruses with an inner protein shell surrounded by an outer envelope. Like flu the genome is divided into several segments of RNA.
3) Influenza (Talaro pages 751-756)
Caused by influenza virus and is highly contagious. Since flu infects the lungs, as well as the upper respiratory tract it could be regarded as a type of pneumonia also. The unusually virulent flu epidemic ("Spanish flu") of 1918 to 1920 killed millions of people &emdash; more than the number who died in World War I.
Virus is in the orthomyxovirus family. It contains single stranded RNA inside an inner protein shell surrounded by an outer envelope. The genome is unusual in being divided into 8 segments. This allows rapid shuffling of genes between different virus strains. In addition the virus mutates rapidly.
The result is constant genetic change. Every few years a new strain of influenza goes around. The antigens (surface proteins) change from strain to strain and so new vaccines are needed for each new epidemic. Although the vaccines are effective they are not long lasting.
Virulence factors - both are protein spikes located on the surface of the virus and vary slightly from strain to strain. Flu viruses are designated by H and N numbers (e.g. H5N1, H3N2 etc). These refer to:
Hemagglutinin, for attachment to cells of the respiratory mucous membranes. Also binds to red blood cells and causes them to clump &emdash; hence the name.
Neuraminidase is needed for assembly of virus particle. It hydrolyzes the sialic acid on host cell membranes.
There are strains of influenza viruses that infect domesticated and wild animals as well as humans--swine, horses, birds, especially ducks and chickens. Every so often these hybridize.
Influenza alone does not have a high fatality rate. But it does predispose to bacterial infections that may be fatal (especially in the old or sick). Because influenza is highly contagious a lot of people get it when it goes around. So even though the fatality rate is low, there will be a significant number of deaths. Antibiotics can help with the secondary bacterial infections but not the influenza virus itself. Most at risk are the elderly and very young.
Influenza virus may be treated with amantadine or sometimes ribavirin. This is not practical on a widespread basis.
Ribavirin (Virazole) is also used to treat Lassa fever, respiratory syncytial disease and Hanta virus. It interferes with the synthesis of viral mRNA by inhibiting DNA-dependent RNA polymerase, inosine monophosphate dehydrogenase and various viral GTP-dependent enzymes. It has the broadest spectrum of activity of any of the anti-viral compounds.
Amantadine is only used to treat influenza A. It interferes with uncoating of the virus when it enters the cell. The virus must "uncoat" to release its RNA before it can take over the cell and replicate. Amantidine binds to M2 protein if the virus particle and stops this. Rimantadine is a related drug that works by the same mechanism.
III Scary Emerging Viruses
For Hantavirus and SARS see above.
1) Lassa fever (Talaro page 756)
Discovered in Africa in 1969. Named after a town in Nigeria. Spread like Hantavirus by rodents. Some strains of this virus are incredibly virulent others relatively mild.
Lassa fever belongs to the Arenavirus family. Like the Bunyaviruses (such as hantavirus) these are single-stranded RNA viruses with an inner protein shell surrounded by an outer envelope. The genome is divided into two segments of RNA which can be reshuffled between related viruses.
Lassa Fever is an endemic disease of Central and West Africa. It occurs year round with peaks from January to April when fields are burned, and the mice flee to the houses.
Rodent to human transmission occurs via:
Human to human transmission occurs via:
2) Ebola and Marburg viruses (Talaro page 753)
These are Filoviruses - thin filamentous single-stranded RNA viruses with an inner protein shell surrounded by an outer envelope. They are the largest viruses in the sense of physical size (length) although they only have a few genes (about 7).
1967: Marburg near Frankfurt, Germany. Outbreak of an unknown disease in a laboratory. Source was ell cultures from African green monkeys. Highly infectious: 31 cases, 7 deaths.
1976: Outbreak of a previously unknown hemorrhagic fever in Zaire & Sudan 'Ebola disease': 500 diagnosed cases, 460 deaths!
The true animal reservoir is uncertain but bats are the number one suspect. They are infected but often do not become ill.
Sometimes caught from eating bushmeat (particularly primates).
Serological surveys in Africa suggest that asymptomatic human infections occur sporadically.
Hemorrhagic fevers: massive loss of blood and fluid into the tissues and bleeding from bodily orifices. Ebola is especially nasty: brain fills with blood clots, liver turns yellow and cracks, skin liquefies, stomach breaks down, constant bleeding. 50% to 90% fatal.
3) West Nile virus (Talaro page 766)
West Nile virus appeared in the USA in 1999 and has since spread all over the country. Natural host is birds, especially birds of the crow family. The virus is carried between birds by mosquitoes. It is not known how West Nile virus reached North America. It could have arrived in a migratory bird or in an infected person (or mosquito) that traveled to the New York area in an airliner.
CDC Data for the United States:
| Years | Cases | Fatalities |
| 1999-2001 | 149 | 18 |
| 2002 | 4156 | 284 |
| 2003 | 9862 | 264 |
West Nile virus belongs to the Flavivirus family that includes yellow fever and dengue fever. These are spherical single-stranded RNA viruses with an inner protein shell surrounded by an outer envelope. They are all carried by mosquitoes.
Most people who are infected show no symptoms or very mild ones. Occasional people suffer severe disease (especially in those with weak immune systems).
Mild cases: flu-like symptoms such as fever and headache
Serious cases: headache, high fever, nausea, vomiting, difficulty swallowing, drowsiness, muscle weakness and paralysis and fatal problems such as meningitis and encephalitis.
History of West Nile virus
1937 - discovered in a woman in the West Nile district of Uganda
1990s - outbreaks in Romania, Algeria, Russia, Czech Republic, Africa, Israel
1999 &emdash; New York
Control
There is no treatment and no vaccine.
Primary means of controlling the disease is by reducing the number of times people are bitten by mosquitoes.
a) Mosquito control
Eliminate pools of stagnant water (for example, in old tires, clogged house gutters, and unattended bird baths)
Managing bodies of water to increase the numbers of mosquito predators
Treating mosquito-breeding areas with chemical agents (e.g. methoprene) or biocontrol agents (e.g. the bacterium Bacillus thuringiensis) to kill mosquito larvae
Spraying adult mosquitoes with chemical insecticides, such as resmethrin from trucks or helicopters
b) Personal Protection
Wear long sleeves and long pants
Avoid being outdoors when mosquitoes are most active (the evening)
Avoid areas where mosquitoes are common (such as swamps)