Dengue fever

Tropical Viral infection (TVI) and Hemorrhage fever

Viral hemorrhagic fevers are a group of distinct acute viral infections which cause various degrees of hemorrhage, shock and sometimes death.

Many are rarely identified and most are geographically very restricted

This section deals with the major VHF’s:

- Yellow fever

- Dengue fever

- Lassa fever

- Hanta virus

Common features:

- non- hemorrhage disease is common and death from blood loss is rare

- Most viruses have a zoonotic reservoir (E.g. Lassa fever, rat)

- Many have an insect vector (E.g. Congo Crimean hemorrhage fever; ticks)

- Most infections occur in remote areas leading to under reporting

- Some (Lassa, Abola, Congocrimean) can be transmitted from person to person. Then morbidity and mortality tend to be greater.

- Lassa fever is the main viral hemorrhage fever with potential.

- Ebola had not been reported since 1976 but in 1995 caused outbreaks in Zaire.

- Reports of Marburg are very frequent

- Congocrimean fever is endemic in Middle East and Eastern Europe risk of transmission is much lower.

Lassa Fever:

Epidemiology: its endemic in West Africa, Sierra Leona, Liberia and Siberia are the main endemic foci up to 50% of indigenous population have serologic evidence of past infections.

Result in 300, 000 cases and 5000 deaths annually.

Is spread mainly by contact with aerosolized urine from chronically infected multimammate rota.

Must be suspected in any febrile patient recently refused from endemic area.

Incubation period: 18 days being shorter for secondary cases.

Pathology and pathogenesis:

Single stranded arena virus with a genome coding for viral polymerase and several structural proteins with the development of immunity, Ab against surface glycoproteins develop, but those aren’t very effective at neutralizing the virus.

Following acquisition a viremia develops with, in severe cases, the development of a leaky capillary syndrome.

Clinical features:

Typically:

• Gradual onset of influenza – like symptoms
• Exudative pharyngitis
• Conjunctivitis
• Proteinurea

Complications:

• Shock and leaky capillary
• Encephalopathy
• Pericarditis and congestive cardiac failure.
• Senso- neural deafness.

Yellow Fever

It is due to a Flavi virus and is mosquito borne.

Recent epidemics in Nigeria have caused more than 150, 000 cases and 30,000 deaths.

It has the following characteristics.

• It is a zoonosis of monkeys endendemic in Africa and south America.
• It may cause epidemics in two forms “ jungle” and “Urban”
• Incubation period: 3-6 days

Pathology and pathogenesis:

Following inoculation, the virus replicates in drainage lymph nodes and then causes viremia. A characteristic mild zonal hepatic necrosis occur. Kidneys show evidence of acute tubular necrosis.

Clinical features:

Illness ranges from mild to catastrophic. Typically there is:

• An acute biphasic fever with abrupt onset of severe influenza-like illness, conjunctivitis and relative bradycardia.
• After remission for a few days, toxicity returns with severe vomiting abdominal pain, jaundice, renal failure, hypotension and hemorrhage.

Complications:

• Shock
• Coma
• Convulsions
• Myocarditis
• Hepatitis

Dengue fever

Epidemiology: most important of the Arbovirus C 40-80million people becoming infected worldwide each year.

- it is endemic through out the tropics

- it is transmitted by A. Acgypti

- It is present as four serotypes each of which can infect humans.

- In a country where multiple serotype circulate, the first 2 infections may cause illness, but the 3^rd and 4^th tend to be asymptomatic.

In children (and less common in adults), the second infection may cause hemorrhage Dengue shock syndrome.

- Incubation period: 3 – 8 days.

Hemorrhage fever with renal syndrome:

Epidemiology: Hanta viruses are rodent viruses that cause a range of illnesses in humans.

• A family of Hanta viruses exist, the members of which are associated with different clinical syndromes.
• Hantaan viruses is the agent of hemorrhage fever and renal syndrome (HFRS) which is distributed in Russia, the far East and Asia (reservoir; the field mouse)
• Puumula virus is the cause of nephropathia epidemica (a milder variant, distributed in Europe, esp. Scandinavia. (reservoir; the role)

And a new strand has been identified as the cause of pulmonary syndrome (Pulmonary syndrome Hanta virus)

• The incidence of HFRS is about 4/100,000 population in Russia.
• Rodents excrete the virus asymptomatically. Human infection occurs via contamination of abrasions or mucous contamination by excretion, by inhalations of aerosols of dried saliva or excreta or by rodent bites.
• Most hanta virus infections are subclinical seroprevalence surveys show 10% of persons.
• Incubation period: 2 -3 weeks

Pathology and pathogenesis:

Hanta virus belongs to Bunya virus family, SS RNA viruses. The acute renal disease is pathologically typically of an acute interstitial nephritis.

Clinical symptoms:

• Range from mild illness with minimal renal dysfunction; to 1 with severe renal failure, shock, pulmonary edema and CNS involvement

HFRS (hem. Fever Renal Syndrome) is divided into 5 clinical stages:

1- febrile

2- hypotensive (5^th day)

3- oligourea (day 9)

4- polyuric

5- convalescent (by day 14)

Most patients present with:

· Abrupt onset of influenza like symptoms.

· Blurred vision, conjunctivitis

· Flushed face, periorbital edema

· Erythematous rash

· Palatal and axillary petechia

Complications:

• hypotensive shock
• hemorrhage
• renal failure
• non cardiogenic pulmonary edema
• encephalopathy

Дата добавления: 2015-10-29