The Zika virus (ZIKV) is transmitted by the Aedes aegypti mosquito, the same mosquito that transmits dengue (which, in Malaysia, affected 120,836 patients last year with 336 deaths).
Dengue and Zika are also transmitted by the Aedes albopictus mosquito.
Although ZIKV infections are usually transmitted by mosquitoes, they have been reported to have been transmitted by sexual intercourse as well. With about 80% of those infected by ZIKV having no symptoms, sexual transmission may potentially account for more infections than previously suspected.
The clinical features of ZIKV infections are milder than dengue and have been address-ed in a previous article (Fit for life, February 14, 2016).
There is a strong association between ZIKV infection and microcephaly, a condition in which the newborn brain is considerably smaller than normal, with all its attendant consequences; other pregnancy complications like spontaneous abortions, intra-uterine foetal death and congenital malformations; and Gullain Barre syndrome – a condition in which the body’s immune system attacks part of the peripheral nerves.
ZIKV in Malaysia
ZIKV was first isolated in South-East Asia from Aedes aegypti in Bentong, Pahang, in 1966 [Source: Marchette et al. Isolation of Zika virus from Aedes aegypti mosquitoes in Malaysia. Am J Trop Med Hyg 1969; 18(3): 411-5].
This meant that human cases almost certainly have occurred in Malaysia, even if never reported. This is supported by reports of ZIKV antibodies in up to 30% of human samples collected in the 1950s and 1990s in Malaysia [Source: Smithburn KC. Neutralizing antibodies against arthropod-borne viruses in the sera of long-time residents of Malaya and Borneo. Am J Hyg 1954; 59(2): 157-63; Wolfe ND et al. Sylvatic transmission of arboviruses among Bornean orangutans. Am J Trop Med Hyg 2001; 64(5-6)].
ZIKV infection was diagnosed in a German tourist who visited Sabah in 2014 [Source: Tappe D et al. Acute Zika virus infection after travel to Malaysian Borneo, September 2014. Emerg Infect Dis 2015; 21(5): 911-3].
These reports indicate that ZIKV is likely to have been present in Malaysia for decades.
The moderate ZIKV antibody rates reported previously may be due to cross-reactivity with other endemic viruses, like dengue. If these rates are reflective of endemic disease, then the population may already have some degree of immunity, unlike in Central and South America, where ZIKV had never been reported previously.
If so, this may help limit outbreaks and its severity in Malaysia.
Will there be ZIKV infections in Malaysia? The most likely answer is yes. It would be a very brave person to say no.
There are several favourable factors for ZIKV infections in Malaysia.
They include almost the whole population living in Aedes-infested areas, the immunity status of whom are not well known; large numbers of travellers from active outbreak areas in South and Central America to North America and Europe; high volumes of air traffic between North America, Europe and Asia, and within Asia; importation of cases during the Aedes breeding season; ZIKV imported into dengue-endemic areas; sexual transmission of ZIKV; difficulty in diagnosis of ZIKV; limited laboratory support; unavailability of a vaccine; and unpublicised surveillance structures.
The growing number of cases in Asia, in particular, Thailand, Indonesia and Singapore, is of concern. Any one of these cases, particularly if undiagnosed, can be a source of imported ZIKV infection because of the high volume of intra-Asean travel.
The current ZIKV outbreak has alarmed most countries, and the World Health Organization (WHO) declared it a public health emergency of international concern on February 1.
Are we prepared?
The WHO developed a Strategic Response Plan in February. It focuses on “preventing and managing medical complications caused by Zika virus infection by targeting pregnant women, their partners, their households and their communities, and expanding health systems’ capacities for that purpose; and integrated mosquito management, sexual and reproductive health counselling, as well as health education and care within the social and legal contexts of each country”.
There are recommended activities for three objectives: public health risk communication and community engagement activities; vector control and personal protection against mosquitoes; and care for those affected and advice for their caregivers.
Surveillance and response indicators to measure a country’s preparedness have been recommended by WHO.
The former include establishment of baseline rates of microcephaly and Gullain Barre syndrome; and laboratory capacity for RT-PCR (reverse transcription polymerase chain reaction) and ELISA (enzyme-linked immunosorbent assay) + PRNT (plaque-reduction neutralisation tests).
The latter includes hospitalisation rates of ZIKV-associated Gullain Barre syndrome; neuroimaging rates in ZIKV-associated microcephaly; ultrasound screening rates in ZIKV-confirmed pregnancies; risk communication strategy and/or implementation plan; routine vector surveillance; resistance to insecticide; and sites that report on the impact of vector control measures.
The WHO has rung the alarm bells. How prepared is Malaysia?
Which of the surveillance and response indicators are in place? What about the indicators that are not in place?
Clinicians have many unanswered questions. Are there registers for microcephaly and Gullain Barre syndrome, and if so, what are the mechanisms for data collection and analysis?
What are the processes to deal with suspected cases? Which healthcare facilities can be utilised for diagnostic and therapeutic purposes?
A particularly relevant question is about the response to the threat from the ubiquitous Aedes mosquito, which transmits dengue, Japanese encephalitis, chikungunya, ZIKV and yellow fever, and how effective it is?
Are there local practice guidelines from the Health Ministry, and if so, how can clinicians access them? If not, which guidelines are recommended?
That there is a need for an adequate and transparent pre-emptive response from policy makers, as soon as possible, to avert a likely outbreak of ZIKV infection, with potential catastrophes for those infected, is not an understatement.
Dr Milton Lum is a past president of the Federation of Private Medical Practitioners Associations, Malaysia and the Malaysian Medical Association. The views expressed do not represent that of organisations that the writer is associated with. The information provided is for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.