9.1 Arboviruses

Status

CHAGAS DISEASE

Overview

Chagas Disease is a parasitic disease resulting from infection with Trypanosoma spp. (e.g. Tyrpanosoma cruzi). The Trypanosoma parasites are transmitted through the bite of an infected triatomine bug also known as a “kissing bug”. About 6 to 7 million persons worldwide are estimated to be infected with Chagas disease although most cases occur in Latin America. The region of the Americas is also at risk. Additional routes of transmission include food-borne, blood transfusions or congenital (mother-to-child).

Surveillance Procedures:

Step 1: Case Detection and Reporting –

Healthcare Providers / Laboratory Personnel

Immediately report all suspected cases. Reports should be shared with laboratory personnel for confirmation.

Clinical presentation

There are two phases of the infection: acute and chronic. In most cases the acute phase presents with symptoms that are mild, unspecific, or asymptomatic.  However, in some cases, this can progress to a skin lesion or swelling of the lids of one eye with additional symptoms of fever, headache, muscle pain and chest pain with difficulty in breathing.

During the chronic phase, also known as the “chronic indeterminate,” the parasites would have mostly cleared the blood circulation and entered the heart and digestive system. This causes a range of digestive and cardiac disorders in some patients. It is theorized that infection of the heart muscles with Trypanosoma parasites can lead to progressive heart failure. 

Step 2. Laboratory Confirmation

Samples are taken to the labs to be tested (collection and transport details below)

Laboratory Criteria for Diagnosis (Ref: ADHS Communicable Disease Case Definitions 2020)

Confirmatory Testing

• Isolation of T. cruzi by microscopy (microscopic examination, wet mount, thick and thin smears Giemsa stain), OR
• Isolation of T. cruzi by culture, OR
• Detection of T. cruzi DNA by polymerase chain reaction (PCR), OR
• Detection of antibody specific to T. cruzi by two distinct diagnostic assays (can only be performed at CDC)

Presumptive Testing

• Evidence of T. cruzi antibodies on a single serologic diagnostic assay (IgG positive; not blood screening); OR
• Reactive blood donor screen AND a secondary positive diagnostic assay (IgG positive). (Note that ‘additional’ or ‘confirmatory’ antibody tests performed by a blood screening agency do not count as diagnostic tests. See Comments.)

Case Classification

Confirmed - A case that meets the confirmatory laboratory criteria.

Probable - A case that meets the presumptive laboratory criteria.

Type Classification

Acute phase - Asymptomatic or symptomatic within 8 weeks of documented exposure or symptom onset/diagnosis

Chronic, intermediate phase- Asymptomatic case > 9 months of age and > 8 weeks since documented exposure

Chronic, symptomatic phase- Symptomatic case > 9 months of age and > 8 weeks since documented exposure

Step 3. Reporting

Reports of all confirmed cases should be shared with the Epidemiology Unit

Step 4: Data Management (Epi Unit)

• Data should be cleaned and analysed
• Preparation of a report should be done on the evolution of the epidemiological situation of the disease
• Dissemination of a weekly situation report

If an outbreak occurs:

Control

Control of Chagas disease is through control of the vector. Entomological investigations around the localities (residences) of infected individuals are recommended for detection and identification of the vector. Further to confirmation of the vector, the appropriate vector control measures should be used. 

Once the vector is confirmed to be present in a region, health education should focus on personal protective measures to prevent infestation e.g. use of bed nets and insect-proofing of windows and doors.

CHIKUNGUNYA FEVER (CHIK)

Overview

Chikungunya fever (CHIK) is an emerging, mosquito-borne disease caused by an alphavirus; Chikungunya virus (CHIKV). The disease was first identified during an epidemic of fever, rash and arthritis in Tanzania in 1952 – 1953. Subsequently there have been sporadic outbreaks in regions of Africa, Asia and Europe (Italy). In December 2013, confirmation of the first cases of autochthonous transmission of chikungunya in the Americas (Caribbean) was made.

Chikungunya is transmitted predominantly by the bites of infected Aedes aegypti and Ae. albopictus mosquitoes, the same species involved in the transmission of dengue. The onset of illness usually occurs between 3 and 7 days after infection but the incubation period can range from 2 to 12 days.

Clinical presentation

The disease is characterized by an abrupt onset of fever and joint pain. Other symptoms include muscle pain, headache, nausea, and rash. Following acute infection, chronic joint pains may persist for months or years along with fatigue and depression. 

There is no specific treatment or vaccine available for Chikungunya. Most patients recover fully. Serious complications are not common, but older people, children and pregnant women may be more severely affected by the disease. 

Surveillance Procedures:

Step 1: Case Detection and Reporting – Healthcare Providers / Laboratory Personnel

Report all suspected cases within 24 hours. Reports should be shared with laboratory personnel for confirmation.

Case Definition

Suspect case: a patient with acute onset of fever >38.5ºC (101.3ºF) and severe arthralgia or arthritis not explained by other medical conditions, and who resides or has visited epidemic or endemic areas within two weeks prior to the onset of symptoms.

Confirmed case: a suspect case with any of the following CHIK specific tests:

• Viral isolation. Detection of viral RNA by RT-PCR.
• Detection of IgM in a single serum sample (collected during acute or convalescent phase).
• Four-fold increase in CHIKV-specific antibody titres (samples collected at least two to three weeks apart)(5)
• Viral isolation.

Step 2. Laboratory Confirmation

Samples should be taken to the labs to be tested (collection and transport details below)

Laboratory diagnosis

Laboratory Confirmation

Three main types of laboratory tests are used for diagnosing CHIKV: 

• Reverse transcriptase-polymerase chain reaction (RT-PCR) for the detection of CHIKV RNA from serum obtained from whole blood.
• Serology (immunoglobulin M [IgM] and G [IgG] ELISA) and plaque reduction neutralization testing (PRNT) in serum obtained from whole blood. The serum (or blood) specimen should be transported at 2°−8°C and should not be frozen. Serologic diagnosis can be made by demonstration of IgM antibodies specific for CHIKV or by a four-fold rise in PRNT titre in acute and convalescent specimens.
• Virus isolation from acute serum specimens (≤5 days). 

Table 10. Typical results of samples tested at various time points post-infection.

Collection, Storage, and Transportation of Samples

Collection of samples for serology, isolation and molecular diagnosis:

Sample: Serum

Time of collection: Acute, within the first eight days of illness; convalescent, 10−14 days after acute specimen collection.

To collect serum:

• Aseptically collect 4−5 ml of venous blood in a tube or a vial.
• Allow blood to clot at room temperature, centrifuge at 2,000 rpm to separate serum. Collect the serum in a clean dry vial.
• All clinical samples should be accompanied by their clinical and epidemiological information.

Other types of specimens for laboratory investigation:

Specimens:

• CSF in meningoencephalitis cases.
• Synovial fluid in arthritis with effusion.
• Autopsy material – serum or available tissues.

[Note: Mosquitoes collected in the field will also be handled using the same techniques described here]

Transportation of Samples:

• Transport specimens to the laboratory at 2°−8°C (icebox) as soon as possible.
• Do not freeze whole blood, as haemolysis may interfere with serology test results.
• If a delay greater than 24 hours is expected before specimens can be submitted to the laboratory, the serum should be separated and stored at refrigerated temperature.
• Serum samples for virus isolation and molecular diagnosis should be stored frozen (at −20°C for short-term storage or at −70°C for long-term storage) (6).

Step 3. Reporting

Reports of all confirmed cases should be shared with the Epidemiology Unit

Step 4: Data Management (Epi Unit)

• Data should be cleaned and analysed
• Preparation of a report should be done on the evolution of the epidemiological situation of the disease
• Dissemination of a weekly situation report

Notes:

Patient Isolation Recommendations

To prevent the infection of others in the household, the community, or the hospital, a patient with acute CHIKV should avoid being bitten by Ae. aegypti or Ae. albopictus mosquitoes during the viraemic phase, which is usually the first week of illness. 

DENGUE FEVER

Overview

Dengue is an acute febrile illness caused by one of the four types of dengue virus (DEN-1, DEN-2, DEN-3 and DEN-4). The four serotypes circulate in the Caribbean region; however, DEN-1 and DEN-2 predominate. Viral transmission is through the bite of an infective Aedes aegypti mosquito. The disease occurs in all countries infested with the vector and is prevalent in the Caribbean. Dengue is usually seasonal, with an increase in cases occurring after the onset of the rainy season.

The incubation period of dengue is usually 4 to 10 days with a range of 3 to 15 days. Patients are infectious for mosquitoes during the period of viraemia which lasts for 5 days from the day before onset of fever. 

Clinical presentation

The illness is characterized by an abrupt onset of fever accompanied by headache, myalgia, arthralgia, retro-orbital pain and rash. In its early stages it may resemble influenza, rubella or measles.

Antibody to the dengue viruses is protective and long lasting but is type specific so that an individual can be infected with each of the 4 types. Reinfection of an individual with a different type may result in the severe forms of the disease.

The objective of surveillance for dengue fever is to anticipate large outbreaks of disease in order to reduce virus circulation through vector control and to avoid the high morbidity associated with epidemics. A second objective is to track the circulation of the four serotypes, particularly the introduction of a new serotype into a country and the consequent risk of Severe Dengue.

Surveillance Procedures:

Step 1: Case Detection and Reporting – Healthcare Providers / Laboratory Personnel

Report all suspected cases within 48 hours. Reports should be shared with laboratory personnel for confirmation.

Case Classification

Suspected dengue case

Dengue without warning signs (DNWS):

A person who lives in a dengue endemic region or has travelled to areas with dengue transmission in the last 14 days and presents with fever, usually of 2 to 7 days duration, and two (2) or more of the following features:

• Nausea/ vomiting
• Exanthema (rash)
• Headache/ retro-orbital pain
• Myalgia and arthralgia
• Petechiae or positive tourniquet test
• Leukopenia

A case also includes any child coming from or living in an area with dengue transmission, with acute febrile illness, usually of 2 to 7 days and no apparent cause.

Dengue with warning signs (DWWS):

A dengue case that, near or preferably at defervescence, presents one or more of the following signs:

• Intense abdominal pain or tenderness
• Persistent vomiting
• Fluid accumulation (ascites, pleural effusion, pericardial effusion)
• Mucosal bleed
• Lethargy/restlessness
• Postural hypotension (lipothymia)
• Liver enlargement >2 cm
• Progressive increase in hematocrit

Severe Dengue (SD)

A dengue case that has one or more of the following manifestations:

• Shock or respiratory distress due to severe plasma leakage.
• Shock evidenced by tachycardia, weak or undetectable pulse, cold extremities, and capillary refill time >2 seconds, pulse pressure ≤ 20 mmHg: hypotension in late phase.
• Severe bleeding: based on evaluation by the attending physician (e.g. hematemesis, melena, ample metrorrhagia, central nervous system bleeding).
• Severe organ involvement, such as liver impairment (AST or ALT ≥1000 IU), central nervous system (impaired mental state), heart (myocarditis), or other organs (7).

Note:

All severe cases of dengue should be confirmed by laboratory tests specific for dengue.  Dengue with warning signs and Severe Dengue require strict observation and medical intervention.

Probable dengue case

Any suspected dengue case that has a positive IgM or non-structural protein (NS1) result, or clinical-epidemiological link.

Note: During outbreaks, reported cases that could not be investigated are also considered probable dengue cases, since it is considered that all have a clinical-epidemiological link.

Confirmed dengue case

Any dengue case that is laboratory-confirmed (by molecular techniques, such as conventional RT-PCR, real-time RT-PCR, or others; IgM or IgG seroconversion in paired sera or a fourfold IgG titre increase; viral isolation).

Note: During an epidemic it is unnecessary to continue laboratory investigation of all suspected cases after the diagnosis of dengue has been established and the virus type identified. The great majority of cases will be epidemiologically linked.

Laboratory surveillance should be restricted to the collection of specimens from a limited number of probable cases in order to:

• Identify the introduction of any new serotypes into already infected areas
• Identify spread of the epidemic into new areas
• Monitor severe, complicated and fatal cases attributed to dengue fever

Death from dengue

Every patient who meets the definition for suspected, probable, or confirmed case who dies as a consequence of dengue.

Ruled out case

Any suspected case of dengue that meets one or more of the following criteria:

• Negative laboratory diagnosis. (Ensure that samples were obtained within the adequate time frame)
• No clinical-epidemiological link
• Has laboratory diagnosis of another clinical disorder
• A case without laboratory testing whose clinical and epidemiological investigations are compatible with suspicion of other disorders 

Laboratory confirmation of any dengue type not previously identified in a country or not detected in the country for several years should be immediately reported.

Step 2. Laboratory Confirmation

Samples should be taken to the labs to be tested (collection and transport details below)

Laboratory diagnosis

Specimen Collection and Transport

Acute blood sample

It is preferable to collect this within 3 days of onset to increase the probability of virus identification. However, if the patient presents at a later date a sample should still be collected and forwarded to the laboratory.

• Draw a 5 to 10ml blood sample from each suspected case and place in a sterile tube.
• Send to the laboratory immediately in a cold box at 4–8°C.
• If shipment is to be made outside of the country and shipment is not possible within 48 hours, centrifuge the blood and transfer the serum to a sterile vial.
• Store at –20°C and ship with frozen icepacks (This sample will be used for serology only).
• Label all tubes and vials with patient name, specimen and date of collection.
• Complete a laboratory request form including date of onset of illness, symptoms and date of specimen collection.

Convalescent blood sample

Only if requested by the laboratory, draw a 5ml convalescent blood sample 2 to 3 weeks after the first. Store and ship as above.

Laboratory Confirmation

A laboratory confirmed case of dengue is a probable case with one or more of the following:

• Detection of IgM antibodies to one or more of the dengue virus antigens by capture ELISA (this test is most reliable on blood taken more than 5 days after onset).
• Isolation and identification of dengue virus from acute serum (collected within 3 days of onset) and shipped immediately to the laboratory at 4–8°C.
• Demonstration of dengue virus antigen in autopsy tissue, serum or cerebrospinal fluid samples by immunohistochemistry, immunofluorescence or ELISA
• Demonstration of dengue virus genomic sequences in autopsy tissue, serum or cerebrospinal fluid samples by polymerase chain reaction (PCR).
• Demonstration of a fourfold or greater rise in flavivirus antibody (IgM/IgG) titres between acute and convalescent phase serum specimens (7).

Step 3. Reporting

Reports of all confirmed cases should be shared with the Epidemiology Unit

Step 4: Data Management (Epi Unit)

• Data should be cleaned and analysed
• Preparation of a report should be done on the evolution of the epidemiological situation of the disease
• Dissemination of a weekly situation report

MALARIA

Overview

Malaria is a parasitic disease resulting from infection with the Plasmodium spp. (P. falciparum, P. vivax, P. ovale, and P. malariae). The Plasmodium spp. parasites are transmitted through the bite of the infected female Anopheles mosquito. About half of the world’s population are at risk of being infected with malaria although most cases occur in sub-Saharan Africa. The region of the Americas is also at risk. Children under 5 years are the most vulnerable group affected and account for a large percentage of deaths annually.

Clinical presentation

Most cases will experience fever and rigors which is usually cyclical in occurrence (malaria paroxysms). The cycle of abrupt chills, fever (39 – 41o C) and sweating is repeated either daily, every other day, or every third day depending on the infecting species of Plasmodium. Other commonly associated symptoms include malaise, headache, myalgia, nausea and vomiting. Splenomegaly and hepatomegaly also occur.

Plasmodium falciparum generally causes the most severe disease with cerebral-related findings (confusion, coma, neurologic signs and convulsions), respiratory difficulties (pulmonary oedema), haemolytic anaemia, dark urine, anuria and diarrhoea. 

Surveillance Procedures:

Step 1: Case Detection and Reporting – Healthcare Providers / Laboratory Personnel

Report all suspected cases immediately. Reports should be shared with laboratory personnel for confirmation.

Case Definition

1. Suspected case - A person with chills followed by fever and sweating and/or rapid diagnostic test (RDT) detection of plasmodium species.
2. Confirmed case - A suspected case with laboratory confirmation – identification of Plasmodium species on peripheral blood smear or using PCR.

Confirmed cases are classified as follows:

• Imported: Malaria acquired outside the country.
• Autochthonous Indigenous: Malaria acquired by mosquito transmission in an area where malaria is a regular occurrence.
• Introduced: Malaria acquired by mosquito transmission from an imported case in an area where malaria is not a regular occurrence
• Induced: Malaria acquired through artificial means (e.g. blood transfusion, sharing of syringes or needles)
• Congenital: Malaria acquired through transplacental transmission
• Cryptic: An isolated case of malaria not associated with secondary cases, as determined by appropriate epidemiologic investigations.
• Relapsing: Recurrence of disease after it has been apparently cured. Relapses are caused by reactivation of dormant liver-stage parasites (hypnozoites) of P. vivax and P. ovale. (CDC, 2014)

Step 2. Laboratory Confirmation

Samples should be taken to the labs to be tested (collection and transport details below)

Laboratory diagnosis

Laboratory confirmation

• The detection of specific antigens (proteins) produced by malaria parasites in the blood of infected individuals using malaria rapid diagnostic tests (RDTs).
• The identification of the Plasmodium parasite in thick or thin peripheral blood film. The species of Plasmodium should also be reported — P. vivax, P. malariae, P. ovale, P. falciparum or mixed.
• Detection of DNA of specific species of plasmodium in a sample of peripheral blood using Polymerase Chain Reaction (PCR).
• Immunofluorescent Antibody Test (IFAT) – a blood drop from a finger prick is collected on a strip of special filter paper and examined for antibody. This serological test is a useful tool when a large number of persons are being screened.

Specimen Collection and Transport

Thick and thin blood smears

These are taken from the peripheral blood stream and remain the mainstay of diagnosis. Because the level of parasitaemia varies from hour to hour, especially for P. falciparum infections in which parasite may be difficult to find, blood should be examined at 8-hour intervals ideally, for 3 days, during and between febrile spikes. Infection is more readily detected on a thick film and the less sensitive thin film is used primarily for species identification.

Ensure that slides with the blood films are properly labelled. Dates are important since serial specimens are taken from each case and the results are important to case management.

Blood for serology

Serologic tests are not used in diagnosis of acute attacks since they do not distinguish between antibody from present and past infections which may persist for 10 years or more.

However, the Immunofluorescent Antibody Test (IFAT) provides a useful tool for screening in epidemics or where large numbers of cases are involved, so that the taking of blood smears may be prioritized.

Notes:

Control and Prevention of Malaria

• Prompt investigation of suspected cases and close surveillance of those at high risk.
• Immediate commencement of treatment of confirmed cases (results of sequential blood smears should give an indication of drug resistance and the need for modification of chemotherapeutic regime). Artemisinin-based combination therapy such as artemether/lumefantrine is usually the drug of choice.
• Nurse patient in mosquito-proof area, especially from dusk to dawn.
• Investigate contacts and try to identify the source of infection. The latter may provide a lead to other cases with inapparent infection.
• Undertake “Active Fever Surveillance” – examine smears from febrile persons presenting to health facilities in case vicinity.
• Undertake “Active Geographical Surveillance” – examine smears from persons living in surrounding households – with or without fever. A one-mile radius around a positive household is a commonly used guide.
• In epidemics, plot epidemic curve utilizing line listing data, and use spot maps to monitor distribution of cases and direct vector control activity.
• Maintain updated information on endemic countries and those in which epidemics are occurring as an item of surveillance data.
• Put in place systems to facilitate access to information on countries visited by travellers, e.g., collaboration with Immigration Department, links with travel agencies, regular tour organizers and airlines may provide information useful for traveller surveillance.
• Provide appropriate chemoprophylaxis for persons travelling to endemic areas.
• Maintain the use of Health Alert Cards for arriving passengers at Ports of arrival.
• In endemic areas, examine blood for parasites as part of routine screening at blood banks.
• Educate the public on the mode of transmission and of precautions which can help to prevent contracting malaria.
• Institute measures to reduce the Anopheles population in endemic areas, in areas surrounding locations where cases have been identified, and around the premises where the patient has been 30 days prior to the onset of illness (aim at covering a radius of 1 mile around these areas).
• Maintain rigid anti-mosquito control for 400 meters around the perimeter of airports and seaports.

Step 3. Reporting

Reports of all confirmed cases should be shared with the Epidemiology Unit

Step 4: Data Management (Epi Unit)

• Data should be cleaned and analysed
• Preparation of a report should be done on the evolution of the epidemiological situation of the disease
• Dissemination of a weekly situation report

Technical Notes

The first attack in a country regardless of whether the person has had previous attacks in other countries should be counted as a new case in that country. A subsequent attack in the same person in the same country caused by a different Plasmodium species should be counted as another case.

A subsequent attack in the same person in the same country caused by the same Plasmodium spp. may indicate relapsing infection, or treatment failure due to drug resistance.

In areas where other diseases with similar symptomatology are prevalent, especially other diseases spread by vectors (e.g. yellow fever and dengue), co-infection should be considered even with the demonstration of malarial parasites. 

Syndromic Surveillance of Select Vector Borne Diseases

Chikungunya, dengue, Zika, Yellow fever and Malaria will be reported under undifferentiated fever. Dengue and Yellow fever may also present with bleeding and be reported as fever and haemorrhagic syndrome.

Environmental Health

The mosquito vectors (Aedes) that transmits these diseases breeds in domestic and peri-domestic such as in water storage containers, flower vases, vehicle tyres, coconut shells and other discarded items. Public health authorities should:

• Conduct surveillance of Aedes mosquito species to determine density and distribution of the population and to identify the communities at risk for disease transmission.
• Monitor the seasonality of the trends in vector borne diseases so that interventions can be intensified in anticipation of the usual increases in incidence.
• Conduct larval survey measurements such as the house index, container index and Breteau index to monitor the mosquito population in different areas.
• Conduct sampling of adult mosquito to obtain information on disease transmission risk and the effectiveness of control interventions.

Traveller’s Health

Visitors to the Caribbean from non-endemic regions may become infected while on vacation and fall ill on return to their homelands. This can lead to negative publicity, travel advisories, a reduction in visitor arrivals and economic loss to the sector. 

Public health authorities should:

• Monitor areas with high levels of vectors and target them for control interventions.
• Maintain control of mosquito vectors around tourist accommodations to limit the impact of arboviral diseases on this sector.
• Educate travellers of the need to use personal prevention measures.

Control and Prevention of Mosquito Borne Diseases

Prevention is reliant on upon the measures taken to avoid mosquito bites and on the elimination of mosquito breeding sites. It is important to strengthen disease surveillance systems to detect and respond to outbreaks of vector borne diseases.

To avoid mosquito bites individuals are advised to:

• Wear long-sleeved shirts and long trousers; especially at dawn and dusk when Aedes mosquitoes are most active.
• Use mosquito repellents on parts of the body that are exposed.
• Use repellents such as mosquito coils, electric vapour mats during the daytime to prevent mosquito bites.
• Use mosquito bed nets to protect individuals who may sleep during the day (insecticide treated nets are effective at preventing mosquito bites during sleep). Nurse febrile patients in screened rooms or use insecticide-impregnated bed nets.
• Use screens on windows and doors to keep mosquitoes out of dwellings.

Vector control measures include

• Use of chemical insecticides in the recommended dose to kill adult mosquitoes (through fogging or ultra-low volume (ULV) application of insecticide especially in a one-mile radius surrounding confirmed cases).
• Elimination of breathing sites of mosquitoes by removing containers that can hold water such as flower vases, tyres, cans, jars, coconut shells, etc.
• Treating water containers with larvicide to destroy the larval stage of Aedes mosquitoes and prevent the emergence of adult mosquitoes.

Integrated vector management (IVM)

Integrated vector management is a framework for managing vector populations in such a way as to reduce or interrupt transmission of disease. Components of IVM include:

• A strengthened public health regulatory and legislative framework that facilitates the inclusion of vector control in the policies of all relevant agencies, organizations and among civil society.
• Evidence-based decision making – the methods employed are based on knowledge of factors influencing local vector ecology, epidemiology, surveillance and resources.
• biology, disease transmission and morbidity;
• Use of a range of interventions, often in combination and synergistically;
• Collaboration within the health sector and with other public and private sectors that impact on vectors;
• Engagement with and empowerment of local communities and other stakeholders to facilitate the adoption of measures that limits the proliferation of vectors and the transmission of diseases.(6)

YELLOW FEVER

Overview

Yellow Fever is an acute viral haemorrhagic fever transmitted to man by mosquitoes infected with the yellow fever virus. It is endemic in parts of Africa, South America and occasionally enzootic in Trinidad.

The virus exists in three transmission cycles: (1) Jungle yellow fever transmitted between monkeys and forest-dwelling mosquito species such as Haemagogus sp. in South America and Aedes africanus in Africa., (2) Intermediate transmission occurs in semiarid regions of Africa where mosquitoes feed both on primates (monkeys) and humans, given the opportunity, and (3) Urban yellow fever transmitted between man and the Aedes aegypti mosquito. Susceptible humans can become infected if they enter the forest when the virus is active and are bitten by infected forest mosquitoes.

Clinical presentation

The incubation period of yellow fever is 3 to 7 days and the illness is characterized by an acute phase lasting 4 to 5 days with fever, chills, headache, dizziness, malaise, nausea and lower back pain. Relative bradycardia, conjunctival injection, and facial flushing may be found on physical examination. A short period of remission lasting about 24 hours follows. About 15 – 25% of cases experience a toxic phase of 3 to 5 days duration with a very high fatality rate. The toxic phase is marked by fever, abdominal pain, vomiting, renal failure, and haemorrhagic manifestations such as petechiae, ecchymoses, epistaxis, bleeding from gums and venepuncture sites, melena, hematemesis, and metrorrhagia. Jaundice and elevated liver enzymes (AST > ALT) are also prominent (Blyth, 2019).

Confirmation of yellow fever rests on laboratory diagnosis since the disease, in its wide range of clinical severity, can resemble many others. The differential diagnoses include influenza, dengue fever, malaria, hepatitis, leptospirosis and other viral haemorrhagic fevers.

Surveillance for yellow fever permits rapid identification and laboratory confirmation of cases leading to prompt outbreak control through immunization and vector reduction.

Case Definition

Suspected case

A suspected case of yellow fever is a person with an illness characterized by:

• Acute onset of fever followed by two or more of the following symptoms:
  • Headaches or backaches
  • Muscle pain
  • Nausea and/or vomiting
  • Fatigue/lethargy 

AND at least one of the following:

• Jaundice (within two weeks of the onset of fever)
• Reduced amounts of urine production
• Bleeding from nose, gums or skin
• Blood in vomit, stool or urine

Probable case

A probable case of yellow fever is a suspected case fulfilling one or more of the following criteria:

• Living/working in an area where yellow fever is enzootic or endemic
• Presence in the neighbourhood or village, within the last two weeks, of a person ill with fever and jaundice

Confirmed case

A confirmed case of yellow fever is a suspected case with positive laboratory test results or is epidemiologically linked to a laboratory confirmed case.

Laboratory diagnosis

Specimen Collection and Transport

Acute blood sample

• Draw a 5 to 10ml blood sample from each suspected case and place in a sterile tube.
• Send to the laboratory immediately in a cold box.
• If shipment is not possible within 24 hours, centrifuge the blood and transfer the serum to a sterile vial.
• Store at –20°C and ship with frozen icepacks.
• Label all tubes and vials with patient name, specimen and date of collection.

Convalescent blood sample

• If requested by the laboratory draw a 5ml convalescent blood sample 2 to 3 weeks after the first.
• Store and ship as above.

Autopsy specimens

• Blood: Place a 10ml sample of heart blood into a sterile vial, label and ship to the laboratory within 24 hours.  If prompt shipment is not possible store and ship as in (a) above.
• Liver: Place a section of liver, at least one cm3, into a sterile jar with viral transport medium or buffered saline. Store and ship at 4°C

OR

Place liver specimen in normal saline and ship at ambient temperature.

All specimens must be accompanied by patient identification, clinical data and recent yellow fever immunization history.

Laboratory confirmation

Criteria for case confirmation.

A case is laboratory confirmed as yellow fever if one of the following criteria are met.

• Yellow fever-specific IgM antibodies are detected in the serum and there is no history of recent immunization.
• Yellow fever virus is isolated from blood or liver by culture.
• Paired sera show a four-fold or greater increase in yellow fever specific antibody level in the absence of recent vaccination.
• Yellow fever viral antigen or genome is detected in blood or tissue by RT-PCR.
• Characteristic liver histopathology is seen at autopsy.

Other laboratory examinations

Laboratory tests for some of the other possible aetiologic agents should be conducted if the capability exists. These might include Malaria blood film, Hepatitis A and B serology, Dengue IgM or virus isolation, Leptospirosis agglutination test, and immunofluorescence for selected viral haemorrhagic fevers.

Yellow Fever Control and Prevention

Outbreak control

Upon confirmation of a case of yellow fever, action can be initiated at the district level which will reduce the severity of, or even abort, the threatened epidemic.

Appropriate measures are:

• Conduct emergency immunization in the district.  (More extensive immunization must be planned at the national level.)
• Intensify surveillance to identify additional cases
• Alert nearby districts or counties to the possibility of yellow fever virus circulation
• Coordinate with vector control authorities to reduce Aedes density within a six-mile radius of the case and around hospitals.
• Inform and involve the community in elimination of mosquito breeding sites
• Set up a mapping system for suspected and confirmed cases
• Strengthen clinical management of yellow fever in health facilities

Outbreak prevention

Having brought the outbreak under control attention can be focused on long-term activities which will prevent the recurrence of epidemic yellow fever.

The following are appropriate activities: 

• Conduct a thorough epidemiological analysis of the recent outbreak
• Immunize populations identified by this analysis to be at risk e.g. newly developed peri-sylvatic communities whose residents may not have been immunized, or urban communities potentially exposed.
• Improve yellow fever vaccine coverage in the EPI. This is a long-term strategy to ensure protection of each birth cohort
• Reinforce routine surveillance. Identify areas of weakness in awareness, training, designation of responsibility
• Collaborate with vector control to set up a mosquito monitoring and control programme
• Strengthen the early warning system for epizootic yellow fever.

Technical Notes

Serologic cross-reactions occur with other flaviviruses (i.e. dengue), in the HI test.

Yellow fever vaccine must be approved by WHO and administered by approved persons. An international certificate of vaccination should be filled out, dated, signed and validated. Vaccination is valid for life.

ZIKA

Overview

Zika virus (ZIKV) is an RNA virus that gets its name from the forest in Uganda where it was discovered in 1947. It is an arbovirus of the genus Flavivirus (family Flaviviridae) that is closely related to other viruses such as dengue, yellow fever, West Nile and Japanese encephalitis viruses. It is mainly transmitted by mosquitoes of the genus Aedes, but sexual and vertical (mother-to-child) transmission have been reported. Additionally, a limited number of cases of transmission via blood transfusion have been documented.

Clinical presentation

The incubation period is about 3 to 12 days. Most (1 in 5) cases are asymptomatic. Symptoms of zika infection include rash, fever, conjunctivitis, myalgia, arthralgia, malaise and headache and may last from 4 to 7 days. 

An increase in prevalence of neurological complications, most notably Guillain-Barre Syndrome (GBS) has been observed to coincide with an outbreak of zika infection. Also, birth defects such as microcephaly, placental insufficiency, intrauterine growth retardation and foetal demise have been linked to zika infection in pregnancy. 

Surveillance objectives (PAHO, 2016)

• Enable early detection of imported cases in areas/territories where the mosquito vector is absent;
• Permit early detection of the introduction or presence of clusters of ZIKV infection in an area/territory where the mosquito vector is present, but vector borne transmission has not been previously documented;
• Characterize the epidemiological situation and follow up the outbreak on the basis of the detection of local transmission and monitor the circulation of the virus, taking into account other endemic arboviral diseases;
• Detect unusual events, for example, atypical clinical descriptions of ZIKV infection or a new mode of transmission;
• Detect the occurrence and temporal evolution of neurological manifestations;
• Determine the prevalence of congenital abnormalities at birth, especially those affecting the central nervous system (CNS), such as microcephaly; investigate the birth defects affecting CNS and the potential relation with prior ZIKV infection of the mother;
• Contribute to the knowledge of the disease, its complications, and its sequelae, so as to support the implementation of primary, secondary, and tertiary prevention measures, since it is an emerging disease and its natural history and disease burden are still only partially understood (8).

Case Definitions (PAHO, 2016)

Suspected case of Zika virus disease:

A patient with rash (usually maculopapular and pruritic) with at least two or more of the following signs or symptoms:

• fever, usually < 38.5 °C
• conjunctivitis (non-purulent/hyperaemic)
• arthralgia
• myalgia
• peri-articular oedema

Probable case of Zika virus disease:

A patient who meets the criteria of a suspected case AND also has anti-ZIKV IgM antibodies, without laboratory results indicating infection by other flaviviruses.

Confirmed case of Zika virus disease:

A patient who meets the criteria for a suspected case AND has laboratory confirmation of recent ZIKV infection, with presence of:

• RNA or ZIKV antigen in any serum sample or other type (for example, urine, saliva, tissue or whole blood) by RT-PCR; OR
• Positive anti-ZIKV IgM antibodies AND Plaque reduction neutralization plate (PRNT90) for ZIKV titres ≥ 20 and four or more times higher than for other flaviviruses; and exclusion of other flavivirus; OR
• In deceased individuals, molecular detection of the viral genome in autopsy tissue (fresh or in paraffin), or specific viral antigen detection by immuno-histochemistry testing.

Sample selection and storage

• Samples that will be processed (or sent to a reference laboratory) within 48 hours should be kept refrigerated at 4 °C to 8 °C.
• Samples that will be tested after the first 48 hours but no later than 7 days should be kept frozen at -10 °C to -20 °C.
• Samples that will be processed after a week should be kept frozen at -20 °C to -70 °C. Such samples will keep for prolonged periods.