Viral Diseases - DENGUE

Dengue or dengue-like epidemics were reported throughout the nineteenth and early twentieth centuries in the Americas, southern Europe, North Africa, the eastern Mediterranean, Asia and Australia, and on various islands in the Indian Ocean, the south and central Pacific and the Caribbean. DF and DHF have steadily increased in both incidence and distribution over the past 40 years.  Annually, it is estimated that there are 20 million cases of dengue infection, resulting in around 24 000 deaths.

GENERAL: In most man is an accidental host infected when arthropods feed on him. Therefore quarantine of wild caught animals and elimination of ectoparasites should prevent:

(1.) TICK BORNE viruses:
        (a)  Russian-Spring-Summer Encephalitis;
        (b)  Louping Ill;

(2.) MOSQUITO BORNE viruses:
        (a)  DENGUE (Breakbone Fever, Dengue Hemorrhagic Fever)
              AGENT: Flavivirus, Flavidviridae
              RESERVOIR: nonhuman primates, occurs in Asia, Africa, Australia, the Caribbean including Puerto Rico, the Pacific Islands, S. Europe, S. America
              TRANSMISSION: mosquito vector (Aedes)
              DISEASE IN NONHUMAN PRIMATES: subclinical
              DISEASE IN HUMANS: The first phase of illness is usually mild fever, headache, myalgia, lymphadenitis, pharyngitis, rhinitis and cough lasting 1-5 days and is followed by 1-2 days of remission. The second peak of fever is accompanied by a morbilliform maculopapular rash. Severe hemorrhagic manifestations occur during the second phase especially in children.
             DIAGNOSIS: HI, CF, ELISA, or virus isolation.
             TREATMENT: Treat shock by expanding circulating blood volume. Acetaminophen given for discomfort. Prolonged convalescence.
             PREVENTION/CONTROL: Mosquito control by screening and insect repellents. Others, in addition to spread by vector, have presented problems in the laboratory as a result of contact with tissues or secretions of lab animals experimentally infected with virus. 

        (b) EQUINE ENCEPHALITIDES (EASTERN, WESTERN, AND VENEZUELAN). These are diseases of horses, mules, birds, humans, and other animals caused by the neurotropic viruses, Alphavirus and Flavivirus. Wild birds serve as a reservoir, and the virus requires an arthropod vector to transfer from reservoir host to other susceptible species. Mosquitoes, chicken mites and lice, ticks, and any other bloodsucking insects can serve as vectors. This group of encephalitis viruses is unique to the New World. Prevention is accomplished by adequate vector control and vaccination of horses. Pigeons, chickens, pheasants, prairie chickens, ducks, and geese are susceptible and, if infected when suitable vectors are present, may pose a potential source of disease for humans. There is a high mortality in humans infected with these viruses.

        (c)  CRIMEAN CONGO HEMORRHAGIC FEVER. Nairovirus, Bunyaviridae family. Causes epidemics in Bulgaria, USSR, and sporadic cases in Iraq, Pakistan and East Africa. Associated with tick bites, primarily Hyalomma genus. Also nosocomial outbreaks among hospital personnel.

        (d)  OMSK HEMORRHAGIC FEVER (rodents)

        (e)  KYASANUR FOREST DISEASE (monkeys) Togaviridae occurs in bonnet macaques, languors, and rodents in India spread by ticks lab workers in the US affected while working with infected primates (no vector) NHP exhibit fever, vomiting, diarrhea, epistaxis, and death. In humans, there is a sudden onset of fever which may be biphasic, with headache, generalized pains, prostration, conjunctivitis, diarrhea, and vomiting. Vesicles occur on the soft palate. Hemorrhagic manifestations may follow. Case fatality rate is 2-50%. Diagnosed thru serology or viral isolation. Treatment is supportive. Convalescent plasma with a high neutralizing antibody titer has been reported to be useful. Prevention is thru tick control.

        (f)  CHIKUNGUNYA: Maintained by vervets and baboons in Southern Africa. Transmitted by biting flies and mosquitoes

        (g)  RIFT VALLEY FEVER (Enzootic Hepatitis)

AGENT:

Phlebovirus, Bunyaviridae

RESERVOIR AND INCIDENCE:

Endemic in Africa and Egypt. Affects nonhuman primates, and man. Cattle, bats, and sheep may be reservoir hosts.

TRANSMISSION:

Mosquito vector highly contagious among laboratory workers where transmission does not require vector.

DISEASE IN ANIMALS:

Rapid death after fever occurs in lambs. In cattle abortion and diarrhea occur. Liver lesions predominate histologically, with areas of necrosis. Widespread hemorrhages occur.

DISEASE IN MAN:

Fever (which may be biphasic) has a sudden onset, with severe headache, muscle and joint pains and photophobia. In a small proportion of cases there are hemorrhages, liver necrosis, encephalitis and retinitis.

DIAGNOSIS:

Serology and virus isolation.

PREVENTION/CONTROL:

Control mosquitoes. Precaution in handling necropsy specimens. Arbovirus where the natural cycle of transmission DOES involve man: