Rift Valley Fever

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Rift Valley Fever (RVF) is a viral disease that affects mainly animals and occasionally humans. The virus is a member of the Phlebovirus genus, one of the five genera in the family Bunyaviridae. The  disease is frequently reported following heavy rainfall and floods.  RVF is mainly transmitted from  animals (sheep, cattle, goats, camels) to humans through close contact with infected animals (such as handling meat and body fluids and consumption of raw milk). During established RVF outbreaks  in  animals,  humans  can  also  get  infected  through  bites  of  infected  mosquitoes  and  other  biting  insects.

The incubation period of RVF varies from 2 to 6 days. These symptoms usually last from 4 to 7  days.  Most  of  the  infected  people  recover  on  their  own.  However,  a  small  proportion  gets  complications such as vomiting blood, nose bleeding and passing bloody stool. Rift Valley fever is  difficult  to  distinguish  from  other  viral  haemorrhagic  fevers  as  well  as  many  other  diseases  that  cause fever, including malaria, shigellosis, typhoid fever, and yellow fever.

Case Definitions 

Suspected  case:  Early  Disease:  Acute  febrile  illness  (axillary  temperature  >37.5 ºC  or  oral  temperature  of  >38.0ºC)  of  more  than  48  hours’  duration  that  does  not  respond  to  antibiotic  or  antimalarial therapy, and is associated with: 

  • Direct contact with sick or dead animal or its products AND/OR 
  • Recent travel (during last week) to, or living in an area where, after heavy rains, livestock die or abort, and where RVF virus activity is suspected/confirmed AND/ OR 
  • Abrupt  onset  of  any  1  or  more  of  the  following:  exhaustion,  backache,  muscle  pains, headache (often severe), discomfort when exposed to light, and nausea/vomiting AND/ OR: 
  • Nausea/vomiting, diarrhoea OR abdominal pain with 1 or more of the following:  
    • Severe pallor (or Hb < 8 gm/dL) 
    • Low platelets (thrombocytopenia) as evidence by presence of small skin and mucous membrane haemorrhages (petechiae) (or platelet count < 100x109/d 
    • Evidence of kidney failure (edema, reduced urine output) (or creatinine > 150mol/L) AND/OR 
    • Evidence of bleeding into skin, bleeding from puncture wounds, from mucous membranes or  nose, from  gastrointestinal  tract  and  unnatural  bleeding  from  vagina AND/OR 
    • Clinical jaundice (3-fold increase above normal of transaminases) 

Late stages of diseases or complications: (2-3 weeks after onset) 

  • Patients who have experienced, in the preceding month a flu-like illness, with clinical criteria, who additionally develop the following: 
    • CNS manifestations which resemble meningo-encephalitis AND/OR: 
    • Unexplained visual loss OR 
    • Unexplained  death  following  sudden  onset  of  acute  flu-like illness  with  haemorrhage,  meningo-ecephalitis,  or  visual  loss  during the preceding month. 

Confirmed case: 

Any  patient  who,  after  clinical  screening,  is  positive  for  anti-RVF  IgM  ELISA  antibodies  (typically  appear  from  fourth  to  sixth  day  after  onset  of  symptoms)  or  tests positive on reverse transcriptase polymerase chain reaction (RT-PCR). 

Transmission to human is mainly through direct or indirect contact with blood or organs of infected  animals. The virus can be transmitted to human through:

  • Handling of animal tissue during slaughtering or butchering, assisting with animal births, conducting veterinary procedures
  • Inoculation  e.g.  via  wound  from  infected  knife  or  through  contact  with  broken  skin  or through inhalation of aerosols produced during the slaughter of an infected animals
  • Infected mosquito

Human become viraemic; capable of infecting mosquitoes shortly before onset of fever and for the  first 3–5 days of illness. Once infected, mosquitoes remain so for life. 

Clinical Diagnostic Criteria 

  • Acute febrile illness that does not respond to antibiotic or antimalarial therapy 
  • Exhaustion, backache, muscle pains, headache (often severe) 
  • Photophobia 
  • Nausea/vomiting 
  • Evidence of bleeding into skin, bleeding from puncture wounds, from mucous membranes or nose, from gastrointestinal tract and unnatural bleeding from vagina 
  • Clinical jaundice (3-fold increase above normal of transaminases) 

Clinical diagnosis is difficult, because RVF symptoms can be mild and non-specific, especially early in the course of the disease.  

Laboratory InvestigationsDefinitive  diagnosis  of  RVF  involves  laboratory  testing  of  blood  (during  illness)  or  other  tissue  samples (postmortem tissue).   

The virus detection in the blood then virus isolation in cell culture  

  • Molecular techniques (reverse transcriptase polymerase chain reaction or RT-PCR)
  • Antibody  testing  using  Enzyme-Linked  ImmunoAssay  (ELISA)  confirms  infection  with RVFV  
  • IgM  antibodies  reflect  a  recent  infection  and  IgG  antibodies  persist  for  several  years (detection of anti-RVF IgM suggests an ongoing transmission of RVFV in humans during  inter-epidemic periods)
  • FBC  
    • Low Hb [Hb<8gm/dL - Severe pallor 
    • Low  platelet  <  100  x109  /Dl (Thrombocytopenia  –  small  skin  and  mucous membrane hemorrhages (Petechiae))   
  • Serum Creatinine  

Note:  Acute RVF can be diagnosed using several different methods 

  1. Serological tests such as ELISA may confirm the presence of specific IgM antibodies to the virus. The virus itself may be detected in blood during the early phase of illness  or  in  post-mortem  tissue  using  a  variety  of  techniques  including antigen  detection  tests by ELISA, RT-PCR, virus propagation (in cell cultures), immunohistochemistry in  formalin-fixed tissues 
  1. ELISA IgG can be used for retrospective diagnostic

Management  

Management of RVF in humans is mainly supportive as there is no definitive treatment for RVF.  Early  detection  and  management  of  the  disease  is  important.  Human  control  of  RVF  is  through  control  of  the  disease  in  animals  through  a  sustained  vaccination  program  and  limiting  human-animal contact. Use of insecticide treated nets and mosquito repellents can also reduce infections in  human. In addition to human suffering and death, RVF has far reaching economic implications to the  livestock  industry.  In  outbreak  settings,  the  disease  manifestation  includes  non-haemorrhagic  febrile  syndromes,  and  laboratory  testing  should  be  considered  among  persons  with  milder  symptoms suggestive of viral illness. 

Prevention 

People living in or visiting areas with RVF shall be protected from the RVF infection with these steps: 

  • Protect people  from  contact  with  blood,  body  fluids,  or  tissues  of  infected  animals (use PPEs like gloves, boots, long sleeves, and a face shield). 
  • Protect people from unsafe animal products. All animal products (including meat, milk, and blood) should be thoroughly cooked before eating or drinking. 
  • Protect people from mosquitoes and other bloodsucking insects. Use insect repellents and bed nets, and wear long sleeved shirts and long pants to cover exposed skin. 

No vaccines are currently available for vaccination in people at risk of RVF infection. 

Public Health Control Measures 

  • Mobilize the community for early detection and care. 
  • Conduct  community  education  about  the  confirmed  case,  how  the  disease  is  transmitted, and how to prevent contact with tissues of infected animals and avoid  mosquito bites. 
  • Provide information about prevention in the home and when to seek care. 
  • Provide supportive treatment to all cases identified 
  • Collaborate  with  the  animal  health  specialists  to  search  and  document  cases among animals as well.